Amino Acids

Nitrogen-containing compounds are another large class of organic compounds. The most important
nitrogen-containing functional group is the amine group, –NH 2 , which is found in amino acids, the
basic building blocks of proteins.

BASIC CONCEPT

Proteins    are made    up  of  amino   acids.

An amino acid contains an amine group, a carboxyl group, and a side group R that is different for
different amino acids. In fact, what R is essentially defines what amino acid it is. It can be as simple
as just another hydrogen atom (in which case the amino acid is glycine), or it can be more complex,
with distinctive functional groups of its own. It may even contain atoms other than carbon, oxygen,
and nitrogen: Cysteine and methionine are two amino acids that contain sulfur atoms in their side
chains.

There are 20 naturally occurring amino acids, and these amino acids can be joined together by
bonds called peptide bonds to form small chains of amino acids known as peptides. Two amino
acids joined together form a dipeptide, three form a tripeptide, and many amino acids linked
together form a polypeptide. At some point (the exact boundary is not well defined), the
polypeptide becomes long enough and we call it a protein. Proteins serve many diverse functions in
biological systems, acting as enzymes, hormones, elements of cell structure, et cetera. The protein’s
amino acid sequence—the precise ordering and identity of each amino acid in the protein—is called
its primary structure and determines the shape and function of the protein. The actual prediction of
a protein’s shape from its primary sequence is an active area of research.