Cysteine is an amino acid.
The molecular formula of cysteine is C3H7NO2S
Amino acids generally are explained further in the column on the rightin further detail below. Briefly, there are two types of amino acid:
- Those that can be synthesized by the body itself (non-essential amino acids), and
- those that, although necessary for the healthy growth or maintenance of the body, cannot be produced by the body itself.
This second type of amino acids are called essential amino acids, and are also referred to as indispensible amino acids in some textbooks.
Cysteine is a "non-essential" or "dispensible" amino acid because, although its presence in an appropriate quantity is important for good health, the human body can produce this chemical from an excess of certain other amino acids in the body. Therefore it is not essential as a part of the diet.
Cysteine is sometimes described as a "natural sulphur antibiotic", which can be explained by its sulphur content - as indicated in its chemical formula. The presence of this sulphur component is responsible for some of the main functions of cysteine. For example, the disulphide (S-S) links between adjacent molecules in the polypeptide chains formed by cysteine help to form the 3-dimensional structures of the proteins of which they are part.
Cysteine is also an important part of many enzymes.
For further information about amino acids in general, see Amino Acids.