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Amino Acids – Types, Classification, Genetic Code and Applications
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Amino acids, the tiny building blocks of proteins occupies a prominent position among all the other nutrients and are reported as the molecule of source of life in theories discussing the mysteries behind origin of life. There are 20 naturally occurring amino acids and Asparagine was the first discovered amino acid in the year 1806 followed by Cysteine, Leucine and Glycine. All the 20 amino acids involved in the construction of proteins were identified in the year 1935 and this discovery marked phenomenol significance in understanding the proteins, its structure and functions. Amino acid, as the name implies has amine (-NH2) group and carboxylic acid (-COOH) with additional functional R group which acts as a side chain. Thus amino acids possess molecules of carbon, nitrogen oxygen and hydrogen. The R group alone varies from one amino acid to the other thus contributing to 20 different natural amino acids.

Types
The 20 amino acids involved in the construction of proteins are Glycine, Valine, Leucine, Isoleucine, Arginine, Cysteine, Lysine, Proline, Threonine, Methionine, Histidine, Tyrosine, Serine, Alanine, Phenylalanine, Glutamine, Glutamate, Asparagine, Aspartic acid and Tryptophan. These 20 amino acids based on their mode of availability are divided into essential (dietary intake) and non essential amino acids (synthesized in the body through metabolic process). Out of the 20 amino acids, Glycine, Arginine, Cysteine, Proline, Tyrosine, Alanine, Glutamine, Glutamate, Arginine, Asparagine and Aspartic acid are the amino acids synthesized in the body and hence falls under the category non-essential amino acids and the rest 9 amino acids are essential that is to be supplemented through diet.

Classification
Based on the type of functional group (R group) present amino acids are classified as aliphatic, aromatic, acidic, basic, acid amide, sulfur and cyclic amino acids. Based on the characteristic of the functional group amino acids are classified as polar and non-polar amino acids. They are also classified as alpha, beta, gamma and delta amino acids based on the site of attachment of the functional group.

Genetic Code
The base sequences of DNA ( A- Adenine, G-Guanine, C-Cytosine, T-Thymine) are information centers which are copied to RNA (A-Adenine, G-Guanine, C-Cytosine, U-Uracil) through transcription and the resulting RNA with complementary base sequences to that of the DNA translates the information into proteins. The sequence of bases in the RNA dictates the type of amino acid to be synthesized and as a rule three bases codes for one aminoacid and such set of three bases is called as codon. Except for the amino acids Methionine and Tryptophan all the other amino acids are represented by more than one codon and such condition is termed as degeneracy and the different set of codons representing the same amino acid are called as Synonyms. Below are the natural amino acids and the codons specific for each amino acid.

Glycine - GGU,GGC, GGA,GGG
Valine -GUU,GUC,GUA,GUG
Leucine -CUU,CUC,CUA,CUG,UUA,UUG
Isoleucine -AUU, AUC, AUA
Arginine -CGU,CGC,CGA,CGG,AGA,AGG
Cysteine-UGU,UGC
Lysine-AAA,AAG
Proline-CCU,CCC,CCA,CCG
Threonine-ACU,ACC,ACA,ACG
Methionine-AUG
Histidine-CAU,CAC
Tyrosine-UAU,UAC
Serine-UCU,UCC,UCA,UCG,AGU,AGC
Alanine-GCU,GCC,GCA,GCG
Phenylalanine -UUU,UUC
Glutamine-CAA, CAG
Glutamate-GAA, GAG
Asparagine-AAU, AAC
Aspartic acid-GAU, GAC and
Tryptophan-UGG

Apart from these codons coding specific amino acid there are three codons which do not code for any amino acid but acts as stop signal in the protein synthesis are called as Stop codons and they are UAG, UGA and UAA. The codon AUG which codes for Methionine is also called as Start codon for it initiates the protein synthesis.

Various researches carried out in order to explore the amino acid present in different food types states the correlation between the type of amino acid present in the food and the taste of the food. For example Glutamate and Aspartic acid contribute to the sour taste of the food, Glycine, Alanine, Threonine, Proline, Serine and Glutamine are sweet factors in the food and Bitter taste of the food is contributed by Phenylalanine, Tyrosine, Arginine, Leucine, Isoleucine, Valine, Histidine and Methionine.

Applications
Amino acids are used in the preparation of feed for animals. The chelating property of the amino acid makes it a suitable element enhancing the absorption of minerals from the food by the animals. Various amino acids are used in the food industry as a flavor enhancer and also used in pharmaceuticals and cosmetic preparations. The chelating nature of the amino acids when used along with fertilizers enhances the absorption of minerals from the soil by the cultivated crops. With all these applications amino acids are on its way into the synthesis of biodegradable polymers.
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Amino Acids – Types, Classification, Genetic Code and Applications - by priyasaravanan_1406 - 01-23-2013, 12:12 AM
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