Structure & Properties Of 20 Standard Amino Acids

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All proteins are macromolecules because of their very high molecular weights. These are the polymers, i.e., chain-like molecules produced by joining a number of small units of amino acids called monomers. The amino acids are, therefore, regarded as ‘building blocks of proteins. 

Each amino acid is a nitrogenous compound having both an acidic carboxyl (— COOH) and a basic amino (— NH2) group. R stands for the side chains that are different for each amino acid. R can be as simple as a hydrogen atom (H) or a methyl group (— CH3) or a more complex structure. The first carbon is the part of the carboxyl group. The second carbon, to which is attached the amino group, is called the α-carbon. The α-carbon of most amino acids is joined by covalent bonds to 4 different groups. Thus, the α-carbon in all the amino acids is asymmetric except in glycine where the α-carbon is symmetric.

Structure of 20 standard amino acids

1. Alanine – ala – A

Alanine - ala - A

2. Arginine – arg – R

Arginine - arg - R

3. Asparagine – asn – N

Asparagine - asn - N

4. Aspartic acid – asp – D

Aspartic acid - asp - D

5. Cysteine – cys – C

Cysteine - cys - C

6. Glutamine – gln – Q

Glutamine - gln - Q

7. Glutamic acid – glu – E

Glutamic acid - glu - E

8. Glycine – gly – G

Glycine - gly - G

9. Histidine – his – H

Histidine - his - H

10. Isoleucine – ile – I

Isoleucine - ile - I

11. Leucine – leu – L

Leucine - leu - L

12. Lysine – lys – K

Lysine - lys - K

13. Methionine – met – M

Methionine - met - M

14. Phenylalanine – phe – F

Phenylalanine - phe - F

15. Proline – pro – P

Proline - pro - P

16. Serine – ser – S

Serine - ser - S

17. Threonine – thr – T

Threonine - thr - T

18. Tryptophan – trp – W

Tryptophan - trp - W

19. Tyrosine – tyr – Y

Tyrosine - tyr - Y

20. Valine – val – V

Valine - val - V

Twenty Amino acids can be grouped according to the characteristics of the side chains as follows:

Aliphatic – alanine, glycine, isoleucine, leucine, proline, valine.
Aromatic – phenylalanine, tryptophan, tyrosine.
Acidic – aspartic acid, glutamic acid.
Basic – arginine, histidine, lysine.
Hydroxylic – serine, threonine.
Sulphur-containing – cysteine, methionine.
Amidic (containing amide group) – asparagine, glutamine.

Properties of 20 standard amino acids

Properties of common amino acids