ElShamah - Reason & Science: Defending ID and the Christian Worldview
Would you like to react to this message? Create an account in a few clicks or log in to continue.
ElShamah - Reason & Science: Defending ID and the Christian Worldview

Otangelo Grasso: This is my library, where I collect information and present arguments developed by myself that lead, in my view, to the Christian faith, creationism, and Intelligent Design as the best explanation for the origin of the physical world.

You are not connected. Please login or register

The cell membrane , and origin of life scenarios

Go down  Message [Page 1 of 1]



The cell membrane , and origin of life scenarios 1


Ricard V. Sole Synthetic protocell biology: from reproduction to computation February 16, 2015

Cellular life cannot be described in terms of only DNA (or any other information-carrying molecule) nor as metabolism or as compartment (cell membrane) alone. Cellular life emerges from the coupling among these three components. A container is a prerequisite of biological organization in order to at least confine reactions in a limited space, where interactions are more likely to occur (Deamer et al. 2002). It also provides a spatial location able to effectively facilitate division of labour among reactions. Moreover, in modern cells, the membrane is an active cell component, channelling nutrients in and waste products out of the cell by means of specialized transport catalysts (Pohorille et al. 2005). A metabolism (Smith & Morowitz 2004) provides the source of non-equilibrium and a means of energy storage required in order to build and maintain cellular components. It is also required to allow cell growth to occur and eventually force splitting into two different (but similar) copies. 6

The production of biological membranes under early earth conditions is no trivial task. 2 The lipid bilayer is a simple structure and at first glance may seem as though it is of little consequence, but life could not have arisen without it. 5 Cells all have a membrane constructed from a phospholipid bilayer. From the very beginning, cells used the lipid bilayer to regulate their internal environment. The bilayer blocked or impeded, the passive flow of most molecules into the cell, thus protecting the cell from the external environment. Cells exploited this property by embedding proteins in their membranes that would allow only certain molecules to gain entry. In this way, the cell could fine-tune the selection of what got in and what did not. Other proteins embedded in the membrane acted like sensory antennae, making it possible for cells to gain information about their immediate environment. Some of these proteins were used to detect the presence of food molecules, while others became specialized as transmitters and receivers, allowing the cells to communicate with each other.

Lipids are fundamental to biology as the compounds from which biological membranes are largely constructed. 4 These can broadly be grouped into two classes, which are found in various types of organisms:

the isoprenoid ether lipids and the
fatty acid acyl lipids

The cell membrane , and origin of life scenarios UQV3gVs

The fatty acid ester type (Figure 5.7b) is widely distributed across the eubacterial and eukaryotic domains of life and consists of the union of one or more straight saturated or unsaturated fatty acid chains. These chains typically contain 16–18 carbon atoms and are derived from the malonyl/acetyl-CoA biosynthetic pathways, joined to a polar head group, which is usually some derivative of glycerol, rendered more polar by the attachment of phosphate, choline, or some other low-molecular-weight moiety (represented as R in Figure 5.7a and b). The isoprenoid ether type (Figure 5.7a) is widely distributed among the archaebacteria (Matsumi et al. 2011), particularly in extremophilic species, perhaps rationalizable by their greater resistance to chemical degradation at extremes of salinity, pH, and temperature (Driessen and Albers 2007). These consist of one or more polyisoprenoid chains (derived from the isoprene biosynthetic pathways), attached by ether linkages to polar head groups such as substituted glycerol moieties.

Prebiotic syntheses of the straight-chain fatty acids have been suggested based on Fischer–Tropsch-type synthesis (FTT), for example, by the reactions of CO or CH4 over suitable metal catalysts at high temperature (McCollom et al. 1999, 2010) (Figure 5.8 ).

The cell membrane , and origin of life scenarios 8E8T4LW
It is known that straight-chain amphiphiles and various biological lipids will spontaneously self-assemble under the appropriate conditions of pH, temperature, and solute concentration to form aggregates known as micelles or vesicles, which in some cases are able to trap various solutes for extended periods of time (Deamer and Barchfeld 1982). These properties have led to suggestions that such materials may have been important for the self-assembly of the earliest protocells (Szostak 2001). Intriguingly, the straight-chain fatty acids found in carbonaceous chondrites to date are just at the threshold of the types of molecules that are known to display this behavior (Monnard et al. 2002), and even these are present in very low abundance (Yuen and Kvenvolden 1973). For example, the octanoic acid content of 1 g of the Murchison meteorite would need to be dissolved in a few tens of nanoliters of water in order to form vesicles (given a critical vesicle concentration [the concentration above which bilayered or higher aggregated lipid structures form spontaneously] of 130 mM [Apel et al. 2002] and a mean abundance of 0.01 μmol g−1 in a typical meteorite [Lawless and Yuen 1979]). Nevertheless, organic solvent extracts of the Murchison meteorite show the presence of compounds that spontaneously assemble into boundary structures (Deamer 1985) (Figure 5.7c), though it is unlikely these have much compositional similarity to biological membranes.

Sources of membrane building blocks
Long-chain hydrocarbons can be formed from carbon monoxide and hydrogen in the presence of certain metals at high temperatures. Deep sea hydrothermal vents have been cited as a potential source of the energy required to synthesize prebiotic molecules, including the building blocks of membranes. Fatty acids and fatty alcohols have been synthesized under these conditions. These fatty acids will combine with ethylene glycol to form ethylene glycolyl alkanoates and bis-alkanoates, or will combine with glycerol to form monoacylglycerols and diacylglycerols.  Others have suggested that the first membranes consisted of highly branched polyprenyl chains, instead of alkyl chains. However, it is unlikely that the starting material would be at sufficient concentrations  and it also unlikely that the required phosphorylating agents would have been available on early Earth.

Vesicle assembly
Even if membrane building blocks were present in sufficient quantities, specific concentrations and other environmental conditions are required for assembly. All possible components other than fatty acids have been eliminated from contention for a lack of plausible synthetic pathways. The assembly of fatty acids into lipid bilayers is dependent upon the chain length, concentration, pH, and temperature. Short chain fatty acids form vesicles at room temperature when the pH is within half a pH unit of the pKa of the acid. Longer chain fatty acids require higher temperatures (30-70°C).15, 16 In addition, the concentration of fatty acids must be quite high (130 to 20 mM) for vesicles to form.17 The presence of such high concentrations of fatty acids would be unlikely on the primordial earth. Some of the exacting conditions can be moderated by the presence of fatty alcohols with the same hydrocarbon chain length as the fatty acid.7, 16 However, the molar ratio must be almost exactly 10:1 (acid:alcohol) in order for any significant effect to be seen.18 In addition to temperature, pH, and concentration requirements, vesicle formation is highly dependent upon ionic strength and the presence of certain ions. Thus, the presence of sodium chloride at levels found in the oceans of primordial earth causes vesicles to aggregate into sheets, and the presence of Ca+2, Mg+2, Fe+2 at primordial concentrations causes fatty acids to precipitate.

The spontaneous formation of bilayer vesicles  is dominant explanation for the appearance of membranes, but is not without challenging problems. It has been shown that fatty acids will spontaneously form phospholipids in the presence of glycerol and phosphates when heated to dryness.  However,  it would be extremely unlikely that nature would produce all three chemicals in the same location and then heat them to dryness. 

Encapsulation and transport
The mere formation of an enclosed vesicle is not sufficient to guarantee functionality. In order to be useful as a mechanism involved in the naturalistic origin of life, membranes must encapsulate materials necessary to initiate life and be able to transport material in and out of the boundary. Modern biological membranes contain protein systems that actively and passively allow the exchange of nutrients and wastes. Since these transport systems would not be available on the primordial earth, other systems must have existed to make the process even remotely feasible. Despite the extremely unlikely appearance of phospholipid membranes under early-earth conditions, most studies that have examined encapsulation have used such membranes. Encapsulation of primitive fatty acid membranes would have to involve repeated rupture and resealing (through agitation) during periods of changing osmotic gradients (increasing and decreasing salt concentrations). Changing the concentrations of solutes would have the additional problem of likely altering pH, which would disrupt the exacting conditions required for fatty acid membrane assembly. The presence of locations where these exact conditions would exist would be very limited on the primordial earth. In addition, in order for some form of life to be created in this manner, both a primitive replicator and metabolic system must be encapsulated at this time. Of course, such systems would both encapsulate and release materials on each cycle, and it is unclear what kind of equilibrium would be eventually achieved.

Once a stable membrane is formed, some kind of transport system for nutrients/wastes would be required to maintain the metabolism of the proto-cell. Passive transport systems would be the easiest to form, but such systems would automatically achieve equilibrium, making further transport impossible. Obviously, due to their complexity, active transport systems would not be expected to be encoded by a primitive replicator.

Energy acquisition
Possible sources of energy for proto-cells are heat energy, chemical energy, and light energy. However, none of these forms of energy harvest are compatible with a primitive fatty acid membrane in the presence of known prebiotic chemicals present in the environment. This is because carboxyl head group of a fatty acid membrane mediates proton permeability, eliminating the possibility of generating a proton gradient. The only way to get around this problem was to use an oleate-arginine system, which slowed the decay of the gradient. However, the unsaturated oleate would not have been present in a prebiotic environment. In addition, the system was inhibited by alkali cations, which would have been present in early earth environments.

The capture of light energy by proto-cells has been hypothesized to occur through encapsulated iron compounds or polycyclic aromatic hydrocarbons (PAH), which absorb light in the near-UV and blue wavelengths.14, 23 While ferrocyanide and PAH may have been present on early earth, these compounds cannot generate a proton gradient when enclosed within fatty acid membranes.

Growth and Division
Primitive membranes must have the ability to grow and replicate without the aid of biomolecular machinery in order to function in a hypothesized proto-cell.25 Slow addition of myristoleate micelles to a myristoleic acid/myristoleate vesicle system results in 90% of the added fatty acid was incorporated into the original vesicles, causing them to grow.25 Others have used osmotically swollen oleate vesicles to cause growth through vesicle-vesicle fusion.22 However, since the presence of these unsaturated fatty acids on early earth is unlikely, the relevance of these studies to the origin of life is questionable. When considered in the context of an RNA world scenario, the requirement for the presence of divalent cations by ribozymes would result in the precipitation of fatty acids, disrupting membranes. Division of membranes may occur when they reach a certain size.26 The ability of this to occur is dependent upon the size of the membrane and it composition. However, since the studies were done only with unsaturated fatty acid membranes, it is unclear what relevance there would be to the fission of saturate fatty acid membranes under early earth environments.

