Methionine
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Itcysteine areonly sulfur containing amino acids thatcodedby DNA (Homocysteinean amino acidcontains sulfur, but isproductS-adenosylmethionine 1 carbon metabolismis not codedby DNA). Methionine ismethyl donor as S-adenosyl methionine (SAM). Itincorporated intoN-terminal positionall proteinseukaryotesarchaea, thoughmay be removed by post-translational modification (bacteria incorporate N-formyl methionine instead). It playsrolecysteine, carnitinetaurine synthesis bytranssulfuration pathway, lecithin production,synthesisphosphatidylcholineother phospholipids. Improper conversionmethionine can leadatherosclerosis. Methionine ischelating agent.
Most amino acids haveredundant genetic code; several different nucleotide sequences code forsame amino acid, givingdegreeerror-correction togenetic sequence, usually withthird base incodon being non-specific. Methionineoneonly two amino acids withsingle codon, AUG. (Tryptophan, encoded by UGG, isother)
