Proteins play a crucial role in almost all fundamental processes in the living cell. Although the genetic information is encoded in nucleic acids, the mechanisms of DNA replication and of gene expression are controlled by proteins. The enzymes that mediate the chemical reactions necessary for life are proteins, as are several of the hormones that control the biochemical balance in complex organisms. Peptides are simply smaller versions of proteins. Their three-dimensional structures tend to be less well defined, but many, such as the peptide-hormones vasopressin, oxytocin, and calcitonin, the neuroactive peptides found in the brain, and the toxins of certain animals and bacteria, are biologically important. In addition to chemical synthesis, biotechnological techniques now provide an alternative and often very efficient means of producing proteins. In favorable cases they are currently the best way of producing useful amounts of material for research and industrial purposes.