Unrealistic studies
Besides the problem that most origin of membranes studies have examined membranes composed of materials that would have never existed on the primordial earth, there is an even more fundamental problem that tends to plague virtually all origin of life research. Once a compound has been declared "prebiotic", researchers immediately begin using the highly purified product at exceptional concentrations. According to Robert Shapiro:

"The observation of a specific organic chemical in any quantity (even as part of a complex mixture) in one of the above sources would justify its classification as "prebiotic," a substance that supposedly had been proved to be present on the early Earth. Once awarded this distinction, the chemical could then be used in pure form, in any quantity, in another prebiotic reaction. The products of such a reaction would also be considered "prebiotic" and employed in the next step in the sequence."27

The origin of biological membranes, like the origin of replication and metabolism, is fraught with problems and invokes extremely improbable chemistry. Although some of the building blocks of potential membranes might have been synthesized on early earth, the ones used in modern biological membranes (phospholipids) could not have been. Therefore, one must hypothesize some kind of primordial membrane that was later discarded in favor of modern membranes. However, even this scenario suffers from insurmountable problems. The extraterrestrial synthesis and delivery of membrane building blocks remain unproved. Although such materials might have been synthesized near hydrothermal vents in the early seas, the assembly of such materials is quite problematic. Conditions requiring high concentrations, exact pH and temperature, plus the absence of high sodium and small amounts of certain metal ions, prevents the assembly of such components within the earth's early oceans. Conditions that might concentrate fatty acids to sufficient levels to form membranes would also concentrate solutes that disrupt the formation of those membranes. Encapsulation of a proto-cell replicator and metabolic system would be quite problematic, since the conditions that would encourage such activity would likely lead to conditions that would disrupt the primitive membrane completely. Primitive membranes must be able to transport nutrients and wastes, although passive transport systems would readily reach equilibrium and active transport systems would not be expected to be produced immediately upon encapsulation. Energy acquisition is problematic, since fatty acids membranes cannot generate a proton gradient. Membranes composed of unsaturated fatty acids or phospholipids can generate proton gradients, but would not be expected to have existed in early earth environments. Virtually all studies that have examined membrane growth and division have used unsaturated fatty acid membranes, which would not have been present on the early earth. Because of this problem, these studies have questionable relevance to the origin of life on earth.


The fact that all contemporary living cells are defined by lipid-bilayer membranes suggests that protocellular structures could be modeled in the laboratory by dispersing lipid molecules as bilayer vesicles in aqueous phases . However, the use of lipid bilayers for this purpose has a significant drawback, which is their relative impermeability to polar or ionic molecules. To overcome this permeability barrier, complex protein transport systems have evolved in all contemporary cells  which were presumably absent in early cells.

As if cells would function without the protein transport systems.... and just wait their evolution and appearance to take over...... 

Therefore, the latter necessarily relied on simple transport mechanisms such as passive diffusion across bilayer membranes to take up nutrients and sources of chemical energy from the environment.

The just so story is remarkable... why should someone buy to it ? where  is the evidence to back up the claim ? We don't know, therefore lets just make up a story ? And when we add adjectives, like probable, possible, most likely etc.... the story becomes highly compelling......

What solutes might have been important to early cellular life? Several obvious examples include phosphate, simple carbohydrates like glyceraldehyde, and perhaps amino acids. Of these, phosphate and amino acids are ionic, and bilayer membranes have been shown to represent significant permeability barriers to their free diffusion. 

Membrane self-assembly processes: Steps toward the first cellular life   3

Some form of compartmentation is a necessary prerequisite for maintaining the integrity of interdependent molecular systems that are associated with metabolism, and for permitting variations required for speciation. The fact that lipid-bilayer membranes define boundaries of all contemporary living cells suggests that protocellular compartments were likely to have required similar, self-assembled boundaries. Amphiphiles such as short-chain fatty acids, which were presumably available on the early Earth, can self-assemble into stable vesicles that encapsulate hydrophilic solutes with catalytic activity. Their suspensions in aqueous media have therefore been used to investigate nutrient uptake across simple membranes and encapsulated catalyzed reactions, both of which would be essential processes in protocellular life forms.

The emergence of life on the early Earth required the presence of at least three different substances and related physical properties: liquid water, a source of free energy, and organic compounds capable of self-assembly. Liquid water is essential for all life today, and it is highly implausible that life can exist in its absence. Possible energy sources include sunlight (if life began on the Earth's surface) and energy arising from chemical disequilibria in submarine or subterranean sites. Self-assembling compounds must have been available to provide building blocks for polymer synthesis and formation of boundary structures.

In contemporary cells, a fundamental role of membrane boundaries is to provide a selective permeability barrier that is necessary for separating the cytoplasm from the external environment. The transmembrane transport of nutrients and ionic solutes is mediated by a variety of membrane-associated proteins that act as channels, carriers, and active transporters (pumps). Membrane receptors provide a sensor mechanism that permits communication between the intracellular milieu and the outside world. Membranes also capture light energy and redox energy by using pigment systems and electron transport to generate electrochemical proton gradients as a source of free energy.

As we learned more about the role of membranes in defining cell structures, it became clear that all membranes incorporated lipid bilayers as the primary permeability barrier, and that phospholipid is a nearly ubiquitous amphiphilic component of the bilayer.  Lipid bilayer vesicles are commonly referred to as liposomes, and such self-assembled membrane structures can be used as models of the earliest cell membranes. Several early papers demonstrated that phospholipids could be synthesized under simulated prebiotic conditions from mixtures of fatty acids, glycerol, and phosphate.   However, the simultaneous presence of all three components on the early Earth is highly speculative, and we have therefore turned our attention to simpler membranogenic amphiphiles.  

Stability and Permeability of Amphiphile Vesicles
Although the ability of phospholipids to self-assemble into membranous vesicles is common knowledge, it is less well known that a variety of membranous structures can also be prepared from single-chain amphiphiles such as fatty acids fatty alcohols, and monoglycerides. We will argue that such vesicles are plausible models for the formation of early cellular compartments.

Although the composition of the membrane-forming amphiphiles present in the Murchison organic mixture has not yet been established in detail, it is clear that substantial amounts of monocarboxylic acids are present . For this reason we have begun to investigate the physical properties of self-assembled structures produced by monocarboxylic acids of various chain lengths, and of mixtures with other simple amphiphilic compounds. Gebicki and Hicks (1973, 1976) first established that oleic acid, a fatty acid, forms vesicular structures. Since this discovery, the bilayer-forming potential of fatty acids with shorter hydrocarbon chains (C8-C11) has been investigated . The length and the degree of unsaturation of the hydrocarbon chains play an important role in determining the bilayer-membrane properties, such as permeability and stability, which would have been essential for the primitive life forms.

1. http://complex.upf.es/~andreea/2006/Bib/MonnardDeamer.NutrientUptakeByProtocells.pdf
2. http://www.godandscience.org/evolution/origin_membranes.html
3. http://onlinelibrary.wiley.com/doi/10.1002/ar.10154/full
4. ASTROBIOLOGY An Evolutionary Approach,  page 97
5. The Cell, Panno, page 18
6. https://sci-hub.ee/10.1098/rstb.2007.2065

Last edited by Otangelo on Sun May 01, 2022 8:34 am; edited 2 times in total




How are lipids synthesized?

Lipids play a life essential role, and so, in many biochemical and cell biological processes. They are involved in the formation of biological membranes and therefore are important elements of organelle biogenesis and function. 25 This is not only true for bulk lipids such as the major classes of glycerophospholipids, sterols, and sphingolipids, but also for less abundant lipid species. Lipids with only minor concentrations in cells have more subtle functions. For example, polyphosphoinositides, lysophospholipids, or ceramides are essential for signaling processes. Certain classes of lipids, such as sphingolipids, are also sensors of cellular stress (heat shock) and important components for signal transduction. These lipids provide the appropriate environment for membrane proteins to function as enzymes or transporters, or to act as positive regulators of enzymes to gain optimum activity in membranes.

Many regulatory phenomena caused by lipids, which have not been recognized before, became evident through the advance of molecular biological research. Intracellular lipid transport and distribution play an important role in the maintenance of cellular structure and function. The lipid composition of vesicles involved in membrane traffic, recently, turned out to be a most important parameter for protein targeting. For example, the presence of sterols and sphingolipids in secretory and endocytotic vesicles appears to be essential. Membrane contact, as a mechanism of translocation of components between subcellular compartments, may also depend on the lipid patterns of donor and acceptor membranes.

Lipid metabolism must not be regarded only as an isolated process, but rather as a part of total cellular metabolism, which is highly linked to other metabolic and cell biological pathways

The first step in lipid metabolism is the hydrolysis b of the lipid c in the cytoplasm to produce glycerol and fatty acids. 5

Complex lipids consist of backbone structures to which fatty acids d are covalently bound. Principal classes include the glycerolipids, for which glycerol is the backbone, and sphingolipids, which are built on a sphingosine backbone. The two major classes of glycerolipids are glycerophospholipids and triacylglycerols

Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. They are the main component of biological membranes.

The phospholipids, which include both glycerophospholipids and sphingomyelins, are crucial components of membrane structure. Different organisms possess greatly different complements of lipids and therefore invoke somewhat different lipid biosynthetic pathways. For example, sphingolipids and triacylglycerols are produced only in eukaryotes. In contrast, bacteria usually have rather simple lipid compositions. 

The cell membrane , and origin of life scenarios 0jSRAa2
Glycerolipid metabolism 12

Glycerol, essential for life
Glycerol a also called glycerine or glycerin is a simple polyol j compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in all lipids known as triglycerides. 8 Glycerin is a trihydroxy sugar alcohol that is an intermediate in carbohydrate and lipid metabolism. 9

The phospholipids characteristic of contemporary membranes are composed of two fatty acids esterified to a glycerol phosphate molecule, with any of several groups also attached to the phosphate through an ester bond, such as
choline, ethanolamine, serine, and glycerol. 7 Although hydrocarbons are abundant on today’s Earth, they are primarily products of biological processes, so there must have been supposedly abiotic sources of the amphiphiles required for assembly into first membrane structures if natural membrane assembly mechanisms are presupposed. Two possibilities are geochemical synthesis under volcanic conditions and delivery during the accretion of asteroids and comets in the late stage of planet formation.

Of course, that raises the question, why would biological processes have evolved the ultracomplex protein-machine-based processes to make lipids, if they were supposedly readily available on early earth? 

