The hereditary instructions in DNA specify the sequence of amino acids in proteins. Proteins are the building blocks of cells and they perform a wide range of functions, such as catalyzing chemical reactions, transporting molecules, and providing structural support. The sequence of amino acids in a protein is determined by the sequence of nucleotides in the DNA molecule. Each codon, which is a sequence of three nucleotides, corresponds to a specific amino acid. The genetic code is the set of rules that relates the sequence of nucleotides in DNA to the sequence of amino acids in proteins.