Enzymes are biocatalysts which are crucial for nearly all chemical reactions taking place in living organisms. Their role is to increase reaction rates by some million-fold. Indeed, chemical reactions within a living cell would hardly take place at all in the absence of enzymes. Without enzymes there would simply be no life. So far all enzymes have been considered to be proteins.
Proteins are large molecules which are built from a repertoire of twenty amino acids.
Normally a protein is composed as a string of several hundreds of amino acids. The remarkable range of functions mediated by proteins results from different amounts and combinations of these twenty, which in turn are determined by the genetic message in the DNA molecules. The DNA molecules are located in the chromosomes. Each DNA molecule consists of two very long strands arranged as a double helix. Each strand is composed of the molecular letters of heredity.