Phospholipids found in cell membranes show a wide range of chemical variability. Their head groups typically consist of a phosphate group bound to a glycerol (glycerin) backbone. 1
Cell membranes basically consist of phospholipids, which are amphiphile ( water-loving) molecules, that is to say that they possess a hydrophilic ( attracted to water ) head (consisting of glycerol-phosphate) and a hydrophobic ( repelling water )  tail (which may belong fatty acids or isoprenoid derivatives) 2 The fundamental distinction (with no known exceptions) between the phospholipids of the bacteria and eukaryotes, and those of the archaea rests in the type of stereoisomer e of glycerol used  ; 

glycerol-3-phosphate in the bacteria and eukaryotes, 
glycerol-1-phosphate in the archaea. 

The pathways by which these two stereoisomers are synthesized are so different that, for certain authors, the cenancestor did not have membranes and was an acellular organism or, according to yet others, it had mineral membranes consisting of iron monosulfide.

Here we have one reason amongst many others, why common ancestry of all three domains of life is extremely unlikely. 

The idea of an ancestor without lipid membranes, however, comes up against one piece of evidence: there are membrane proteins that are universally conserved, like the ATPase. A less radical hypothesis, which had recently been supported by molecular phylogeny analyses, would be to imagine a cenancestor with a heterochiral membrane, that is to say possessing a mixture of phospholipids constructed with glycerol-1-phosphate and glycerol-3-phosphate. Additional molecular phylogenetic studies further support the idea that the cenancestor had a complete toolkit to make phospholipids of either fatty acids or isoprenoid chains. Evolution would have subsequently led to opposite stereospecificity and choice of lateral chains in the bacteria and in the archaea.

Another explanation is that common ancestry is an unlikely hypothesis, and the origin of the three domains of life is not due to a last common universal ancestor, but distinct creation events. 

The phospholipids of Bacterial and eukarya plasma membranes consist of fatty acids ester-linked f to glycerol-3-phosphate
Archaea make theirs of isoprenoids ether-linked g to glycerol- 1-phosphate

The cell membrane , and origin of life scenarios PxvG9L6
The structure of membrane phospholipids in the three domains of life. 
The type of stereo-isomer of glycerol-phosphate distinguishes, with no known exception, between the phospholipids of bacteria and eukaryotes, and those of the archaea: glycerol-3-phosphate in bacteria and eukaryotes, glycerol-1-phosphate in archaea. Other differences are observed in the hydrophobic chains and the bond between the latter and the glycerol-phosphate, but there are exceptions. Some phospholipids in archaea have chains of fatty acids, and some phospholipids in bacteria include ether bonds.

Glycerol 1-phosphate, sometimes called as D-glycerol 3-phosphate, is an enantiomer of glycerol 3-phosphate. Most organisms use 3-phosphate, or L-configuration, for glycerolipid backborn; however, 1-phosphate is specifically used in archeal ether lipids.

Glycerol 3-phosphate is a phosphoric ester of glycerol, which is a component of glycerophospholipids. 11

Glycerol 3-phosphate synthesis and metabolism

There are several routes to synthesize Glycerol 3-phosphate. 

1. Glycerol 3-phosphate is synthesized by reducing dihydroxyacetone phosphate (DHAP), a glycolysis intermediate, with glycerol-3-phosphate dehydrogenase. 11
Glycerol-3-phosphate dehydrogenase is an enzyme that catalyzes the reversible redox conversion of dihydroxyacetone phosphate  to sn-glycerol 3-phosphate. Glycerol-3-phosphate dehydrogenase serves as a major link between carbohydrate metabolism and lipid metabolism. Sn-glycerol-3-phosphate dehydrogenase (GlpD) 4 is an essential membrane enzyme, functioning at the central junction of respiration, glycolysis, and phospholipid biosynthesis. Its critical role is indicated by the multitiered regulatory mechanisms that stringently controls its expression and function. Once expressed, GlpD activity is regulated through lipid-enzyme interactions. Homologs of GlpD are found in practically all organisms, from prokaryotes to humans, with >45% consensus protein sequences, signifying that these structural results on the prokaryotic enzyme may be readily applied to the eukaryotic GlpD enzymes.

Despite the pioneering work of Hargreaves et al. in 1977 who demonstrated that the synthesis of phosphatidic acid and other lipids could be achieved abiotically, it is considered very improbable that fatty acids, glycerol, and phosphate (i.e., the standard molecular components of a phospholipid) could have been present together in high enough concentrations on the primordial Earth. 6

The cell membrane , and origin of life scenarios 5UaWrn1

2. Glycerol can be a source for glycerol-3-phosphate, in which case, a phosphate from ATP is transferred to glycerol by glycerol kinase forming glycerol-3-phosphate and ADP. 22 Glycerol kinase 23 catalyzes the phosphorylation i of glycerol to form glycerol-3-phosphate, which is then acylated at both the 1- and 2-positions to yield phosphatidic acid. Glycerol is a precursor for the synthesis of phospholipids. Before glycerol can enter the pathway of glycolysis or gluconeogenesis (depending on physiological conditions), it must be converted to their intermediate glyceraldehyde 3-phosphate in the following steps:

The cell membrane , and origin of life scenarios Api38dK

The cell membrane , and origin of life scenarios CMRsb09
Glycerol kinase, encoded by the gene GK, is a phosphotransferase enzyme involved in triglycerides and glycerophospholipids synthesis. 

The cell membrane , and origin of life scenarios 894D71f

b Biological hydrolysis is the cleavage of biomolecules where a water molecule is consumed to effect the separation of a larger molecule into component parts. 13

c In biology, a lipid is a biomolecule that is soluble in nonpolar solvents. Non-polar solvents are typically hydrocarbons used to dissolve other naturally occurring hydrocarbon lipid molecules that do not (or do not easily) dissolve in water, including fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, and phospholipids. 14

In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28. 15

e In stereochemistry, stereoisomers are isomeric molecules that have the same molecular formula and sequence of bonded atoms (constitution), but differ in the three-dimensional orientations of their atoms in space 16

f In chemistry, an ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH (hydroxyl) group is replaced by an –O–alkyl (alkoxy) group 17

g In an organic chemistry general sense, an ether lipid implies an ether bridge between an alkyl group (a lipid) and an unspecified alkyl or aryl group, not necessarily glycerol. 18

h  Isoprenoids are any of a class of organic compounds composed of two or more units of hydrocarbons, with each unit consisting of five carbon atoms arranged in a specific pattern. These compounds are derived from five-carbon isoprene units and are biosynthesized from a common intermediate known as mevalonic acid, which is itself synthesized from acetyl-CoA. These lipids are considered to be the largest group of natural products, playing a wide variety of roles in physiological processes of plants and animals. 19

In chemistry, phosphorylation of a molecule is the attachment of a phosphoryl group. Together with its counterpart, dephosphorylation, it is critical for many cellular processes in biology. 21

polyol is an organic compound containing multiple hydroxyl groups. 24

1. Origins of life : biblical and evolutionary models face off / Fazale Rana & Hugh Ross., page 102
2. Young Sun, Early Earth and the Origins of Life , page 122
3. https://ipfs.io/ipfs/QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco/wiki/Glycerol_3-phosphate.html
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2265192/
5. http://chemistry.elmhurst.edu/vchembook/622overview.html
6. Prebiotic Systems Chemistry: New Perspectives for the Origins of Life : http://sci-hub.tw/https://pubs.acs.org/doi/10.1021/cr2004844
7. http://sci-hub.tw/10.1016/j.resmic.2009.06.004
8. https://en.wikipedia.org/wiki/Glycerol
9. https://pubchem.ncbi.nlm.nih.gov/compound/glycerol
10. https://en.wikipedia.org/wiki/Glycerophospholipid
11. https://en.wikipedia.org/wiki/Glycerol_3-phosphate
12. https://www.genome.jp/kegg-bin/show_pathway?map00561
13. https://en.wikipedia.org/wiki/Hydrolysis
14. https://en.wikipedia.org/wiki/Lipid
15. https://en.wikipedia.org/wiki/Fatty_acid
16. https://en.wikipedia.org/wiki/Stereoisomerism
17. https://en.wikipedia.org/wiki/Ester
18. https://en.wikipedia.org/wiki/Ether_lipid
19. https://en.wikibooks.org/wiki/Structural_Biochemistry/Lipids/Isoprenoids
20. https://en.wikipedia.org/wiki/Phosphatidic_acid
21. https://en.wikipedia.org/wiki/Phosphorylation
22. http://reactome.org/content/detail/R-HSA-75887
23. https://en.wikipedia.org/wiki/Glycerol_kinase
24. https://en.wikipedia.org/wiki/Polyol
25. Lipid Metabolism and Membrane biogenesis, page 1





The cell membrane , and origin of life scenarios Sem_me10




Carbohydrates ( carbo = carbon + hydro = water ) are a result of the chemical bonding of Hydrogen, Oxygen, and Carbon atoms.  Steve Benner (2010): Carbohydrates have a ratio of 1:2:1 and an aldehyde or ketone group 1. They are subdivided into monosaccharides ( simple sugars, normally containing 3 to 7 sugars), disaccharides ( two monosaccharides joined together), and polysaccharides ( long chains of monosaccharides joined together).

The most common carbohydrates are six-carbon (hexose) and five-carbon (pentose) sugars. Carbohydrates are the building blocks of RNA and DNA, and as such, their origin on early earth is of fundamental importance for the origin of life questions. Their six-carbon versions, like glucose, are also an important source of energy through oxidation. Most carbon used in biology today is sourced by photoautotrophs like cyanobacteria that fix carbon dioxide CO2 using the energy from the sun through photosynthesis and they synthesize sugars like glucose.   

