Genetic code refers to the instructions contained in a gene that tell a cell how to make a specific protein. Each gene's code uses the four nucleotide bases of DNA: adenine (A), cytosine (C), guanine (G) and thymine (T) — in various ways to spell out three-letter "codons" that specify which amino acid is needed at each position within a protein.
The genetic code is the means by which the genetic information in DNA is used to control the manufacture of specific proteins in cells. The code consists of a series of triplets (see codons) of bases in DNA, from which is transcribed a complimentary sequence of codons in messenger RNA (mRNA). The sequence of these codons determines the sequence of amino acids which go to make a particular protein. Using all the triplet combinations of the four bases in DNA and mRNA gives 64 different possible codes.