Proteins are organic molecules that are vital to the structure and function of living organisms. The underlying elements that make up all proteins include carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and in some cases, sulfur (S). These elements combine to form amino acids, which are the building blocks that, when combined, make up the more complex protein compounds (Source: Keeton).
Amino acids are characterized by having a carboxyl group (—COOH) and an amino group (—NH2). In addition to the carboxyl group and the amino group, amino acids also have side chains (or 'R groups') that can be simple or extremely complex. It is these R groups that give each amino acid a unique chemistry (Source: Keeton).
The 20 Amino Acids
The twenty amino acids commonly found in proteins include:
- nonpolar amino acids: glycine (gly), alanine (ala), valine (val), leucine (leu), isoleucine (ile), methionine (met), phenylalanine (phe), tryptophan (trp), and proline (pro)
- polar amino acids: serine (ser), threonine (thr), cystein (cys), tyrosine (tyr), asparagine (asn), and glytamine (gln)
- charged amino acids: aspartic acid (asp), glutamic acid (glu), lysine (lys), arginine (arg), and histidine (his)
The Anatomy of a Protein
Amino acids combine into small chains via chemical reactions called 'condensation reactions' in which the carboxyl group and the amino group bond to one another. These small chains that contain a few amino acids linked together are called polypeptide chains (the individual amino acids are called petides). Polypetide chains, in turn, combine into the more complex structures know as proteins (Source: Keeton).
Source: Keeton, W.T. and J.L. Gould. 'Biological Science (4th Edition)'. W.W. Norton & Co Ltd. New York. 1986.
