Introduction to amino acids

a-amino acids are the building blocks for polypeptides and proteins.
All aminocids (at the exception of proline) have the following structure:


in which the carbon Ca is attached to both an amino (-NH2) and a carboxyl group (-COOH). R is the part of the structure varying from amino-acid to amino-acid and are highlighted in blue in the other pages of this site.
The organic functional groups pages describes in more details amines and carboxylic acids.

There are a total of 20 amino acids. amino acid can be divided into 4 categories depending on the side chain side chain.

 Acidic side chain  Asp, Glu 
 Basic side chain  Lys, Arg, His 
 Polar, uncharged side chain  Ser, Thr, Tyr 
 Cys, Asn, Gln 
 Non polar side chain  Gly, Ala, Val 
 Leu, Ile, Phe 
 Trp, Pro, Met 

To form peptides or proteins,the carbonyl (-COOH) group of one amino-acid reacts with the amino group (-NH2) of a second amino acid to create an amide group with the liberation of water (H2O). the following animation illustrate the creation of a dipeptide


All material copyright USC Department of Chemistry 1999