Geoffrey Zubay, Origins of Life on the Earth and in the Cosmos (2000): In the prebiotic world, it seems likely that one-carbon chemistry also dominated the synthesis of carbon compounds that were crucial to the origin of life. However, in this case, the key precursor carbon was probably formaldehyde (CH2O) formed in the atmosphere or in the lithosphere. Formaldehyde always has been considered to be the most likely precursor of carbohydrates in the prebiotic world. It has the advantage that it is a high-energy compound for which routes of synthesis in the atmosphere have been found. A major stumbling block for a long time was that no feasible routes from formaldehyde to ribose had been found. Yields always were very small and ribose always constituted a very minor component of the mixture of sugars that were usually formed. In the 1860s Butlerov discovered that when an aqueous solution of formaldehyde is warmed in the presence of a calcium hydroxide suspension, a mixture of sugars is produced. The process is referred to as the formose reaction.  The formose reaction starts from a concentrated solution of formaldehyde (usually 1 to 2%). Within a matter of minutes at temperatures around 55°C a broad array of sugars and other products is formed. Could this procedure be used without modification for the prebiotic synthesis of ribose? This is very unlikely because ribose usually constitutes 1% or less of the reaction products. 2

J. Oró (1990): Under the slightly basic conditions of the Butlerow synthesis, a complex mixture of more than 50 different pentoses, hexoses,  and many other sugars is obtained. Furthermore, under the reaction conditions in which it is formed, ribose tends to decompose. Accordingly, at the present time it is difficult to understand how ribose could have accumulated and  separated from other sugars of abiotic origin in the prebiotic environment into acidic compounds 3

Carl Sagan (1992) Sources of organic molecules on the early Earth divide into three categories: delivery by extraterrestrial objects; organic synthesis driven by impact shocks; and organic synthesis by other energy sources (such as ultraviolet light or electrical discharges). Estimates of these sources for plausible end-member oxidation states of the early terrestrial atmosphere suggest that the heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources. 6

Carbohydrates come in left, and right-handed chiral forms. Ribose, the backbone of RNA and DNA, is right-handed. Kitadai (2017) mentions and lists several scientific papers that deal with problems that have been recognized for ribose synthesis via the formose reaction 4 

The three-carbon glycerol backbone in phospholipids in archaea is 'right-handed', but left-handed in all other organisms, where they are only used in the right-handed form.

Extraterrestrial sources
R.Shapiro (2007) Some writers have presumed that all of life’s building could be formed with ease in Miller-type experiments and were present in meteorites and other extraterrestrial bodies. This is not the case. A careful examination of the results of the analysis of several meteorites led the scientists who conducted the work to a different conclusion: inanimate nature has a bias toward the formation of molecules made of fewer rather than greater numbers of carbon atoms, and thus shows no partiality in favor of creating the building blocks of our kind of life. (When larger carbon-containing molecules are produced, they tend to be insoluble, hydrogen-poor substances that organic chemists call tars.) I have observed a similar pattern in the results of many spark discharge experiments. 46

Daniel P. Glavin (2018): Asteroids, comets, and their fragments including meteorites, micrometeorites, and interplanetary dust particles (IDPs) also serve as delivery vehicles for organic matter. At present, about 4 ~x 10^7 kg of extraterrestrial material, ranging in size from meter-sized meteorites down to micron-sized IDPs, rain down on the Earth every year.  Therefore, exogenous delivery may have been an important source of organic carbon on the early Earth including complex prebiotic molecules available for the origin of life 7

The narrative is well exposed in the recapitulation and closing thoughts of Maheen Gull's paper (2021):
" There is a strong possibility of the emergence of life on the early Earth as a consequence of the abiotic synthesis of organic molecules via interstellar chemical reactions and their subsequent delivery to early Earth via meteoritic bombardments, followed by concentration, self-assembly reactions catalyzed by the minerals present on the early Earth, and finally the proliferation of the early life on the Earth." 11

DANIEL SEGRÉ (1999): Assuming that a significant amount of the organic substances in cometary and meteoritic infall survived atmospheric entry, most of the material would presumably enter the oceans and be released over a period of many years. One mechanism for the release of organic components from extraterrestrial infall is thermal extraction. Primordial membranes would need to continuously add amphiphilic components in order to accommodate the growth and replication of the encapsulated macromolecular system or of the lipid aggregate itself. The challenge is to find a plausible synthetic pathway for hydrocarbons with 10 or more carbons in their chains. Such chains must also have modifications, e.g. chain branching, that will allow them to be fluid at the permissive environmental temperature. 35

Much is made of the Murchison meteorite. Here's a quick calculation: Assuming no contamination from its collision with earth, then "sugar-related" compounds were measured at 60 parts per million (ppm), about the same as amino acids (quotes, because not all are related to biology and all, are racemic). Using a small amino acid-like alanine (MW=89 g/mol) and assuming you would need at least 0.1 Molar concentration in the ocean (V=1.35^21 Liters) to get peptides, then the mass of meteorites to deliver enough alanine would be 2^26 g. (The mass of the earth is about 6^24 kilograms, so 6^27 grams). The Murchison weighs about 100 kg. Thus the earth would've been struck by 2^21 meteorites the size of Murchison. The age of the earth is about 1.5^17 seconds. Thus 13,000 meteorites would have to strike every second of Earth's existence. That's a far stretch to be plausible. 12

Kepa Ruiz-Mirazo (2013): Both long-chain monocarboxylic acids and polycyclic aromatic hydrocarbons (PAHs) with amphiphilic properties were extracted from the Murchison meteorite. Deamer et al. have shown that these materials are able to form vesicle-like structures under specific conditions. Their formation could have occurred by irradiation of interstellar matter with UV light, as revealed by experimental irradiation of simulated cometary and interstellar ice. 36

In 2012, ScienceDaily reported that:  "researchers at NASA's Jet Propulsion Laboratory are creating concoctions of organics, or carbon-bearing molecules, on ice in the lab, then zapping them with lasers. Their goal: to better understand how life arose on Earth."  The abstract of the paper reported, started with this:

Understanding the evolution of organic molecules in ice grains in the interstellar medium (ISM) under cosmic rays, stellar radiation, and local electrons and ions is critical to our understanding of the connection between ISM and solar systems. Our study is aimed at reaching this goal of looking directly into radiation-induced processing in these ice grains. 9

So what did they produce? Murthy S. Gudipati writes: The organics looked at in the study are called polycyclic aromatic hydrocarbons, or PAHs for short. These carbon-rich molecules can be found on Earth as combustion products: for example, in barbecue pits, candle soot and even streaming out of the tail pipe of your car. They have also been spotted throughout space in comets, asteroids and more distant objects. 8 That has hardly something to do with organic building blocks to start life.  

A factory requires a building, that protects all its workers, manufacturing processes, machines, etc. from the hostile external conditions of the environment ( rain, storms, winds, etc.) and acts like a security guard -  that only lets certain things enter and leave the cell/factory, makes sure wanted things the factory needs come in and makes sure unwanted things that would be detrimental/ harmful to the factory don't enter, and that controls the right internal conditions. A factory is also subdivided into different compartments for labor division.  

The first life form must have had membranes with similar active stratagems. Cell membranes control what substances can go in and out, like nutrients and ions, using various transport mechanisms. It also hosts proteins that permit cell communication through signaling. Biological cell membranes are essential for internal compartmentalization, in special in eukaryotic cells, which are far more complex than prokaryotes. Cell membranes also form energy gradients - which are necessary to generate energy, similar to a hydroelectric energy factory, that needs a dam ( The cell membrane can act as a dam, enabling the energy gradient). Cell membranes are furthermore essential to keeping a homeostatic milieu (pH, fluid balance, cell size control etc.) Cell membranes, cell proteins, and an internal homeostatic milieu form an interdependent system, that had to be fully functional. All at once. A gradual emergence would produce non-functional intermediate states of affairs.

Lipids can be distinguished between mono - or diacyl glycerols (“incomplete lipids”, ILs) or phospholipids (“complete lipids”, CLs). 28 

The cell membrane , and origin of life scenarios Osc_mi11
All unstructured text is available under the Creative Commons Attribution-ShareAlike License;

Their head groups typically consist of a phosphate group bound to a glycerol backbone. They link to the tails that are usually long, linear fatty acids. These chains have normally a length of between sixteen to eighteen carbon atoms. In the picture, there are two different fatty acids, one saturated and one unsaturated, bonded to the glycerol molecule. The unsaturated fatty acid has a slight kink in its structure due to the double bond.

David W. Deamer (2010): In contemporary cells, a fundamental role of membrane boundaries is to provide a selective permeability barrier that is necessary for separating the cytoplasm from the external environment. The transmembrane transport of nutrients and ionic solutes is mediated by a variety of membrane-associated proteins that act as channels, carriers and active transporters (pumps). Membrane receptors provide a sensor mechanism that permits communication between the intracellular milieu and the outside world. Membranes also capture light energy and redox energy by using pigment systems and electron transport to generate electrochemical proton gradients as a source of free energy. All of these functions require membrane-associated proteins which were presumably absent in the first forms of cellular life. It, therefore, seems likely that the membrane boundaries of the earliest cells simply provided a selective permeability barrier that permitted the permeation of essential nutrients but retained polymeric products of primitive biosynthesis. 19

Martin M Hanczyc: (2017): The membrane defines the unit cell and its internal volume. This barrier also acts to preserve the integrity of the cell in varying environments. But membranes are more than just passive containers. They mediate the interactions of cells with the environment including the harvesting of energy, material, and other resources, and the interaction with other cells including potential pathogens. Such functionalities are essential mechanisms for cells to avoid equilibrium and death. The material and informational flux through a cell is often controlled by various proteins and lipid conjugates integrated into the membrane. For example, transmembrane proteins govern signal transduction pathways. 5 19

Cell (cytoplasmic) membranes are made of phospholipids, which are made of fatty acids attached to a glycerol backbone. Their polar head group makes them amphiphilic (water-loving) on the outside, and their fatty acid tail is hydrophobic ( water-repelling). They form spontaneously bilayers in aqueous environments.  Today's cell membranes form with all the membrane proteins an enormously complex system. Scientific hypotheses are that they are the product of spontaneous formation, self-assembling structures, or due to a long period of evolution, being preceded by simpler systems, but there is no consensus on what such supposed "proto-cell" membranes could have looked like. Is the emergence through a gradual process plausible?

