Amino Acids: Physicochemical Properties

Definition

Amino acids are the building blocks of all peptides and proteins and determine many of their important properties. This paper describes the physicochemical properties of amino acids and tries to shed light on their role as the constituents of living cells, the proteins.

α-Amino acids are molecules that possess an amino group (-NH₂) and a carboxylic group (-COOH) attached to the same tetrahedral carbon atom, called an α-carbon (Fig. 1a). The α-amino acids differ from one another by distinct R-groups (referred to as side chains) that are attached to the same α-carbon. Table 1 gives the structures and names of the 20 most common amino acids found in proteins. Those marked ‘e’ in Table 1 are the essential amino acids, which are not available to animals by biosynthesis and must therefore be provided in the diet.

Figure 1

Chemical structure (a) and dipolar-ion form (b) of an amino acid. R represents the side chain group.