A codon is a set of three consecutive nucleotides in mRNA (messenger RNA) that corresponds to a specific amino acid or serves as a start or stop signal during protein synthesis. The sequence of codons in mRNA determines the sequence of amino acids in a protein. Each codon codes for a specific amino acid or a signaling function, and the genetic code is the set of rules that relate the nucleotide sequence of codons to the amino acid sequence of proteins.
