Genetic code: Difference between revisions

Revision as of 14:22, 20 February 2003

Revision as of 01:40, 12 March 2003

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It is notable that the standard genetic code contains features which provide for basic forms of [[error correction]]. Many codons which differ by only one base still encode the same amino acid and most often the single base that differs is the last one, which happens to be the base which is most often misread by the translation process. Furthermore, amino acids which tend to occur more frequently in proteins on average tend to have more codons which code for them.

Numerous variations on the standard genetic code are found inside [[mitochondrion|mitochondria]], energy-burning organelles that were probably derived from symbiotic bacteria. The [[Ciliophoraciliate]] or ciliate protozoa also show some variation in the genetic code: UAG and often UAA code for Glutamine, a variant also found in some [[green algae]], or UGA codes for Cysteine. One more variant is found in some species of the [[yeast]] ''[[Candida]]'', but interestingly not in all, where CUG codes for Serine. There are also a few "non-standard" amino acids which are substituted for some stop codons in some species of [[bacteria]] and [[archaea]]; UGA can code for [[selenocysteine]] and UAG can code for [[pyrrolysine]]. Other non-standard amino acids and codon interpretations may be present but currently unknown.

Despite these variations, the genetic code used by all known life on Earth displays a very large degree of similarity. Since there are many possible genetic codes that are thought to have similar utility to the one used by Earth life, the theory of [[evolution]] suggests that the genetic code was established very early in the history of life.