Saturated vs unsaturated 
Membrane fluidity is life-essential.  A.J.M.Driessen (2014): A vital function of the cell membrane in all living organisms is to maintain the membrane permeability barrier and fluidity. 32 S.Ballweg (2016): The maintenance of a fluid lipid bilayer is key for membrane integrity and cell viability. 33 

David Deamer (2017): Saturated hydrocarbon chains would “freeze” into gels at ordinary temperature ranges, so adding unsaturated cis double bonds near the center of the chain solves this problem. 37

Libretext: In their saturated form, the fatty acids in phospholipid tails are saturated with bound hydrogen atoms; there are no double bonds between adjacent carbon atoms. This results in tails that are relatively straight. In contrast, unsaturated fatty acids do not contain a maximal number of hydrogen atoms, although they do contain some double bonds between adjacent carbon atoms; a double bond results in a bend of approximately 30 degrees in the string of carbons. Thus, if saturated fatty acids, with their straight tails, are compressed by decreasing temperatures, they press in on each other, making a dense and fairly rigid membrane. If unsaturated fatty acids are compressed, the “kinks” in their tails elbow adjacent phospholipid molecules away, maintaining some space between the phospholipid molecules. This “elbow room” helps to maintain fluidity in the membrane at temperatures at which membranes with saturated fatty acid tails in their phospholipids would “freeze” or solidify. The relative fluidity of the membrane is particularly important in a cold environment. A cold environment tends to compress membranes composed largely of saturated fatty acids, making them less fluid and more susceptible to rupturing. Many organisms (fish are one example) are capable of adapting to cold environments by changing the proportion of unsaturated fatty acids in their membranes in response to the lowering of the temperature. 30

Besides helping maintain fluidity, unsaturated lipids help decrease sensitivity to oxidative degradation of lipids and help increase lifespan. 

Homeoviscous adaptation
The bilayer cell membrane is unstable unless sophisticated mechanosensing and signaling pathways provide a mechanism of adaptation that controls its properties.
R.Ernst (2016): Biological membranes are complex and dynamic assemblies of lipids and proteins. Bacteria, fungi, reptiles, and fish do not control their body temperature and must adapt their membrane lipid composition in order to maintain membrane fluidity in the cold. This adaptive response was termed homeoviscous adaptation. The most common structure, the lamellar lipid bilayer, has various physicochemical properties including phase behavior, different degrees of fluidity/viscosity, membrane thickness, and bending rigidity that are determined both by the molecular composition and membrane curvature. A cell must monitor membrane properties to mount adaptive responses and maintain organelle identities. Lipids have a pivotal role in membrane remodeling processes and their biosynthesis and turnover are tightly regulated.

Eukaryotic cells and their organelles synthesize hundreds to thousands of lipid molecules differing in their molecular structures, physicochemical properties, and molar abundances. This stunning diversity derives from the combinatorial complexity of the lipid ‘building blocks’. Glycerophospholipids and sphingolipids have a modular design featuring two apolar hydrocarbon chains (or acyl chains) and a hydrophilic headgroup. The proportion of saturated and unsaturated acyl chains in membrane lipids is a key factor determining lipid packing, membrane viscosity, and water permeability. Bacteria, cyanobacteria, fungi, plants, and fish that do not control their body temperature increase the proportion of unsaturated acyl chains in membrane lipids to maintain fluidity in the cold. However, temperature is not the only factor that explains the unsaturation level of biological membranes. In homeotherms, such as mammals, large variations exist between the acyl chain profiles of several tissues, suggesting that this profile endows cellular membranes with specific properties. Thus, eukaryotic cells establish lipid gradients, with sterols and saturated acyl chains being gradually enriched along the secretory pathway at the expense of monounsaturated acyl chains.

Observe how the authors describe the Glycerophospholipids and sphingolipids having a "modular design".

Doris Berchtold (2012): As TORC2 regulates sphingolipid metabolism, our discoveries reveal a  homeostasis mechanism in which TORC2 responds to plasma membrane stress to mediate compensatory changes in cellular lipid synthesis and hence modulates the composition of the plasma membrane. The components of this pathway and their involvement in signaling after  membrane stretch are evolutionarily conserved 45

Natalia Soledad Paulucci (2021): It is vitally important that bacteria maintain the fluidity of their membranes at optimal values to ensure physiological homeostasis and the integrity of all the processes that occur in them. This fluidity control process, called homeoviscous adaptation, was first demonstrated in E. coli ( Sinensky 1974) by observing that membrane fluidity remains relatively constant at various temperatures.  Underlying the process of homeoviscous adaptation is the stress-triggered catalytic activity of membrane-bound enzymes and/or membrane sensors related to signal transduction mechanisms. Thus, the membrane remodeling in composition and organization may operate as an on/off switch on the controlling mechanisms 18:0. 44

The evidence indicates that maintaining a homeostatic internal milieu independently of external environmental variations is vital, and depends on a control process of membrane fluidity ( homeoviscous adaptation ) which depends on complex membrane-bound enzymes and/or membrane sensors related to signal transduction mechanisms. That points to an interdependent, irreducibly complex system, an interplay of phospholipid biosynthesis, directed, and depending on signals transmitted by these signaling pathways. Since synthesizing unsaturated chains depends on these complex enzymatic synthesis processes that were not available prebiotically, that raises the question of how they could have emerged prebiotically. 

Membrane structures
Researchers are looking for viable primitive self-assembling membranes supposing that the early earth-hosted simple amphiphilic molecules, such as fatty acids and phospholipids. They hypothesize that might have been sufficient for the formation of primitive membranes through self-assembly. Is it?

The cell membrane , and origin of life scenarios Cell_m10
Membrane structures.
Top, an archaeal phospholipid: 1, isoprene chains; 2, ether linkages; 3, L-glycerol moiety; 4, phosphate group.
Middle, a bacterial or eukaryotic phospholipid: 5, fatty acid chains; 6, ester linkages; 7, D-glycerol moiety; 8, phosphate group. 
Bottom: 9, lipid bilayer of bacteria and eukaryotes; 10, lipid monolayer of some archaea. 
I, the copyright holder of this work, release this work into the public domain. This applies worldwide.

David Deamer (2017): An amphiphile is defined as a molecule having both a non-polar (hydrophobic or “water-fearing”)  hydrocarbon moiety ( tail)  and a polar (hydrophilic or “water-loving”) head group. The simplest amphiphiles are fatty acids having a single hydrocarbon chain and a carboxylic acid head group.  10

The cell membrane , and origin of life scenarios Phosph10
Creative Commons CC0 License

Fatty acids
Fatty acids (FA) are constituents of phospholipids that make up cell membranes. Their derivatives have also other functions in the cell, like cell signaling, and supply of energy.  

The cell membrane , and origin of life scenarios Fatty_11
Libretext: Fatty acids consist of a carboxylic acid group and a long hydrocarbon chain, which can either be unsaturated or saturated. A saturated fatty acid tail only consists of carbon-carbon single bonds, and an unsaturated fatty acid has at least one carbon-carbon double or triple bond. 29  Creative Commons Attribution-ShareAlike License;

Different membrane structures between bacteria, archaea, and eukaryotes
Archaeal phospholipids are chemically distinct from those that are present in bacterial and eukaryotic membranes; the glycerine moieties possess opposite chiralities, and the corresponding biosynthetic enzymes are either unrelated or are, at least, not orthologous 48

Jonathan Lombard (2012): Two different, albeit structurally similar, kinds of phospholipids exist in nature. Bacteria and eukaryotes have the same membrane biochemistry, with ester-linked fatty acid phospholipids that are based on glycerol-3-phosphate (G3P). These G3P phospholipids were thought to be universal, but the surprise came when pioneering studies of archaeal biochemistry showed that archaeal phospholipids are made of glycerol-1-phosphate (G1P) that is ether-linked to isoprenoid chains. This chemical disparity mirrors the use of different phospholipid biosynthesis pathways in archaea and bacteria, and in particular the use of a distinctive glycerol phosphate dehydrogenase to synthesize G1P11. When they were discovered, these archaeal pathways were considered to be unique and non-homologous to those of bacteria and eukaryotes. 

Juli Peretó (2004): The two key dehydrogenase enzymes that produce G1P and G3P, G1PDH and G3PDH, respectively, are not homologous. 47

There are often exceptions to the norm. Inversely: J.Lombard (2012): The presence of fatty acids in archaea was described several decades ago, and is often neglected, as is the presence of archaeal-like ether lipids in some bacteria 14

Eugene V. Koonin (2005) Waechtershaeuser suggests that the LUCA was a form of life that existed in two dimensions only and that could synthesize both lipid (and, implicitly, cell wall) types, followed by differential loss. Differential loss explains all of the differences between archaebacteria and eubacteria, but makes the (primitive?) LUCA the biochemically most-potent organism that ever lived, with functionally redundant parallel pathways for a plethora of essential functions (lipids, cell walls, DNA replication). 20

Eukaryotic membranes
Daniel Segré (2001): A present-day eukaryotic cell incorporates three primary classes of lipid: phospholipids, sphingolipids and sterols. When these are further differentiated with respect to head groups, hydrocarbon chains and linking bonds, hundreds of different membrane lipids can be defined. 35

J.Lombard (2012): Eukaryotic membranes have typical bacterial-like phospholipids. By contrast, the apparent conservation of the isoprenoid biosynthesis mevalonate pathway in archaea and eukaryotes, and its loss in most bacteria, could support a relationship between archaea and eukaryotes. However, recent phylogenomic analyses show that there are major differences between the archaeal and eukaryotic mevalonate pathways; archaea have the most divergent pathway, whereas eukaryotes and several bacteria appear to have retained the ancestral version. This suggests that eukaryotes inherited their membranes directly from bacteria or from a common ancestor of bacteria and eukaryotes to the exclusion of archaea. This is at odds with the classical Woesian three-domain phylogeny rooted on the bacterial branch. With regard to the eukaryotes, this phylogeny implies that the last common ancestor of archaea and eukaryotes would have had either an archaeal-like membrane that was subsequently replaced by bacterial-like phospholipids in eukaryotes, or an ancestral mixed membrane with both G1P and G3P phospholipids that evolved towards a modern archaeal-like membrane in archaea and towards a bacterial-like membrane in eukaryotes after the divergence of both lineages (the pre-cell-like model). Both options are problematic. Unless considering massive horizontal transfer of all the necessary genes, the mixed membrane model implies the less parsimonious assumption that bacterial-like membranes evolved twice from the ancestral mixed membrane, in bacteria and eukaryotes independently. The fact that no archaeal-to-bacterial membrane transition has been identified so far also undermines the hypothesis that an archaeal-like membrane was secondarily replaced in eukaryotes.  14

There are no difficulties in the hypothesis that an intelligent designer created the three domains separately, and independently, which then does remove the necessity to find plausible transition routes. 

