Genetic code: Difference between revisions

Revision as of 10:37, 30 January 2004

Revision as of 10:42, 30 January 2004

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In classical genetics, the stop codons were given names - UAG was amber, UGA was opal, and UAA was ocher. These names were originally the names of the specific genes in which mutation of each of these stop codons was first detected. Translation starts with a chain initiation codon (start codon). But unlike stop codons, these are not sufficient to begin the process; nearby initiation sequences are also required to induce transcription into mRNA and binding by [[ribosome]]s. The most notable start codon is AUG, which also codes for methionine. CUG and UUG, and in [[prokaryotes]] GUG and AUU, also work.

It is notable that the standard genetic code containshas basic features of basic [[error correction]]. Many codons which differ by only one base codes for the same amino acid, and most often the base that differs is the last base, which happens to be the base which is most often misread in 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 of the standard genetic code are found in [[mitochondrion|mitochondria]], energy-burning [[organelles]]. [[Ciliate]] [[protozoa]] also have some variation in the genetic code: UAG and often UAA code for Glutamine (a variant also found in some [[green alga]]e), or UGA codes for Cysteine. Another variant is found in some species of the [[yeast]] [[candida]], where CUG codes for Serine. In some species of [[bacteria]] and [[archaea]], a few non-standard amino acids are substituted for standard stop codons; UGA can code for [[selenocysteine]] and UAG can code for [[pyrrolysine]]. There may be other non-standard amino acids and codon interpretations but are not known.