Wednesday, January 21, 2009
Left is left. Chapter two
I looked into the reason for the predominance of left-handed amino acids on earth some more. There are some theories on how it happened but none of them seem to hold water. One is that meteors seeded left handed amino acids on earth. Some types of polarized light destroys one or the other of the amino acids and it is possible that, on passing neutron stars, the meteor was left with mostly left handed amino acids which then plunged to earth. Another possibility is that amino acids formed on earth and then the earth was bombarded with polarized light from a neutron star to select out one of the orientations. There is another thought that beta decay could result in more left handed amino acids. It may have been a polymer that acted as a template or a transfer RNA that bound only left handed amino acids. There are a few other ideas but none of the theories have had enough substantial evidence to become more than just ideas. The problem remains.
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Hi,
ReplyDeleteI believe you overlook a pretty simple explanation. The basis lies in the likelihood that solid-phase catalysts were the "starters" for primitive quasi-metabolism, much as modern proteins (also microscopic solid-phase catalysts) are the drivers of metabolism in living things today.
You can demonstrate this for yourself by placing your finger (and thumb) tips from your left (or right, it doesn't matter) hand on a piece of paper and marking the thumb and any two fingers. Now try to fit the same two fingers and thumb from the other hand on these marks - it won't work. The "solid phase" (paper) automatically differentiates between your left and right hands. It's inevitable.
The same principle was in force at the dawn of life. Once you have asymmetric molecules (another inevitability) and solid-phase catalysts, this is the only possible outcome.
I haven't heard of this. Are there papers/articles you could recommend? I'd like more details. Why are there right handed amino acids in bacteria if the catalysts selected for all left handed then?
ReplyDeleteThe exercise I describe explains the concept that is found in any biochemistry textbook. The concept applies to any line of reasoning (in terms of the OOL) that involves catalysts.
ReplyDeleteAs for D-amino acids in bacteria, these are not used for protein synthesis. There is no reason why enzymes that make cell walls (this is where D-amino acids are used) should not use D-amino acids. This is a different set of enzymes than those used for protein synthesis.
Thanks again. I'll look it up.
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