Gáspár Jékely (2006) admitted: If one assumes that none of the two membrane forms could have evolved gradually from the other one or from a mixed membrane, the conclusion that eu- and archaebacterial membranes originated independently is inevitable. 34

Prebiotic synthesis of fatty acids
Kepa Ruiz-Mirazo (2013): The Fischer−Tropsch synthesis, which is known to produce long hydrocarbon chains from carbon monoxide and hydrogen gases in the presence of a metal catalyst at high temperatures, is considered a possible source of fatty acids and fatty alcohols. In addition to the classical results on those lines by Oró and co-workers, more recently Simoneit and coworkers have conducted this reaction by heating oxalic acid solutions at temperatures that simulate the conditions at deep-sea hydrothermal vents. At the optimal temperature (150−250 °C), the lipid components ranged from C12 to more than C33 and included n-alcohols, n-alkanoic acids, n-alkyl formates, n-alkanals, n-alkanones, n-alkanes, and n-alkenes, all with essentially no carbon number preference. 36

David Deamer (2017): For stability in an aqueous cytosol of a living cell, the hydrocarbon chains must be in the range of 14 to 18 carbons in length.  37

The fischer-Tropsch synthesis produces a varied length of hydrocarbons, and in order to have stability in aqueous cytosols, the chain must have a size of 14 to 18 carbons. That means the product is not viable.

Biotic synthesis of fatty acids
Dr. Peter Reilly: The standard way for cells to synthesize fatty acids is through the fatty acid synthesis cycle, using eight enzymes (acyl-CoA synthase, acyl-CoA carboxylase, acyltransferase, ketoacyl synthase, ketoacyl reductase, hydroxyacyl dehydratase, enoyl reductase, and thioesterase) and acyl carrier protein) 21

Differences in the biosynthesis of fatty acids in bacteria and eukaryotes, and isoprenoids in archaea
Yosuke Koga (2012): In prokaryotic and eukaryotic cells, the (fatty acid) carbon chains are mainly linear but archaeal lipids are branched every fourth carbon, with a single methyl group linked to these carbon atoms. The unique structure of archaeal lipids and their stereospecificity was hypothesized to be responsible for the ability of these organisms to resist and thrive under extreme environmental conditions 16

C. de Carvalho ( 2018):The pathway for FA biosynthesis is highly conserved within the kingdoms of life, starting with the formation of malonyl-CoA by carboxylation of acetyl-CoA and further condensation of malonyl-CoA with acetyl-CoA with the release of CO2.  Studies on de novo synthesis of FA in Archae are rare. Archaeal membrane phospholipids are considered to incorporate isoprenoids instead of FA 15

The building blocks of isoprenoids ( used in archaea) are universal carbon five subunits called isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP) that are isomers. The biosynthetic pathway leading to the synthesis of IPP and DMAPP vary in different organisms.  To date, three distinct pathways are known. 17

How did the transition from the prebiotic synthesis of fatty acids in bacteria and eukaryotes, and isoprenoids in archaea occur? This is a huge step, a large gap, that is unexplained. 

Maheen Gull (2021): Glycerol is the structural backbone of lipid molecules (triacylglycerols). It is synthesized from sn-glycerol-3-phosphate in the presence of an enzyme called glycerol-3-phosphate phosphatase. In order to understand how life started, we need to understand the prebiotic origin of glycerol. One of the first questions for the origin/prebiotic synthesis of glycerol is the ‘site of origin’. For instance, the environments that can lead to the formation of glycerol rely on reduced carbon species (as glycerol is even more reduced in oxidation state than formaldehyde) and generally UV-rich sources for polymerization. This is in contrast to the formation of fatty acids, which has generally been considered as a product of hydrothermal systems (which are generally H2O and hydrocarbon-rich) or Fisher-Tropsch type reactions. Therefore the combination of such systems is questionable owing to the significant difference between these environments, such as pressure, temperature, and pH. The classical formose reaction has been reported to produce certain chemical derivatives of glycerol such as 2-hydroxymethyl glycerol, along with pentaerythritol. 11

The authors then cite several sources and conclude: The above-mentioned experiments under simulated astrophysical environments, i.e., very low temperatures (typically, <20 K), very low pressures (typically, <10−8 mbar), and high doses of ionizing radiation (typically, UV, extreme UV, or X-ray photons, high-energy electrons, or high-energy protons) plausibly show a universal process in space for the formation of glycerol. To this end, extraterrestrial and terrestrial sources may have both been sources of glycerol on the early Earth.

Prebiotic origin of glycerol and glycerol precusors
M.Fiore (2022): The prebiotic synthesis yields racemic glycerol phosphate mixtures, while biotic syntheses are catalyzed by specific enzymes, producing either sn-G1P ( bacteria) or sn-glycerol-3-phosphate (G3P) ( archaea). [url=https://www.liebertpub.com/doi/10.1089/ast.2021.0059#:~:text=4.-,Prebiotic Synthesis of Complete and Incomplete Phospholipids,complete lipids (CLs%2C cf.]39[/url]

What science papers can do, is outline the differences between the synthesis of G1P in bacteria, and G3P in archaea, but there is no detailed explanation of the prebiotic, to biotic synthesis ( and the mechanisms/forces that promoted that transition, and either why the divergent biosynthesis pathways in archaea and bacteria/eukaryotes emerged.  

The unsolved problem of symmetry breaking from prebiotic racemic mixtures, to homochiral phospholipids used in life
Emiliano Altamura (2020): In a series of papers published in 1848, Louis Pasteur argued that the crystals, composed of the same molecules, were bearing different symmetries. When combined in what is now called a racemic mixture, the different molecules cancelled each other’s ability to rotate the direction of uniformly polarized light. At the time, Pasteur probably ignored the fact that he was giving birth to one of the major questions of natural sciences: given that racemic mixtures are produced in any achiral environment, and that both mirror-imaged molecular forms, now called enantiomers, have, to the limits of detection, exactly identical energies and reactivity, how did the biological homochiral world emerge from the primitive inanimate and achiral environment? In other words, the big question is not the appearance of chiral molecules, but how the population symmetry of dissymmetric objects was broken, that is, the fact that dissymmetric objects of the same potential energy became strongly unequally populated. 23

Victor Sojo (2014): Homochirality, the exclusive prevalence of one chemical structure over its otherwise identical mirror image or enantiomer, the single-handedness of optically asymmetric chemical structures, is present and ubiquitous in all major groups of biological macromolecules. Terrestrial life’s preference for one isomer over its mirror image in D-sugars and L-amino acids has both fascinated and puzzled biochemists for over a century. A conclusive explanation for the evolutionary origin and maintenance of homochirality is still lacking. Although the phospholipid glycerol headgroups of archaea and bacteria are both exclusively homochiral, the stereochemistries between the two domains are opposite. The question, if any, lies in why nature went in one specific direction towards L-amino acids and D-sugars, rather than the opposite.  13

The author attributes this dual homochirality to "a simple evolutionary choice". The problem with this reasoning is that a) there was no evolution when that "choice" had to be made, and b) evolution cannot be anthropomorphized. It does not make any choices. Naturalistic/evolutionary explanations are entirely inadequate. 
Sojo continues: The carbonyl center of dihydroxyacetone phosphate (DHAP), from which both G1P and G3P are formed, is prochiral: hydrogenation from one side of the double bond produces G1P, while reacting from the opposite side gives G3P. At the atomic level, the amino acids of the active site of G3PDH face the pro-S hydrogen of NADH, whereas the G1PDH active site has been recently reported to exhibit a pro-R geometry. The idea of a nonstereospecific GP-synthase is difficult to reconcile with biochemical knowledge of the enzymes that catalyze these reactions.

Phospholipid biosynthesis is very different between bacteria and archaea,

The cell machinery is programmed to synthesize the glycerol moiety either right or left-handed. How was the gap between meteorites delivering glycerol organic compounds to the early earth, and the complex biosynthesis processes by complex enzyme machines overcome and bridged, to leap over it? Victor Sojo: Free-solution chemistry is not directly comparable to enzymatic catalysis.  The only satisfying answer seems to be that the machinery was designed from scratch. Life started fully developed, in the hand of the designer, who maybe knew that homo sapiens evolutionis scientificus was coming, and in order to leave him with interrogation points of his Darwinian theory, he made different lipid chiral directionality between archaea and bacteria.  

Emiliano Altamura (2020): Although the preparation of enantiopure phospholipid esters has been extensively reviewed during the past forty years, to the best of our knowledge, no large-scale synthesis of racemic phospholipids has ever been reported. Generally speaking, here we have concluded that racemic and scalemic ( enantiopure) lipids, in particular POPC ( phosphatidylcholine, an important phospholipid for biophysical experiments ), form stable membranes essentially, as well as homochiral lipids. 23

Why are phospholipid membranes homochiral?
The question of the biological significance of the phenomenon, this entrenched general biological sign of a living matter, is rarely discussed. 25  There must be a logic behind the fact that cell membranes are chiral. In mammalian cells, chiral recognition is a factor in mediating cell viability. 24 

John Harden (2009): Chiral lipids display piezoresponses while their racemic mixture does not. It demonstrates an important role played by lipid chirality in lyotropic phases and in membranes: it makes lamellar lyotropic phases piezoelectric. 26

Prebiotic origin of glycerol phosphates
Maheen Gull  (2021): Glycerol phosphates (GP) play a central role in modern biochemistry. These compounds are directly associated with crucial life processes, such as cellular respiration and cell structure. For a better understanding of the origin of early membranes, it is essential to understand the prebiotic syntheses of GP, which also are critical to the synthesis of phospholipids, an essential component of cell membranes in almost all organisms . GP links via a phosphate diester bond to form a ‘head group’ that is the polar/hydrophilic part of the phospholipid molecule.  Prebiotic syntheses of GP have been reported previously by using ammonium phosphates to phosphorylate glycerol with condensation agents at 85 °C, under simulated hydrothermal conditions and by using various minerals and clays as catalysts by employing various non-aqueous solvents, by using high energy phosphates such as amidophosphates, and by the formation of activated phosphate, e.g., imidazole phosphate, which then reacts with the organic compounds. In addition, the syntheses of GP from the meteoritic mineral schreibersite have been reported.

The above-mentioned methods have challenges such as the use of non-aqueous solvents that may not be prebiotically prominent. High energy conditions may degrade organic substrates and use of high energy phosphates, which are uncommon in the rock record.  

