Chemical Structure, Bonding
Amino acids are organic compounds made of carbon, hydrogen, oxygen, nitrogen and, in a few cases, sulfur. The basic structure of an amino acid molecule consists of a carbon atom that is bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom and a fourth group that differs from one amino acid to another and is often referred to as the -R group or the side chain. The -R group can vary widely and is responsible for the differences in the chemical properties. The name, amino acid, comes from the amino group and the acid group which are the most reactive parts of the molecule. The amino acids that are important in the biological world are referred to as a-amino acids because the amino group is bonded to the a-carbon atom, that is, the one adjacent to the carboxyl group.
A chemical reaction that is characteristic of amino acids involves the formation of a bond, called a peptide linkage, between the carboxyl group of one amino acid and the amino group of a second amino acid. Very long chains of amino acids can bond together in this way to form proteins. The importance of the amino acids in nature arises from their ability to form proteins, which are the basic building blocks of all living things.
The specific properties of each kind of protein are largely dependent on the kind and sequence of the amino acids in it. Other chemical behavior of these protein molecules is due to interactions between the amino and the carboxyl groups or between the various -R groups along the long chains of amino acids in the molecule. These chemical interactions confer a three-dimensional configuration on the protein, which is essential to its proper functioning.