Origin of Life: new commentaries (Introduction)

by David Turell , Monday, April 11, 2011, 18:13 (4954 days ago) @ David Turell

Questions about Origin of Life includes the issue of why are there 20 essential amino acids, that is acids that make all proteins, and must be eaten to be available. (Actually, in some organisms there are 22, but this is a rare requirement.) Why aren't other amino acids used? Now comes a paper that seriously questions whether these 20 were chosen by chance. The paper appears to state that these 20 are the most desirable for life, and could not happen just from chance evolution:-
Astrobiology. 2011 Mar 24. [Epub ahead of print]-Did Evolution Select a Nonrandom "Alphabet" of Amino Acids?
Philip GK, Freeland SJ.-NASA Astrobiology Institute, University of Hawaii , Honolulu, Hawaii.-Abstract
Abstract The last universal common ancestor of contemporary biology (LUCA) used a precise set of 20 amino acids as a standard alphabet with which to build genetically encoded protein polymers. Considerable evidence indicates that some of these amino acids were present through nonbiological syntheses prior to the origin of life, while the rest evolved as inventions of early metabolism. However, the same evidence indicates that many alternatives were also available, which highlights the question: what factors led biological evolution on our planet to define its standard alphabet? One possibility is that natural selection favored a set of amino acids that exhibits clear, nonrandom properties-a set of especially useful building blocks. However, previous analysis that tested whether the standard alphabet comprises amino acids with unusually high variance in size, charge, and hydrophobicity (properties that govern what protein structures and functions can be constructed) failed to clearly distinguish evolution's choice from a sample of randomly chosen alternatives. Here, we demonstrate unambiguous support for a refined hypothesis: that an optimal set of amino acids would spread evenly across a broad range of values for each fundamental property. Specifically, we show that the standard set of 20 amino acids represents the possible spectra of size, charge, and hydrophobicity more broadly and more evenly than can be explained by chance alone. Key Words: Astrobiology-Evolution-Molecular biology-Modeling studies. Astrobiology 11, xxx-xxx.-PMID: 21434765 [PubMed - as supplied by publisher]-(My bolding)