A codon is a sequence of three nucleotides in DNA or RNA that corresponds to a specific amino acid or signals the termination of protein synthesis. Each codon acts as a unit of genetic information that instructs the cell to add a particular amino acid to a growing protein chain or to stop protein production. There are 64 possible codons: 61 code for amino acids, and 3 serve as stop signals. For example, the codon AUG codes for the amino acid methionine and also signals the start of protein synthesis. Codons form the basis of the genetic code, which is read by the cellular machinery to build proteins according to the instructions encoded in genes