Chemistry will tell you that an amino acid is any molecule that has both carboxylic acid and amino functional groups. They are the basic building units of a protein. In biochemistry, the shorter and more general term is used to refer to alpha amino acids. Those are amino acids wherein the amino and carboxylate -functionalities are attached to a common carbon. Amino acids’ residue is what’s left of an amino acid once a water molecule has been lost in the formation of a peptide bond. Peptides are polymer chains which form the protein in our bodies.
Even though only 20 amino acids are genetically encoded, over one hundred have been found in nature. Some of these have been seen in meteorites, especially in a type called carbonaceous chondrites. Microorganisms and plants can often produce somewhat uncommon amino acids, which are located in peptidic antibiotics. Lanthionine is a sulfide-bridged alanine dimer found along with unsaturated amino acids in lantibiotics, which are antibiotic peptides of microbial origin.
As well as protein synthesis, amino acids have some other biologically important jobs. Glycine, and glutamate, are used as neurotransmitters as well as standard amino acids in proteins. Many amino acids take on the role of synthesizing other molecules, such as tryptophan, which is a precursor of the neurotransmitter serotonin, and glycine.
