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The amino acids are a group of organic compounds containing two functional groups - amino and carboxyl. The amino (–NH2) group is basic while the carboxyl (–COOH) group is acidic in nature. Amino acids are the building blocks of proteins.

The amino acids are called as α-amino acids when both the amino and carboxyl groups are attached to the same carbon atom. The α-carbon atom binds to a side chain which is represented by R and is different for each of the 20 amino acids. In the biological system, amino acids mostly exist in ionized form.

The amino acids (except glycine) have asymmetric carbon atom i.e. the carbon atom is attached to four different groups (R, H, COO , NH3+). Thus all amino acids except glycine have optical isomers.

Simple proteins contain only amino acids, while conjugated proteins have additional groups. Amino acids may be neutral, acidic or basic. As mentioned earlier, each amino acid has one basic amino group (–NH2) and one acidic carboxyl group (–COOH). Neutral amino acids have one amino and one carboxyl group. Acidic amino acids have an additional acidic group i.e. two carboxyl groups and one amino group. Basic amino acids have an additional basic group i.e. two amino groups and one carboxyl group. 

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