Is photosynthesis irreducibly complex ?
There is a common claim that that irreducible complexity in biology has been refuted. But has it? This video addresses this issue.
In photosynthesis , 26 protein complexes and enzymes are required to go through the light and light independent reactions, a chemical process that transforms sunlight into chemical energy, to get glucose as end product , a metabolic intermediate for cell respiration. A good part of the protein complexes are uniquely used in photosynthesis. The pathway must go all the way through, and all steps are required, otherwise glucose is not produced. Also, in the oxygen evolving complex, which splits water into electrons, protons, and CO2, if the light-induced electron transfer reactions do not go all the five steps through, no oxygen, no protons and electrons are produced, no advanced life would be possible on earth. So, photosynthesis is a interdependent system, that could not have evolved, since all parts had to be in place right from the beginning. It contains many interdependent systems composed of parts that would be useless without the presence of all the other necessary parts. In these systems, nothing works until all the necessary components are present and working. So how could someont rationally say, the individual parts, proteins and enzymes, co-factors and assembly proteins not present in the final assemblage, all happened by a series of natural events that we can call ad hoc mistake "formed in one particular moment without ability to consider any application." , to then somehow interlink in a meaningful way, to form electron transport chains, proton gradients to " feed " ATP synthase nano motors to produce ATP , and so on ? Such independent structures would have not aided survival. Consider the light harvesting complex, and the electron transport chain, that did not exist at exactly the same moment--would they ever "get together" since they would neither have any correlation to each other nor help survival separately? Repair of PSII via turnover of the damaged protein subunits is a complex process involving highly regulated reversible phosphorylation of several PSII core subunits. So it seems that photosynthesis falsifies the theory of evolution, where all small steps need to provide a survival advantage.
Chloroplast & Chlorophyll
A modern leaf with 70 million cells will contain about five billion chloroplasts, each containing about 600 million molecules of chlorophyll.
Approximately 250 to 300 of them transfer the absorbed light energy through neighbouring pigments to the “special pair” chlorophylls in a reaction center. These special pair chlorophylls in photosystems I and II are the primary electron donors that drive the conversion of light into chemical energy.
Since the pyrrole ring is responsible for the colour of Chlorophylls, its also called a chromophore. The basic structure is a ring made of four pyrroles, a tetrapyrrole, which is also named porphyrin. Its large inner surface area has a high cross-section suited for photon capture. Chlorophylls are excellent light absorbers. 27s
A modern leaf with 70 million cells will contain about five billion chloroplasts, each containing about 600 million molecules of chlorophyll. Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight.
The tetrapyrrole system shows a high absorptivity at both the long- and short-wavelength ends of the visible spectrum of light. The middle of the light spectrum is not absorbed but reflected, which is the reason why leaves are usually green. 21s
How exactly do Chlorophyll pigments “capture” the energy of light? In the picture, we see two photosystems, which are surrounded by light-harvesting antennas. There, Chlorophylls are embedded, capturing photons. 17s
The photosynthesis pathway starts with light absorption which excites the chlorophyll molecule. Then, the energy is passed from molecule to molecule until it reaches the reaction-center complex. Here, an excited electron from the special pair of chlorophyll a molecules are transferred to the primary electron acceptor. 26s
When chlorophyll absorbs a photon, an electron excitation in its ring structure occurs, which moves electrons from the ground state into a higher excited state in the atoms. A sequence of alternating double and single bonds in rings, which form a system of conjugated bonds, is responsible for light absorption. 26s
A photon can be envisioned as a very fast-moving packet of energy. When it strikes a molecule, its energy is either lost as heat or absorbed by the electrons of the molecule, boosting those electrons into higher energy levels. Whether or not the photon’s energy is absorbed depends on how much energy it carries (defined by its wavelength) and on the chemical nature of the molecule it hits. Electrons occupy discrete energy levels in their orbits around atomic nuclei. To boost an electron into a different energy level requires just the right amount of energy, just as reaching the next rung on a ladder requires you to raise your foot just the right distance. A specific atom can, therefore, absorb only certain photons of light—namely, those that correspond to the atom’s available electron energy levels. 68s
Magnesium is present in the center of the ring as the central atom. If other metals instead of magnesium are used, they will competitively quench and extinguish the chlorophyll's excited state and return to the ground state. Consequently very little if any energy transfer would occur. This means that insufficient energy would reach the reaction center and the process would not continue. Magnesium chlorophyll has a unique property which is that the absorption and emission spectra overlap exceptionally well.
