Amino Acids Notes part1

Amino acids are monomeric units of proteins. Proteins are high molecular weight organic polymer. Although about 200 to 300 amino acids occur in nature, only 20 of them are seen in human body.

Amino acids are relatively simple molecules containing both an amine group and an acid group. The biologically important amino acids are the alpha-amino acids that have the amine and acid groups attached to the same carbon atom. There are more than 300 known natural amino acids; however, only 20 of them are used in protein synthesis. Francis Crick (who with James Watson determined the structure of DNA) labeled this set of amino acids the magic 20. Other amino acids are found in certain proteins, but in almost all cases these additional amino acids result from the modification of one of the magic 20 after the protein formed.

Definition:

“A substance which has both carboxyl and amino group in the same molecule is called ‘amino acid’. The amino group is basic while the carboxyl group (-COOH) is acidic in nature”.

General Structure:

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

All proteins are polymers of amino acids and all these acids except two have an amino group attached to the carbon atom next to the carboxyl group. The general formula of the amino acid is ..

Rules to write the Amino acids:

We should write the general formula by using the given points:

• We should write the Carboxyl group on Top side of the center  carbon (asymmetric carbon)

• We should write the Amino group on Left side of the centre carbon (asymmetric carbon).
• We should write the hydrogen atom on Right side of the centre carbon (asymmetric carbon).
• We should write the ‘R’ side chain at the Bottom of the centre carbon (asymmetric carbon).

The amino acids are termed as α-amino acids, if both the carboxyl and amino groups are attached to the same carbon atom. The amino acids mostly exist in the ionized form in the biological system.

Stereochemistry:

Carbon atom is attached to four different groups, which is simply called “asymmetric” and therefore exhibits optical isomerism. All amino acids contain asymmetric carbon, except Glycine. (Glycine is Optically inactive compound).

D & L Forms:

Amino acids can be shown in two different forms depends on the position of amino group on the asymmetric carbon atom. When the amino group situated on the left side, which is L-form. When the amino group situated on the sight side, which is D-form. All naturally occurring amino acids are in L-configuration.

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Lecture Series on BioChemistry I by Prof.S.Dasgupta, Dept of Chemistry, IIT Kharagpur.