C.2.1

State the basic structure of a 2-amino acid (or alpha amino acid)
The basic structure of a 2-amino acid is **amine group** and **carboxylic acid / carboxyl group **. These two groups of atoms are called functional groups. A **functional group** is a group of atoms that reacts in a chemical reaction. The R group refers to different group of atoms. Each R group gives rise to a specific amino acid. For example if the R group is a -CH3 or a methyl group, the amino acid is alanine.



//Figure 1: general structure of an amino acid//

[[image:Alanine.jpg width="301" height="139" align="left"]]
//Figure 2: amino acid alanine//

There are 20 common 2-amino acids and each one differs in their R group. The simplest amino acid is glycine. It R group is a H atom.

2-amino acids contain an **asymmetric or chiral carbon atom**, a carbon atom that has four different groups attached to it. In 2-amino acids the central carbon atom is chiral. Molecules that have a chiral carbon atom can exits as **mirror images** of each other and the two different isomers are optically active with plane polarized light. Normal light consists of electromagnetic radiation which vibrates in all planes. When it is passed through a polarizing filter the waves only vibrate in one plane and the light is said to be polarized. The two mirror images of a 2-amino acid, known as **enantiomers**, both **rotate the plane of polarized light**. One enantiomer rotates it to the left and the other to the right. Apart from their behavior towards polarized light entantiomers have **identical physical properties**.

Figure: Mirror images of a generalized 2-amino acid showing the two enantiomers