From prebiotic synthesis to the biotic synthesis of glycerol phosphates
Maheen Gull  (2021): In bacteria and eukaryotes, Glycerol kinase (GK) catalyzes the synthesis of G3P from glycerol. There are two biosynthetic pathways to obtain G3P from either DHAP or from glycerol.  In archaea, G1P is catalyzed by G1P dehydrogenase (G1PDH). There is only one pathway to obtain G1P from DHAP

Prebiotic origin of phospholipids
Juli Peretó (2004): The origin of cell membranes is a major unresolved issue. 47 Origin of life investigators have tried to find explanations of the prebiotic origin of the compounds required and ways to assemble them into amphiphile bilayers that could serve for the unguided self-assembly of the first cell membranes hosting the building blocks required to kick-start life. There have been several hypotheses for extraterrestrial sources, like carbonaceous chondrites, asteroids, etc. Most of these proposals are oversimplified, and large explanatory gaps exist. Cell membranes are generated from other membranes but not created from scratch. Usually, the hypotheses are from simple to complex. First, there were simple lipid droplets, then micelles, and last closed bilayer vesicles.  Fatty acids form usually micellar structures, while phospholipids, as bilayer structures, yield more stable vesicles than fatty acids 38

How could/would it be possible to go from simple chemistry compounds and their self-assembly to the complex biosynthesis pathways requiring multiple complex enzymes,  that diverge in the three domains of life? There is also the fact that there was no prebiotic selection process of the enantiomer handedness. If there was a cenancestor with a heterochiral membrane, how and why did a transition occur (racemic→scalemic→enantiopure) to divergent chiral form in bacteria and archaea?

Michele Fiore (2016): An implicit assumption behind this analysis is that prebiotically formed amphiphiles (“pre-Darwinian” amphiphiles, before proto-cellular replication set in), which assemble into membranes and close into semi-permeable boundaries of vesicular compartments (with a void volume inside), must be racemic (if chiral). 28

Sean F. Jordan (2018): Phospholipids are arguably too complex to have been formed via prebiotic chemical syntheses. [url=https://royalsocietypublishing.org/doi/10.1098/rsfs.2019.0067#:~:text=Isoprenoids are of interest as,in bacterial and eukaryotic membranes.]18[/url]

David W. Deamer (2010): Phospholipids spontaneously form bilayer vesicles having dimensions in the range of bacterial cells. Lipid bilayer vesicles are commonly referred to as liposomes, and such self-assembled membrane structures can be used as models of the earliest cell membranes. A variety of membranous structures can also be prepared from single-chain amphiphiles such as fatty acids. Such vesicles are plausible models for the formation of early cellular compartments. An important aspect of this argument is that the prebiotic availability of such amphiphiles has been established. Carbonaceous meteorites contain a rich mixture of organic compounds that were synthesized abiotically in the early solar system, and this mixture can be used as a guide to the kinds of organics likely to be available on the early Earth, either delivered during late accretion or synthesized at the Earth’s surface. 19

Drake Lee  (2018): The origin of fatty acids on the prebiotic Earth is important as they likely formed the encapsulating membranes of the first protocells. Carbon-rich meteorites (i.e., carbonaceous chondrites) such as Murchison and Tagish Lake are well known to contain these molecules, and their delivery to the early planet by intense early meteorite bombardments constitutes a key prebiotic source. We collect the fatty acid abundances measured in various carbonaceous chondrites from the literature and analyze them for patterns and correlations. Fatty acids in meteorites include straight-chain and branched-chain monocarboxylic and dicarboxylic acids up to 12 carbons in length—fatty acids with at least 8 carbons are required to form vesicles, and modern cell membranes employ lipids with ∼12–20 carbons.  Straight-chain monocarboxylic acids (SCMA) are the dominant fatty acids in meteorites, followed by branched-chain monocarboxylic acids (BCMA). Vesicles can be composed of a single fatty acid type as short as 8 carbons in length. Meteorites contain fatty acids 2–12 carbons in length. Therefore vesicles could indeed form directly out of meteorite-delivered fatty acids. [url=https://arxiv.org/pdf/1809.09779.pdf#:~:text=Fatty acids in meteorites include,with %E2%88%BC12%E2%80%9320 carbons.]22[/url]

Benoit E. PRIEUR (1995) Of all the questions pertaining to the origins of life, the prebiotic synthesis of fatty acids has given scientists the most difficulty. The chemistry is not easy, but we do know that all prebiotic synthesis would have to be simple, fast, and possible in vast quantities.  27

Prebiotic Synthesis of Complete and Incomplete Phospholipids
Michele Fiore (2016): The prebiotic synthesis of phospholipids can be divided into two steps:  the formation of incomplete lipids (IL), the critical step being the acylation of glycerol, and second, the phosphorylation of such into complete lipids (CLs). Both acylation of glycerol and phosphorylation fall under the category of condensation reactions, which require the elimination of one molecule of water. 28

Prebiotic phospholipid bond formation
Libretext: The fatty acids are attached to the glycerol at the 1 and 2 positions on glycerol through ester bonds. The third oxygen on glycerol is bonded to phosphoric acid through a phosphate ester bond (oxygen-phosphorus double bond oxygen). In addition, there is usually a complex amino alcohol also attached to the phosphate through a second phosphate ester bond. The phosphate group has a negatively charged oxygen and a positively charged nitrogen to make this group ionic. In addition, there are other oxygen of the ester groups, which make on whole end of the molecule strongly ionic and polar. 31

Sutter M (2015): Phospholipid ethers are complex molecules and their synthesis in the laboratory requires several steps, including protections and deprotections of the glycerol backbone and the polar head 40  Evidently, there were no such conditions existing on the early earth.

No prebiotic explanation for the origin of complete lipids (CLs)
Michele Fiore (2016):  One of the challenges in this field is to discover plausible reaction pathways that allow the synthesis of complete lipids (CLs) from simple polyols (glyceraldehyde or glycerol), long alkyl chains (primary alkanols or fatty acids), in the presence of a reactive phosphorous source. An important approach for establishing an evolvable chemical system is to supply a population of vesicles with amphiphilic components that insert into the membrane of existing vesicles, leading to vesicle growth and division, thus to the growth in population size and an evolution of “shape replicating” compartments (vesicles). To achieve this, the amphiphiles that are supplied should have a critical vesicle concentration (cvc) similar or somewhat higher than that of the amphiphiles composing the vesicles. Once inserted, the added amphiphiles, if chemically different from those in the vesicles, should eventually be transformed into “first generation” amphiphiles without diffusing out of the vesicles. Otherwise, they would form a separate set of de novo vesicles upon chemical transformation.

This is a major hurdle in the evolutionary transition from fatty acid vesicles to phospholipid vesicles, which requires esterification of fatty acids with, for example, phosphoglycerol. Fatty acids need 105-fold higher minimal concentrations to form vesicles than phospholipids, and the average residing time of fatty acids in membranes is much shorter than that of phospholipids. As a result, any chemical reaction involving fatty acids would take place outside the vesicles, thereby interrupting the evolution of the parent vesicles’ contents.

The transition from the prebiotic to biotic synthesis and formation of phospholipid cell membranes
Gáspár Jékely asks: Did the last common ancestor have a biological membrane? (2006)  The last common ancestor was associated with a hydrophobic layer with two hydrophilic sides (an inside and an outside) that had a full-fledged and asymmetric protein insertion and translocation machinery and served as a permeability barrier for protons and other small molecules. It is difficult to escape the conclusion that the last common ancestor had a closed biological membrane from which all cellular membranes evolved. The universal presence of two transmembrane proteins, the F0F1-ATPase and SecY seems to suggest that the universal ancestor was a membrane-bound cell 34

Kepa Ruiz-Mirazo (2013): The structure of most of lipids and surfactant compounds (e.g., phospholipids, glycolipids, cholesterol, etc.) is in general quite complex, and the probability that they were formed prebiotically seems rather low. It is considered very improbable that fatty acids, glycerol, and phosphate (i.e., the standard molecular components of a phospholipid) could have been present together in high enough concentrations on the primordial Earth.. In living organisms, cellular division occurs very regularly, after a growth phase, but this is a genetically controlled process, which relies on a complex membrane of diverse composition and, once more, on a suite of concerted macromolecular mechanisms in action. 36

The degradation problem
Michele Fiore (2016): Lipids are chemically and thermally relatively labile over geological timescales. Extracts from the remnants of extraterrestrial objects that entered the Earth’s atmosphere (meteorites), or from samples taken by a lander instrument (on planets, moons, asteroids, and comets) are expected to contain at best degradation products of lipids, viz. alkanes, long-chain alcohols, polyols, and carboxylic acids.

Three chemically distinct starting ingredients were prerequisites: (a) a source of long-chain “fatty” acids, aldehydes, or alcohols, (b) a polyol scaffold-like glycerol that can bear one or two lipophilic chains and (c) a source of phosphate such as inorganic orthophosphate like glycerophosphate, for the direct synthesis of Complete Lipids CLs.28

