Page "Biochemistry" Paragraph 38

In essence, proteins are chains of amino acids.

An amino acid consists of a carbon atom bound to four groups.

One is an amino group, — NH < sub > 2 </ sub >, and one is a carboxylic acid group, — COOH ( although these exist as — NH < sub > 3 </ sub >< sup >+</ sup > and — COO < sup >−</ sup > under physiologic conditions ).

The third is a simple hydrogen atom.

The fourth is commonly denoted "— R " and is different for each amino acid.

There are twenty standard amino acids.

Some of these have functions by themselves or in a modified form ; for instance, glutamate functions as an important neurotransmitter.