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. Keep reading to get the comprehensive list of the structure and properties of 20 standard amino acids.

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.

Read more about Biological Catalysts – Enzymes

Structure of 20 standard amino acids

1. Alanine – ala – A

2. Arginine – arg – R

3. Asparagine – asn – N

4. Aspartic acid – asp – D

5. Cysteine – cys – C

6. Glutamine – gln – Q

7. Glutamic acid – glu – E

8. Glycine – gly – G

9. Histidine – his – H

10. Isoleucine – ile – I

11. Leucine – leu – L

12. Lysine – lys – K

13. Methionine – met – M

14. Phenylalanine – phe – F

15. Proline – pro – P

16. Serine – ser – S

17. Threonine – thr – T

18. Tryptophan – trp – W

19. Tyrosine – tyr – Y

20. 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

Frequently Asked Questions

What are amino acids?

Amino acids are the building blocks of proteins that are made up of an amino group and a carboxylic group. Both these groups along with a hydrogen atom and a side chain are attached to a central carbon atom.

How amino acids are classified?

Amino acids are classified based on the properties of the side chain -R. The properties of the functional groups or atoms present in the side chain determine the properties of amino acids.

What are 5 polar amino acids?

The polar amino acids include aspartate, glutamate, asparagine, glutamine, and histidine. 

What are acidic amino acids?

Amino acids having a carboxylic group in their side chain -R, are called acidic amino acids. These include aspartate and glutamate.