Evolution protein biosynthesis

Numerically the largest group of signaling substances, these arise by protein biosynthesis (see p. 382). The smallest peptide hormone, thyroliberin (362 Da), is a tripeptide. Proteohormones can reach masses of more than 20 kDa—e.g., thyrotropin (28 kDa). Similarities in the primary structures of many peptide hormones and proteohormones show that they are related to one another. They probably arose from common predecessors in the course of evolution. 

Protein synthesis is a central function in cellular physiology and is the primary target of many naturally occurring antibiotics and toxins. Except as noted, these antibiotics inhibit protein synthesis in bacteria. The differences between bacterial and eukaryotic protein synthesis, though in some cases subtle, are sufficient that most of the compounds discussed below are relatively harmless to eukaryotic cells. Natural selection has favored the evolution of compounds that exploit minor differences in order to affect bacterial systems selectively, such that these biochemical weapons are synthesized by some microorganisms and are extremely toxic to others. Because nearly every step in protein synthesis can be specifically inhibited by one antibiotic or another, antibiotics have become valuable tools in the study of protein biosynthesis. 

The general arguments about the antiquity of cofactors apply to PLP. The nonenzymatic synthesis of pyridoxal under prebiotic conditions is considered possible, whereas the presence of a 5 phosphate group could hint to an ancestral attachment of the cofactor to RNA molecules. " Furthermore, there are specific grounds to assume that PLP arrived on the evolutionary scene before the emergence of proteins. In fact, in current metabolism, PLP-dependent enzymes play a central role in the synthesis and interconversion of amino acids, and thus they are closely related to protein biosynthesis. In an early phase of biotic evolution, free PLP could have played many of the roles now fulfilled by PLP-dependent enzymes, since the cofactor by itself can catalyze (albeit at a low rate) reactions such as amino acid transaminations, racemizations, decarboxylations, and eliminations. " This suggests that the appearance of PLP may have preceded (and somehow eased) the transition from primitive RNA-based life forms to more modern organisms dependent on proteins. 

Gene A segment of DNA containing all information for the regulated biosynthesis of an RNA product, including promoters, exons, introns, and other untranslated regions that control expression. Fundamental physical and functional unit of heredity and evolution. A gene is an ordered sequence of nucleotides located on a specific chromosomal locus that encodes particular products (i.e., RNA molecules, proteins) (see comment at amino acids). 

Three pieces of evidence are cited in support of an RNA World. Firstly, some 17 RNA ribozyme catalysts have been discovered that produce a diverse array of organic molecules, including peptide bond formation. Second, the ability to form the peptide bond and build proteins may lead to a complex evolution favoured by the proximity of proto-proteins, producing enhanced reaction efficiency. Finally, RNA is the intermediate in the biosynthesis of DNA, suggesting that it must have preceded DNA in the evolutionary process. 

An attractive hypothesis is the independent evolution in bacteria of their diffusible individualites and the currently recognized secondary metabolic pathways, in parallel with their surface components and their biosynthesis. An indicator for this would be the use of the same gene pool. The theory would include all substances that play a role in the build-up of glycan and other modified surface layers, lipids, murein, (glyco-) proteins (e.g., S-layers), polysaccharides, teichoic... 

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