Amino acids are transcribed and translated from DNA molecules consist of nucleotides. There are 4 kind of nucleotides (namely adenine, cytosine guanine and thymine), however, there are 20 kinds of amino acid so each nucleotide cannot correspond directly to each amino acid.
Therefore, solve this problem, the genetic code uses a many-to-one mapping for most amino acids, with the exception for Met and Trp which respectively correspond to a codon. This means the genetic code is degenerate. (e.g. GGU GGC GGG GGA all code for glycine)
- ↑ Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K. and Walter, P. (2008) 'Molecular Biology of the Cell', in 5th edGarland Science, pp. 367