Biomolecules carbon sources

Table 16.3 compiles the use of potato starch as a carbon source for the production of different biomolecules such as enzymes and organic acids. 

The gases usually postulated to have been present in the atmosphere of the early Earth include NH, H S, GO, GO, GH, N, H, and (in both liquid and vapor forms) H O. However, there is no universal agreement on the relative amounts of these components, from which biomolecules ultimately arose. Many of the earlier theories of the origin of life postulated GH as the carbon source, but more recent studies have shown that appreciable amounts of GO must have existed in the atmosphere at least 3.8 billion (3.8 x 10 ) years ago. 

The glyoxylate cycle also occurs in bacteria. This point is far from surprising because many types of bacteria can live on very limited carbon sources. They have metabolic pathways that can produce all the biomolecules they need from quite simple molecules. The glyoxylate cycle is one example of how bacteria manage this feat. 

In the years since Miller s experiment, ideas about the chemistry of life s origin have become more precise as a consequence of much experimentation and of exploration in outer space. We now know that the earth s primary atmosphere was formed mainly by degassing the molten interior rather than by accretion from the solar nebula. It seems likely that the main carbon sources in the earth s early atmosphere were CO2 and CO, not methane as assumed by Miller, and that nitrogen was present mainly as N2 rather than as ammonia. Repetition of Miller-type experiments with these assumed primordial atmospheres again gave biomolecules. 

Note The calculation of relative molecular mass, Mr, of organic molecules exceeding 2000 u is significantly influenced by the basis it is performed on. Both the atomic weights of the constituent elements and the natural variations in isotopic abundance contribute to the differences between monoisotopic- and relative atomic mass-based values. In addition, they tend to characteristically differ between major classes of biomolecules. This is primarily because of molar carbon content, e.g., the difference between polypeptides and nucleic acids is about 4 u at Mr = 25,000 u. Considering terrestrial sources alone, variations in the isotopic abundance of carbon lead to differences of about 10-25 ppm in Mr which is significant with respect to mass measurement accuracy in the region up to several 10 u. [41]... 

Most analytical studies using FT-ICR mass spectrometry, where ions have been produced inside (or just outside) the analyzer cell, have used lasers as ionization sources. Other than some very limited Cs secondary ion mass spectrometry (SIMS) studies [77], most research utilized direct laser desorption to form various organic [78] and inorganic [79] ions, including metal [80] and semiconductor [81] (including carbon) clusters. More recently matrix assisted laser desorption ionization (MALDI) has been used to form ions of high molecular weight from polymers [82] and many classes of biomolecules [83]. 

Starting from the identification of chiral amino acids found in meteorites, a partial transfer to other biomolecules of low ee succeeded (Breslow et al. 2010 and references of Breslow cited therein). Under solvent-free conditions followed by evaporation and heating, D-a-methyl-valine reacted with pyruvate to form D-a-alanine with a relatively low ee of 3% by way of transamination. Higher enantioselectivity was observed with sodium phenyl-pyruvate. In this reaction, the D-a-methyl-valine plays two roles. It carries out the transamination that converts the keto-acid to an amino acid, while becoming a ketone after hydrolysis. Secondly, it is the source of a proton on the alpha carbon atom of the amino acid product, delivering it stereoselectively (Breslow et al. 2010). 

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