1. Steven A. Benner: Planetary Organic Chemistry and the Origins of Biomolecules 2010 Jul; 2
2. Geoffrey Zubay: Origins of Life on the Earth and in the Cosmos  2000
3. J Oró: The origin and early evolution of life on Earth 1990
4. Norio Kitadai: Origins of building blocks of life: A review  2017
5. Martin M Hanczyc:  Primordial membranes: more than simple container boundaries 2017
6. Carl Sagan: Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life 09 January 1992
7. Daniel P.Glavin: Chapter 3 - The Origin and Evolution of Organic Matter in Carbonaceous Chondrites and Links to Their Parent Bodies 2018
8. ScienceDaily: How life arose on Earth: Researchers brew up organics on ice September 18, 2012
10. David Deamer: The Role of Lipid Membranes in Life’s Origin 17 January 2017
11. Maheen Gull: The Role of Glycerol and Its Derivatives in the Biochemistry of Living Organisms, and Their Prebiotic Origin and Significance in the Evolution of Life 10 January 2021
12. Lena Vincent: The Prebiotic Kitchen: A Guide to Composing Prebiotic Soup Recipes to Test Origins of Life Hypotheses 11 November 2021
13. Victor Sojo: On the Biogenic Origins of Homochirality 27 November 2014
14. Jonathan Lombard: The early evolution of lipid membranes and the three domains of life  2012 Jun 11
15. Carla C. C. R. de Carvalho: The Various Roles of Fatty Acids 2018 Oct; 23
16. Yosuke Koga: Thermal adaptation of the archaeal and bacterial lipid membranes 2012 Aug 15.
17. Samta Jain: Biosynthesis of archaeal membrane ether lipids 2014 Nov 26
18. Sean F. Jordan: [url=https://royalsocietypublishing.org/doi/10.1098/rsfs.2019.0067#:~:text=Isoprenoids are of interest as,in bacterial and eukaryotic membranes.]Isoprenoids enhance the stability of fatty acid membranes at the emergence of life potentially leading to an early lipid divide[/url] 18 October 2019
19. David W. Deamer: Membrane Self-Assembly Processes: Steps Toward the First Cellular Life 13 October 2010
20. Eugene V. Koonin  On the origin of genomes and cells within inorganic compartments 2005 Dec; 21
22. Drake Lee: [url=https://arxiv.org/pdf/1809.09779.pdf#:~:text=Fatty acids in meteorites include,with %E2%88%BC12%E2%80%9320 carbons.]Meteoritic Abundances of Fatty Acids and Potential Reaction Pathways in Planetesimals[/url] Sept. 24, 2018
23. Emiliano Altamura: Racemic Phospholipids for Origin of Life Studies 3 July 2020
24. Kohei Sato: Chiral Recognition of Lipid Bilayer Membranes by Supramolecular Assemblies of Peptide Amphiphiles May 31, 2019
25. Ekaterina V. Malyshko: Chiral Dualism as a Unifying Principle in Molecular Biophysics 8 February 2021
26. John Harden: Chirality of lipids makes fluid lamellar phases piezoelectric  2009 Jan 7.
27. Benoit E. PRIEUR: ORIGIN of FATTY ACIDS  1995
28. Michele Fiore: Prebiotic Lipidic Amphiphiles and Condensing Agents on the Early Earth 28 March 2016
29. Libretext: Lipids
30. Libretexts: Components and Structure - Membrane Fluidity
31. Libretext: [url=https://chem.libretexts.org/Bookshelves/Biological_Chemistry/Supplemental_Modules_(Biological_Chemistry)/Lipids/Glycerides/Phosphoglycerides_or_Phospholipids#:~:text=The third oxygen on glycerol,a second phosphate ester bond.]Phosphoglycerides or Phospholipids[/url]
32. Arnold J. M. Driessen: Biosynthesis of archaeal membrane ether lipids  26 November 2014
33. Stephanie Ballweg: Control of membrane fluidity: the OLE pathway in focus October 27, 2016
34. Gáspár Jékely: Did the last common ancestor have a biological membrane? 2006 Nov 27
35. Daniel Segré: The Lipid World February 2001
36. Kepa Ruiz-Mirazo: Prebiotic Systems Chemistry: New Perspectives for the Origins of Life October 31, 2013
37. David Deamer: The Role of Lipid Membranes in Life’s Origin   17 January 2017
38. Augustin Lopez: Chemical Analysis of Lipid Boundaries after Consecutive Growth and Division of Supported Giant Vesicles 2020 Nov 20
39. Michele Fiore: [url=https://www.liebertpub.com/doi/10.1089/ast.2021.0059#:~:text=4.-,Prebiotic Synthesis of Complete and Incomplete Phospholipids,complete lipids (CLs%2C cf.]Synthesis of Phospholipids Under Plausible Prebiotic Conditions and Analogies with Phospholipid Biochemistry for Origin of Life Studies[/url] 10 May 2022
40. Marc Sutter: Glycerol Ether Synthesis: A Bench Test for Green Chemistry Concepts and Technologies July 21, 2015
41. Dr. Peter Reilly: Biosynthesis of Fatty Acids  2021
42. Maheen Gull: Catalytic Prebiotic Formation of Glycerol Phosphate Esters and an Estimation of Their Steady State Abundance under Plausible Early Earth Conditions 17 November 2021
43. Robert Ernst: Homeoviscous Adaptation and the Regulation of Membrane Lipids 4 December 2016
44. Natalia Soledad Paulucci: Membrane Homeoviscous Adaptation in Sinorhizobium Submitted to a Stressful Thermal Cycle Contributes to the Maintenance of the Symbiotic Plant–Bacteria Interaction 17 December 2021
45. Doris Berchtold: TOR complex 2 regulates plasma membrane homeostasis Mai 2012
46. Robert Shapiro: A simpler origin for life 2007 Jun;2
47. Juli Peretó: Ancestral lipid biosynthesis and early membrane evolution 2004 Sep;29
48. Eugene V. Koonin: Inventing the dynamo machine: the evolution of the F-type and V-type ATPases November 2007




What came first: Lipid membranes, or membrane proteins?
Eugene V. Koonin (2009): A topologically closed membrane is a ubiquitous feature of all cellular life forms. This membrane is not a simple lipid bilayer enclosing the innards of the cell: far from that, even in the simplest cells, the membrane is a biological device of a staggering complexity that carries diverse protein complexes mediating energy-dependent – and tightly regulated - import and export of metabolites and polymers. Despite the growing understanding of the structural organization of membranes and molecular mechanisms of many membrane proteins, the origin(s) of biological membranes remain obscure. 7

Armen Y. Mulkidjanian (2010) The origins of membrane proteins are inextricably coupled with the origin of lipid membranes. Indeed, membrane proteins, which contain hydrophobic stretches and are generally insoluble in water, could not have evolved in the absence of functional membranes, while purely lipid membranes would be impenetrable and hence useless without membrane proteins. The origins of biological membranes – as complex cellular devices that control the energetics of the cell and its interactions with the surrounding world – remain obscure 8

Eugene V. Koonin: The origin of the cellular membrane itself seems to involve a catch-22: for a membrane to function in a cell, it must be endowed with at least a minimal repertoire of transport systems but it is unclear how such systems could evolve in the absence of a membrane. 6

The challenge to start harvesting energy
Geoffrey Zubay (2000):  Metabolism depends on factors that are external to the organism. The living system must extract nutrients from the environment and convert them to a biochemically useful form. In the next phase of the metabolism, which is internal, small molecules are synthesized and degraded. 19

Jeremy England (2020): EVERY LIFE IS ON FIRE How Thermodynamics Explains the Origins of Living Things: A spring has first to be brought to a compressed state, that is ready to burst apart, forcefully, when properly triggered. When glass and dishes are thrown to the ground, the stored energy is released, but they get smashed, broken, or damaged. Accordingly, people can eat sugar, but not dynamite; plants love sunlight,  but not intense gamma rays. Life needs access to energy, but it has to absorb it in specific ways that are conducive to activating “healthy” motions while avoiding “unhealthy” ones. To get a little bit more technical, it helps to remember that living things are in highly specialized, exceptionally rare configurations of their constituent parts that would not easily be discovered by a random and unbiased search of the space of their possible arrangements. 17

ADDY PROSS (2012) Organized complexity and one of the most fundamental laws of the universe—the Second Law of Thermodynamics—are inherently adversarial. Nature prefers chaos to order, so disorganization is the natural order. Within living systems, however, the highly organized state that is absolutely essential for viable biological function is somehow maintained with remarkable precision. : The living cell is able to maintain its structural integrity and its organization through the continual utilization of energy, which is in fact part of the cell’s modus operandi. . So there is no thermodynamic contradiction in life’s organized high-energy state, just as there is no contradiction in a car being able to drive uphill in opposition to the Earth’s gravitational pull, or a refrigerator in maintaining a cool interior despite the constant flow of heat into that interior from the warmer exterior. Both the car driving uphill and the refrigerator with its cold interior can maintain their energetically unstable state through the continual utilization of energy. In the car’s case the burning of gasoline in the car’s engine is the energy source, while in the case of the refrigerator, the energy source is the electricity supply that operates the refrigerator’s compressor. In an analogous manner, energetically speaking, the body can maintain its highly organized state through the continual utilization of energy from some external source—the chemical energy inherent within the foods we eat, or, in the case of plants, the solar energy that is captured by the chlorophyll pigment found in all plants. But how the initial organization associated with the simplest living system came about originally is a much tougher question. 15




The Hot Spring Hypothesis for an Origin of Life
Bruce Damer and David Deamer

Temperature and Stability: Hot springs are characterized by high temperatures, which can be detrimental to the stability of complex organic molecules like RNA. RNA is prone to degradation at high temperatures, making it challenging for the necessary biomolecules to persist and accumulate in such environments.

Lack of Concentration: Hot springs generally have dilute solutions due to high water flow, which can result in low concentrations of crucial organic molecules. Prebiotic chemistry requires a sufficient concentration of building blocks, such as amino acids or nucleotides, for the emergence of life-like processes. The low concentration of these molecules in hot springs may hinder the formation of complex organic structures.

Harsh Chemical Conditions: Hot springs often contain high levels of minerals and metal ions, which can have inhibitory or destructive effects on prebiotic chemistry. These chemical conditions may interfere with the formation and stability of key biomolecules, potentially hindering the emergence of life.

Narrow Environmental Range: Hot springs represent a specific type of geothermal environment, characterized by high temperatures, mineral-rich water, and unique physical conditions. While these conditions may be suitable for certain life forms, they may not be representative of the broader range of environments on early Earth where life could have originated. Critics argue that the Hot Spring Hypothesis does not adequately address the diversity of potential environments involved in the origin of life.

Lack of Experimental Evidence: Currently, there is a lack of direct experimental evidence supporting the specific mechanisms proposed by the Hot Spring Hypothesis. While the hypothesis is based on logical extrapolations from known properties of hot springs, more experimental work and evidence are needed to validate its claims.

Hot springs, with their high temperatures and unique chemical conditions, present obstacles to the stability of complex organic molecules like RNA. RNA is particularly susceptible to degradation at elevated temperatures, making it difficult for the necessary biomolecules to persist and accumulate in hot spring environments. Additionally, the dilute solutions found in hot springs due to high water flow can result in low concentrations of crucial organic molecules. The emergence of life-like processes requires sufficient concentrations of building blocks like amino acids or nucleotides, which may be hindered in such environments. Furthermore, hot springs often contain high levels of minerals and metal ions, which can have inhibitory or destructive effects on prebiotic chemistry. These harsh chemical conditions may interfere with the formation and stability of key biomolecules, further challenging the origin of life in hot springs. Another aspect to consider is the narrow environmental range of hot springs. While these geothermal environments may provide suitable conditions for certain life forms, they may not represent the diversity of potential environments on early Earth where life could have emerged. Critics argue that the Hot Spring Hypothesis, which suggests that life originated in hot springs, may not adequately account for the broad range of environments involved in the origin of life. The Hot Spring Hypothesis lacks direct experimental evidence to support its specific mechanisms. While the hypothesis is based on logical extrapolations from known properties of hot springs, further experimental work and evidence are necessary to validate its claims. This highlights the ongoing need for research and investigation into the role of hot springs in the origin of life.



Sponsored content

Back to top  Message [Page 1 of 1]

Permissions in this forum:
You cannot reply to topics in this forum