genome and proteome

Important features of the genome and proteome:

1) Segments of nucleic acid that code for a useful sequence can be re-used, and need not arise de novo for each protein in an organism’s proteome.

2) The original genetic code probably employed 2 not 3 bases to code for each amino acid, and there were probably less than 20 constituent amino acids in primordial proteomes.

3) Many codons – the 2 or 3 base coding sequences – overlap with one another. That is, several sequences may code for a single amino acid within the polypeptide. This redundancy feature protects the proteome from random point mutations in the genome. For example, these are the triplet codons for arginine: CGU CGC CGA CGG AGA AGG

4) The function of proteins depends upon their tertiary and quaternary (3D) structure, and not on the primary (amino acid sequence) structure.

5) Homologous proteins, those that perform similar functions in different organisms, share sequences that are evolutionarily invariant, or conserved. Other amino acids may be substituted into the sequences whose sole function is to connect the important sequences without altering the 3D configuration or function of a protein.

6) Many small RNAs are important as enzymes and in epigenetic regulation – these RNAs are coded for by segments of DNA that do not code for proteins. Translation of RNA to protein is orchestrated by RNA and proteins.

7) Because the sequences of bases in RNA and one strand of DNA are complementary, the sequences of bases in RNA are equivalent to those in the other strand of DNA (with RNA's U switched to DNA's T). This means that RNA could have provided the template for encoding of its own sequences, thus eliminating any need for re-invention of a DNA code from which to transcribe RNAs.

8) The enormous number of different sequences of bases in the hypothetical 26 base RNA strand in the example demonstrates the possible ‘experiments’ that could be performed in a primordial soup mix. Remember that the example merely examined permutations and combinations for a 26 base nucleic acid polymer.

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