Coenzymes
The chemical reactivity and specificity of an enzyme largely depends on its catalytic site, made up of the side chains of chiral amino acids (glycine is the only non-chiral amino acid, the remaining 19 amino acids are chiral in nature). However, sometimes the side chains of chiral amino acids are insufficient and the enzyme may need a non-polypeptide molecule to bind on its surface thus enabling it to function as an enzyme. These non-polypeptide molecules serve as ligands and are called coenzymes. The coenzymes are therefore defined as small molecules that are associated with enzymes, and are essential for the activity of enzymes. Some of these coenzymes are involved in group transfers.