Protein functional redundancy

Protein functional redundancy - Protein functional...

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Protein functional redundancy The support for common descent given by studies of molecular sequences can be phrased as a deductive argument. This argument is unique within this FAQ, as it is the only instance we can directly conclude that similarity implies relatedness. This conclusion depends upon the similarity of biological structures within a specific context: the similarity observed between ubiquitous genes from different species. The following discussion is somewhat technical, so it is first presented in the outline of a deductive argument, which makes the logical thread easy to follow. Here are listed the premises of the argument followed by the conclusion and further discussion. The gist of the argument: (P1) Ubiquitous genes : There are certain genes that all living organisms have because they perform very basic life functions; these genes are called ubiquitous genes . (P2) Ubiquitous genes are uncorrelated with species-specific phenotypes : Ubiquitous genes have no relationship with the specific functions of different species. For example, it doesn't matter whether you are a bacterium, a human, a frog, a whale, a hummingbird, a slug, a fungus, or a sea anemone - you have these ubiquitous genes, and they all perform the same basic biological function no matter what you are. (P3) Molecular sequences of ubiquitous genes are functionally redundant : Any given ubiquitous protein has an extremely large number of different functionally equivalent forms (i.e. protein sequences which can perform the same biochemical function). (P4) Specific ubiquitous genes are unnecessary in any given species : Obviously, there is no a priori reason why every organism should have the same sequence or even similar sequences. No specific sequence is functionally necessary in any organism - all that is necessary is one of the large number of functionally equivalent forms of a given ubiquitous gene or protein. (P5) Heredity correlates sequences, even in the absence of functional necessity : There is one, and only one, observed mechanism which causes two different organisms to have ubiquitous proteins with similar sequences (aside from the extreme improbability of pure chance, of course). That mechanism is heredity. (C) Thus, similar ubiquitous genes indicate genealogical relationship : It follows that organisms which have similar sequences for ubiquitous proteins are genealogically related. Roughly, the more similar the sequences, the closer the genealogical relationship. Discussion: The amino acid sequences of proteins are often used to establish the phylogenetic relationships of species. Sequence studies with functional genes have centered on genes of proteins (or RNAs) that are ubiquitous (i.e. all organisms have them). This is done to insure that the comparisons are independent of the overall species phenotype. For example, suppose we are comparing the protein sequence of a chimpanzee and that of a
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Protein functional redundancy - Protein functional...

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