Proteins are polymers consisting of amino acids linked together by peptide bonds. The genetic code for building any protein is located in an organism's DNA in the cell's nucleus.
Messenger RNA is able to copy the DNA code in a process called transcription and this transcript travels out of the nucleus to the cytoplasm where a ribosome attaches to it and decodes the transcript in a process called translation. Every three nitrogenous bases is a triplet known as a codon. Each codon is the instructions to form a particular amino acid to be added to the growing polypeptide chain.
Human insulin is a small protein molecule which has two chains attached by disulfide linkages. The first chain has 30 amino acids and the second has 21 amino acids. Since three nitrogenous bases are in each amino acid, there are 90 nitrogenous bases to code for the first chain and 63 to code for the second chain. The sum total of nitrogenous bases to code for the protein insulin is 153.
I have included a link to show insulin's structure and information on how the DNA code is used to produce insulin using recombinant DNA technology.