Proteins are manufactured according to the genetic code which is located in the DNA. It is then copied by the mRNA in the process of transcription. The mRNA travels to a ribosome, where this code is translated and a protein is manufactured. If there are 51 amino acids translated on the ribosome from this code, then each amino acid in turn, is manufactured according to a codon which is a triplet of 3 nitrogenous bases. If you multiply 51 amino acids by 3, then you will arrive at 153 bases needed to code for insulin. These bases located on a DNA strand will contain the instructions to produce the protein insulin.