Introduction to chemistry of proteins

1.7. Amino acids

Introduction

There are approximately 300 amino acids present in various animals, plants, and microbial systems, but only 20 amino acids are coded by DNA to appear in proteins.

Cells produce proteins with strikingly different properties and activities by joining the same 20 amino acids in many different combinations and sequences. This indicates that the properties of proteins are determined by the physical and chemical properties of their monomeric units, the amino acids.

Definition

Amino acids are the basic structural units of proteins consisting of an amino group, (-NH₂) a carboxyl (-COOH) group a hydrogen (H) atom and a (variable) distinctive (R) group.

All of the substituents in amino acid are attached (bonded) to a central α carbon atom. This carbon atom is called α because it is bonded to the carboxyl (acidic) group.