Proteins are another major group of organic compounds in addition to carbohydrates and lipids.
Composed of amino acids, proteins serve in both structural and physiological roles. In their structural role,
proteins compose many of the cellular building materials. In their physiological roles, proteins are enzymes that
speed up many biochemical reactions. Some proteins, in muscle, aid in movement, while other proteins, as antibodies, help defend the body.
A protein is formed when amino acids are joined. An amino acid contains three main groups connected to one central carbon atom.
These three groups are the carboxyl group (-COOH), the amino group (-NH2), and the side chain (R group).
The bonds that join amino acids are called peptide bonds which form between the carboxyl and amino groups. A pair of
linked amino acids is called a dipeptide. If you add another amino acid, it now becomes a tripeptide.
Polypeptides consist of between 10 and 2000 amino acids.