Turned up to eleven: Fair and Balanced

Friday, March 22, 2002

I am working on some thoughts on Lagniappe's comments on life's origins and chemical "handedness" (chirality). I will post more on this, but I think many chemists and biologists have been intrigued by this notion that life is utterly dominated by L-form amino acids. One side note, though, before I get into the more lengthy discussion. Bacterial cell walls contain several D-amino acids (D-Glutamate and D-alanine, for example), as well as L-forms, so it is possible that the weighting (all proteins are made of L-amino acids) is due to the evolution of the translation machinery (which turns strands of RNA, derived from the genome by a process called transcription, into proteins), rather than the prevalent mix of amino acids in the "primordial soup). The peptides in the bacterial cell wall are used for cross-linking strands of sugars into a mesh (called the "murein sacculus" which is one of my favorite evocative science terms) that protects the salty inside of the cell from osmotic pressure. I don't think that there is any clearly understood reason why bacteria use D-form(ed) (heh, heh) amino acids for this function rather than the L-forms used in protein synthesis, but it is interesting to note that the incredible abundance of bacteria makes D-form amino acids more widespread in the biosphere than you might think.