Another claim often heard is that there is a "life sequence" of 400 proteins, and that the amino acid sequences of these proteins cannot be changed, for organisms to be alive.
This, however, is nonsense. The 400 protein claim seems to come from the protein coding genome of Mycobacterium genetalium, which has the smallest genome currently known of any modern organism. However, inspection of the genome suggests that this could be reduced further to a minimal gene set of 256 proteins . Note again that this is a modern organism. The first protobiont/progenote would have been smaller still, and preceded by even simpler chemical systems.
As to the claim that the sequences of proteins cannot be changed, again this is nonsense. There are in most proteins regions where almost any amino acid can be substituted, and other regions where conservative substitutions (where charged amino acids can be swapped with other charged amino acids, neutral for other neutral amino acids and hydrophobic amino acids for other hydrophobic amino acids) can be made. Some functionally equivalent molecules can have between 30 - 50% of their amino acids different. In fact it is possible to substitute structurally non-identical bacterial proteins for yeast proteins,, and the organisms live quite happily.
The "life sequence" is a myth!
