An amino acid molecule has the general formula NH2CHRCOOH, where "R" is any one of a number of side groups. Amino acids are building blocks (small molecules that link together to form long chains) of proteins.
There are 20 amino acids found in proteins, called primary amino acids. Non-essential amino acids are those made by the human body, while essential amino acids are only obtained from protein in the foods that we eat.
Source: GreenFacts
An illustration of amino acid can be found in the NHGRI Talking Glossary of
Genetic Terms: NHGRI illustration
Français: Acide(s) aminé(s)