Every living system has a blueprint for replication, or making copies of itself.
This blueprint is commonly called heredity. The key structure of the hereditary process is the long, spiral DNA molecule. The strands are made up of varying sequences of chemical groups which are called nucleotides. DNA contains the genetic code for making proteins from smaller molecules called amino acids. Thus, a base triplet corresponds to a particular amino acid in the same way that a unit of the Morse telegraph code corresponds to an alphabet letter.