amino acid

Amino acids are small molecules that are the building blocks of proteins. Proteins serve as structural support inside the cell and they perform many vital chemical reactions. Each protein is a molecule made up of different combinations of 20 types of smaller, simpler amino acids. Protein molecules are long chains of amino acids that are folded into a three-dimensional shape.

Chemically, an amino acid is a molecule that has a carboxylic acid group and an amine group that are each attached to a carbon atom called the α carbon. Each of the 20 amino acids has a specific side chain, known as an R group, that is also attached to the α carbon. The R groups have a variety of shapes, sizes, charges, and reactivities. This allows amino acids to be grouped according to the chemical properties of their side chains. For example, some amino acids have polar side chains that are soluble in water; examples include serine, threonine, and asparagine. Other amino acids avoid water and are called hydrophobic, such as isoleucine, phenylalanine, and valine. The amino acid cysteine has a chemically reactive side chain that can form bonds with another cysteine. Amino acids can also be basic, like lysine, or acidic, like glutamic acid. The sequence and interactions between the side chains of these different amino acids allow each protein to fold into a specific three-dimensional shape and perform biological functions.