That means that energy transfer to nearby molecules by the Forster (resonance) mechanism is very favourable. Magnesium chlorophyll has almost the best possible overlap of absorption and emission spectra of any molecules. All of this illustrates that photosynthesis is finely tuned, and small changes can have dramatic effects. Copper and zinc form complexes with chlorophyll, but with different affinities and functions. 80s
How could natural selection fix the right information in the genome to instruct the import, purification, and precise insertion of the right central atom with the required functional properties and how to insert in in the right geometric position to bear function? Each change and trial would require the change of a whole system of metal recognition and import channels in the cell membrane, finely adjusted for the right metal. 33s
In fact, on the archaean ocean, a wide variety of trace minerals would have been available, as above mentioned science paper reports. 11s
For example, the import channels for magnesium are illustrated above and radically different than import channels for Copper. 8s
This demonstrates that when one tiny item is changed, a much larger change on systems level has to occur. Metal metabolism, as occurs with many cellular processes, is interconnected which raises strong doubts if that are not hurdles far beyond what evolution is capable of overcoming to produce new traits and functions. 26s
The chlorophyll tail is a phytol hydrocarbon chain, which is attached to the pyrrole. It is not involved in light absorption but it has the essential function to anchor chlorophylls in the light-harvesting complex and provides chlorophylls with the right orientation. Without the tail, chlorophylls would have no way to anchor in the light-harvesting complex. But there is a surprising mutual benefit. Light-harvesting complexes in plants do contain not only Chlorophyll type a, but also Chlorophyll b, and carotenoids. Chlorophyll b helps and is actually even essential for the assembly of the light harvesting complex 40s
Remarkably, Chlorophyll b's, which are produced by the Chlorophyll cycle, are required for the assembly of the Light harvesting complex. The major peripheral Light-harvesting complexes contain nearly equal numbers of Chlorophyll a and Chlorophyll b, which are held in highly specific positions. The complex is assembled via a defined pathway and the final product is stabilized by Chlorophyll b which are essential for that process. There would be no use of light harvesting antenna complexes without chlorophylls. But there would be no use for Chlorophylls either, without the right arrangement in antenna complexes! 48s
How can evolution by gene mutations and natural selection explain its origin, if foreknowledge is required for the final function? 8s
In the photosynthesis pathway, more than 24 protein complexes which compose the system must first be synthesized and assembled in the right order and then interconnected to form a functional whole, able to start operating.
Thylakoid membranes are like the factory floor. There the photosynthetic electron transport is carried out using some of the most sophisticated macromolecular multisubunit complexes in nature. 33s
Recent years have seen major breakthroughs in elucidating the ultrastructure of all core constituents of these complexes, like photosystem II. They are composed of dozens of protein subunits as well as hundreds of organic and inorganic co-factors, most of which are embedded in the lipid bilayer of thylakoid membranes. 25s
Photosystem II is vulnerable to oxidative damage. When this occurs, it undergoes an impressive repair cycle in a multi-step process. Specifically orchestrated degradation of photodamaged subunits are crucial steps in the repair cycle to maintain photosynthesis activity. How could such ultrasophisticated and essential repair and recycling have evolved in a gradual stepwise fashion, if, not implemented right from the start, the protein complex would soon be burned by reactive oxygen species as a response to high light and high temperature and cease its function? 50s
Such sophisticated, inbuilt protection and repair mechanisms are truly awe-inspiring, surprising, and point clearly to the requirement of designed and foreplanned implementation and creation. The biogenesis process includes the highly-ordered, step-wise assembly of proteins, lipids, pigments like chlorophyll (Chl), and carotenoids, quinones, and metal ions which to a large extent is mediated by dedicated assembly factors assisting specific steps. 40s
Remarkably, the assembly takes place in specialized membranous compartments which are distinct from functional thylakoid membranes but involved in the synthesis and assembly of at least some photosynthetic components, especially photosystem PSII. The Illustrations show: (A) a Synechocystis cell with a biogenesis center and other relevant compartments; (B) a higher magnification view of a biogenesis center formed by the central thylakoid center and (C) a Chlamydomonas cell with intracellular compartments. 45s
The transfer of an enzymatic pathway and finished products from one compartment to another poses severe problems: the enzymes of the pathway acquire their targeting signals for the new compartment individually, not together, and at the same time. Until the whole pathway is established in the new compartment, newly routed individual enzymes are useless, and their genes will be lost through mutation. 34s
This all is evidence that the synchronization and requirement of massive new information and precise regulation orchestrating such processes is far best explained by intelligent design.
