by C.V.Rajan

Created on: January 28, 2009

What are amino acids?

Amino acids are the basic structural and functional units of all proteins. The primary structure of all proteins is composed of a linear chain of amino acids linked via the peptide bond. Amino acids are an integral part of various other biomolecules like heme and a number of co-enzymes. Twenty amino acids are used by the body for synthesis of various molecules.

Amino acids are classified as Essential and Non-Essential amino acids. Essential amino acids are termed essential not because of any additional importance but because they cannot be synthesized by the body. Human beings can synthesize only 12 amino acids and need the others to be supplemented by their diet. The essential amino acids for humans are Isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

Essential amino acids play an important role to increase the net protein utilization (which is a ratio of mass of amino acids converted to protein to mass of amino acid consumed). If
the diet does not have a proper balance of essential amino acids in it, the body deaminates amino acids (that is, remove the amino group in the amino acids), converting them to only fats and carbohydrates. In other words, intake of essential amino acids through food is very important for the health of the body.

Apart from these 20 standard amino acids there exist a few non-standard amino acids which are found in proteins after post-translational modifications (last step in protein synthesis which imparts functional specificity to the proteins). The dietary requirement of the various amino acids depends on age, health and other factors of the individual.

Structure of amino acids:

All amino acids consist of an amino group (-NH2) connected to a carboxyl group (-COOH) via a central carbon atom. Attached to the central carbon atom is a variable group (denoted as R) which gives uniqueness to each amino acid. The differences in R groups have a major impact on the structure of the proteins formed by the amino acids. These R groups are responsible for the various physical and chemical properties of amino acids.

Functions of amino acids:

Functions inside the body:

- Amino acids are essentially building blocks of human body.

- Amino acids are used to synthesize various proteins like enzymes and hormones.

- Some amino acids are also used as a source of energy when they get oxidized to urea and carbon dioxide.

- Amino acids (with glucogenic R groups) can be converted to glucose by a process known as gluconeogenesis.

- Amino acids aid in regulating processes related to gene expression like mRNA translation.

- Amino acids which are not used in the synthesis of proteins, known as non-protein amino acids are used in the synthesis of other important molecules in the body like neurotransmitters, polyamines, precursors for nucleotides, nitric oxide, heme etc.

- Certain non standard amino acids also play important functions like protection against herbivores in plants.

Industrial Applications:

- Amino acids are major additives to animal feed in dairy industry.

- Amino acids are used as artificial agents like flavor enhancer and artificial sweetener in food industry.

- They are used in pharmaceutical industry for the treatment of Parkinson's disease and depression related disorders.

- Use of Amino acids as potential source for biodegradable plastics is under research.

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