Genetic code: Difference between revisions

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The '''genetic code''' is a [[mapping]] that [[biological cell]]s use to [[translation (biology)|translate]] sequences of three [[nucleotide]] bases, called '''codons''' or '''triplets''', into [[amino acid]]s. Nearly all living things use the same genetic code, called the '''standard genetic code''', and all use small variations of it. The code is followed repeatedly, creating many amino acids strung together into a [[protein]].

This translation is the latter stage of [[protein biosynthesis]]. The first stage is [[transcptiontranscription]], where a sub-sequence of [[DNA]] called a [[gene]] is rewritten into an [[RNA]]. An RNA is a sequence of repeating nucleotide bases: [[adenine]], [[guanine]], [[cytosine]] and [[uracil]]. The RNA is divided into non-overlapping groups of three bases, called codons. Each codon is then translated to a particular amino acid. Thus a codon is said to code for that amino acid in the genetic code. There are 4³ = 64 codons. For example, the RNA sequence UUUAAACCC contains the codons UUU, AAA and CCC, each of which specifies one amino acid. So, this RNA sequence represents a protein sequence, three amino acids long. ([[DNA]] is also sequence of nucleotide bases, but there [[thymine]] takes the place of uracil.)

The standard genetic code is shown in the following tables. [[#Table 1: Codon Table|Table 1]] shows what amino acid each of the 64 codons specifies. [[#Table 2: Reverse Codon Table|Table 2]] shows what codons specify each of the 20 standard amino acids involved in translation. These are called forward and reverse codon tables, respectively. For example, the codon GAU represents the amino acid [[asparagine]] (Asp), and [[cysteine]] (Cys) is represented by UGU and by UGC.