We will now move on to give a closer look into the biosynthesis of Chlorophyll, which impressive on its own merit. 13s
We will now move on to give a closer look into the biosynthesis of Chlorophyll, which impressive on its own merit. The production of manmade solar panels requires seven highly specific steps as outlined earlier in this video. We can draw a parallel to Chlorophyll biosynthesis, which in a similar fashion, requires seventeen consecutive manufacturing steps. Imagine a production line in a factory. Many robots there are lined up, and raw materials are fed into the production line. The materials arrive at Robot one. It processes the first step. Then, when ready, the product moves on and is handed over to the next Robot. Next processing step. And that procedure repeats 17 times. Instead of robots, each step is performed by specific enzymes, which catalize the metabolic reactions. 58s
In the end, there is a fully formed chlorophyll molecule. It is part of the larger system, namely the complete photosynthesis pathway. Chlorophyll by its own has no use unless mounted at the right place in the light-harvesting complex, in the right order. 20s
They are only functional when they are inserted in the light-harvesting complex, where 200 to 300 work in a joint venture, with the right distances from each other, in the right functional order, to catch photons and direct their excitation energy by Förster resonance energy transfer to the reaction center in Photosystems one and two.
Foreplanning is absolutely essential. Individually, chlorophylls have no function.
Chlorophylls and the light harvesting complex form a functional unity. But the genes that produce the proteins of chlorophyll metabolism, and synthesis of the light-harvesting complex, are different and separated. 15s
Remarkably, no Light harvesting binding proteins accumulate in the absence of pigment synthesis and adjustment of the photosynthetic subunits requires a coordinated biosynthesis of apoproteins and Chlorophyll chromophores. 18s
Chlorophylls a and b are both required for stabilization of the apoproteins and assembly of the majority of antenna complexes in higher plants. 11s
So there is a clear interdependence. This is a major problem for evolution. 7s
Why and how would evolution produce separately several proteins exclusively for chlorophyll synthesis, before the existence of light-harvesting complexes where they are embedded and bound to, and the regulatory instructions orchestrating the assembly of the whole complex? 21s
The binding site is precisely engineered and orchestrated, and the entire assembly of the complex depends on Chlorophylls. But more problems await for who advocates that evolution is a plausible explanation. The last eight steps of chlorophyll biosynthesis are used by specific enzymes uniquely in this pathway. 25s
The common cop-out that some parts could have been co-opted from somewhere else does not apply to these enzymes since they have not known multiple functions. So the whole pathway would have had to emerge from scratch.
This is a key point of the argument in this video:21s
What good would there be for natural selection to select and produce enzymes, used in this complex manufacturing process, without all the other enzymes in place, and the whole process coordinated to get a useful end product? 18ss
What good would there be, if the chlorophyll pathway would go only partially the way through, let's say, up to the 12th step?? 11s
A non-functional intermediate molecule would be the product, not performing anything helping the organism to survive. 10s
Worse that that: It would eventually produce an intermediate product, which in the process, as waste product would produce reactive oxygen species, which would harm the cell. 14s
What good would there be, if the chlorophyll pathway would go all the way through up to the 17th step? Chlorophyll would be produced, BUT:13s
What good for survival would there be for chlorophyll on its own, if not fully and correctly embedded in the photosynthesis process? none. 11s
What good would there be for photosynthesis without chlorophyll in place, capturing light, and transmitting it to the photosystem? none, since capturing light is essential for the whole process. 16s
‘Why would evolution produce a series of enzymes that only generate useless intermediates until all of the enzymes needed for the end product have evolved?’ 12s
Blankenship notes in Molecular mechanisms of photosynthesis: It is not conceivable that highly complex molecules such as chlorophylls were synthesized by prebiotic chemistry, given their very specific functional groups and multiple chiral centers. 19s
The thing is, there's no driver for any of the pieces to evolve individually because single parts confer no advantage in and of themselves. The necessity for the parts of the system to be in place all at once is simply evidence of creation. 21s
Due to the remarkable reactivity of all tetrapyrroles, there is in living organisms a substantial danger that uncontrolled chemical reactions may occur and ultimately lead to damage of cellular and subcellular structures. All living organisms thus need strategies to neutralize the potentially harmful tetrapyrrole compounds. 27s
In most cases, this task is achieved by tightly controlling their actual concentrations, in order for the level of free tetrapyrroles within a cell being kept to a minimum. 14s
Chlorophyll triplets are harmful excited states readily reacting with molecular oxygen to yield the reactive oxygen species (ROS) singlet oxygen. 14s
