Where did Glucose come from in a prebiotic world ?https://reasonandscience.catsboard.com/t2061p200-my-articles#7220
Although the usual example of a primordial fermentation is that of glucose, it is unlikely that large quantities of this sugar were available in the primitive environment because of its instability.
The ultimate origin of Glucose - sugars is a huge problem for those who believe in life from non-life without requiring a creator. In order to provide credible explanations of how life emerged, a crucial question must be answered : Where did Glucose come from in a prebiotic earth ? The source of glucose and other sugars used in metabolic processes would have to lie in an energy-collecting process. Without some means to create such sugar, limitations of food supply for metabolic processes would make the origin of life probably impossible.
Abiogenesis is understood enough to conclude, that the probabilities are too small, that life could have emerged naturally, without a guiding intelligence. A main unknown issue about the origin of life is to identify the first energy capture and carbon fixation mechanism used by the primitive organisms that populated the young biosphere. A prebiotic system should have also been able to implement the core reactions involved in central metabolism abiotically and nonenzymatically. One of them, the reverse TCA cycle is often proposed as the leading candidate to be the first carbon fixation mechanism. Sugars are versatile molecules, belonging to a general class of compounds known as carbohydrates, which serve a structural role as well as providing energy for the cell. Science today shifts its hope to find the solution of the riddle to hydrothermal vents because they are populated by chemoautotrophic bacterias, which use this alternative mechanism for Carbon fixation, namely the reverse Citric Acid Cycle, or tricarboxylic Cycle (TCA). The TCA is the central hub from which all basic building blocks for life are derived, by all three domains of life. So the origin of the TCA is a central OOL problem. The enzymes used in the cycle are:
1, malate dehydrogenase ( FDH )
2, fumarate hydratase (fumarase)
3, fumarate reductase
4, succinyl-CoA synthetase
5, 2-oxoglutarate:ferredoxin oxidoreductase
6, isocitrate dehydrogenase
7, aconitate hydratase (aconitase)
8, ATP citrate lyase
9, pyruvate:ferredoxin oxidoreductase Fdred, reduced ferredoxin.
Lets give a closer look just at the first enzyme.
In anaerobic organisms, FDH is an NAD+-independent enzyme containing a complex list of metal centers sensitive to oxygen, including tungsten (W), molybdenum (Mo), non-haem iron and molybdopterin guanine dinucleotide (MGD) cofactors.
These trace minerals and metals must be detected and be available in the surrounding of the place where life supposedly began. In modern cells, these metals are imported by extremely complex membrane transport channel proteins. Remember, in some of the life-essential proteins, the metal co-factors require the three elements: Iron, sulfur, and molybdenum. So these three have to be imported into the cell. Each one of the minerals has their own specific import channel proteins. Let's start with Iron. Iron is not available in a useful form for the cell. So before the import can begin, Iron has to be chelated and transformed into useful form. That occurs by an amazingly complex nano-factory called non-ribosomal peptide synthetase, which works like in factory assembly lines, transforming iron into so-called siderophores.
These siderophores are then detected by membrane channel proteins, bound and imported, using energy that is supplied by adenosine triphosphate. In the case of molybdenum, there is an extremely high affinity, and just a few, less than half a dozen amino acid residues at the right place in the protein recognize and bind the trace metal. If these residues are not the correct ones amongst twenty used in life, no deal, the metal is not recognized.
The same import process has to occur with iron, sulfur, and molybdenum. In the case of molybdenum, the metal has to be stored, once imported into the cell, to be available whenever needed. A storage protein has a special cage to store the metal, and special molecular needles are literally ejecting or shooting the metal into the cage to be stored there and at disposal when needed.
Once other signaling networks detect the need of the cell to synthesize a protein using metal clusters, the whole machinery is put to work and a whole orchestration to produce a metal cluster containing protein begins.
The metal clusters require a very complex assembly process. In the procedure, helper proteins are required, called chaperones, which conduct the metals to the assembly site, and help in the scaffolding and assembly. This is a multistep process, requiring various enzymes, this is a literal assembly line doing the process using various finely tuned molecular machines. Once the metal cluster is ready, it must be inserted into the protein through other helper proteins which know how exactly the cluster has to be inserted, and how to be bound to the nearby polypeptide chains of the apoprotein complex.
Of course, this is a simplified explanation, but it gives a grasp of the complexity of the whole process. Thousands of metal clusters containing proteins are required to kick-start the life-essential processes. Transcription of DNA, translation, etc.
And now consider, that some proteins do not require just one metal cluster, but various, often aligned in a very specific order to permit electron transport chains performing their duty.
And now consider, that all this had to emerge without evolution. Either by lucky accidents or design.
What mechanism explains the feat better?
Check out more info on molybden enzymes at my library, reasonandscience. The topic, search: Proteins with molybdenum clusters, essential for life
at the section: Origin of life.