Carotenoids have an essential photoprotective role in photosynthetic membranes by preventing photooxidative damage through quenching of chlorophyll singlets and triplets. They do it with an amazing efficiency of 94−97%. 19s
When missing, the result is high level of photodamage in high light and/or low temperature. 8s
In addition, tetrapyrrole synthesis and degradation are carefully adjusted to the cellular requirements, reflecting the different needs under varying environmental conditions. 14s
During the assembly of the photosynthetic apparatus, chlorophylls and the nuclear-encoded and plastid-encoded chlorophyll-binding proteins must interact in a highly coordinated manner. 15s
This is an all or nothing business. The evidence points to the requirement of preprogramming to coordinate the strategies of protection from day one. Programming is always tracked back to intelligent action. 16s
Let's have a look at how science papers answer this question: 7s
Organisms generate an enormous number of metabolites; however, the mechanisms by which a new metabolic pathway is acquired are unknown. This is a monumental admission, since metabolic pathways are used and required in basically all life forms. 21s
Central to the topic is the Granick hypothesis from 1965, which posits that the evolution of the chlorophyll biosynthetic pathway followed the sequential inventions of new enzymes to generate more stable products. 17s
So basically, all which is proposed, is a baseless assertion which goes back to 1965 !! There are no details, no scientific evidence that it can occur - nothing !! 14ss
"recruitment of genes and the evolution of orphan genes have all been suggested to contribute.". This is a blank admittance that there is no hard, compelling de facto evidence. None. Nada. Njet. Only guesswork, and baseless suggestions. 19s
This video has demonstrated why there is no conceivable way to get a functional metabolic pathway with several enzymes lined up by happenstance, producing purposeful products without intelligent guidance. Enzymes, in order to become functional, must be specified in a precise manner to fold into complex 3D forms which need to be complementary with the substrates they process and act upon. This extremely remotely possible, if not impossible, unless the end goal, the " big picture" is known. Foreknowledge of the purpose is required, and what the end product will be. " Know-how" is required how to set up each enzyme, what specific synthesis step it has to perform, what its product is, which next enzyme is required to perform the next manufacturing step and so on.
There are very good reasons to be skeptic that genes would independently and blindly mutate to produce supercomplexes as seen in this video, that only bear function with other molecular machines working in a joint venture, these also supposedly products of genetic mutations, which by their own would bear no function either. On top of that, other genetic information has to orchestrate its assembly into functional working machines and all this from scratch and build in control, error detection, and repair mechanisms. I have not enough faith to believe, evolution and long periods of time have such superpowers. A blind brainless watchmaker isn't able to make a watch.
In this video, we have only scratched on the surface of photosynthesis. Much more can and should be said. That will hopefully be the case in the forthcoming videos. If you enjoyed, please subscribe to my channel, share the video, recommend, comment, and if you like, a contribution at patreon is appreciated.
Investigating the bifunctionality of cyclizing and “classical” 5-aminolevulinate synthases
Evolutionary Aspects and Regulation of Tetrapyrrole Biosynthesis in Cyanobacteria under Aerobic and Anaerobic Environments
V-shaped structure of glutamyl-tRNA reductase, the first enzyme of tRNA-dependent tetrapyrrole biosynthesis
Prokaryotic Heme Biosynthesis: Multiple Pathways to a Common Essential Product
Evolutionary Relationship between Initial Enzymes of Tetrapyrrole Biosynthesis
Identification of the chlE gene encoding oxygen-independent Mgprotoporphyrin IX monomethyl ester cyclase in cyanobacteria
Distribution and Origin of Oxygen-Dependent and Oxygen-Independent Forms of Mg-Protoporphyrin Monomethylester Cyclase among Phototrophic Proteobacteria
Evolution of a new chlorophyll metabolic pathway driven by the dynamic changes in enzyme promiscuous activity
The catalytic subunit of magnesium-protoporphyrin IX monomethyl ester cyclase forms a chloroplast complex to regulate chlorophyll biosynthesis in rice
Conserved Chloroplast Open-reading Frame ycf54 Is Required for Activity of the Magnesium Protoporphyrin Monomethylester Oxidative Cyclase in Synechocystis PCC 6803
Structural insights into the catalytic mechanism of Synechocystis magnesium protoporphyrin IX O-methyltransferase (ChlM).
Department of Molecular Biology and Biotechnology
Home > Molecular Biology and Biotechnology > People > Neil Hunter
Light Regulates Transcription of Chlorophyll Biosynthetic Genes During Chloroplast Biogenesis
Circadian and Plastid Signaling Pathways Are Integrated to Ensure Correct Expression of the CBF and COR Genes during Photoperiodic Growth1
Rapid C8-vinyl reduction of divinyl-chlorophyllide a by BciA from Rhodobacter capsulatus
X-ray crystal structure of the light-independent protochlorophyllide reductase
Evolution of light-independent protochlorophyllide oxidoreductase
Siroheme An essential component for life on earth
Organization of energy transfer networks in photosynthesis
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