Lec 7 - Amino acids bio-chemistry - Copy.pptx

Amino acids

1. Lec 7: Amino acids – Classification, structure and properties (amphoteric nature, isomerism, Zwitter ion, colour reactions), essential amino acids.

2. What are Amino acids “ The fundamental building block of proteins is amino acids” Also called as fundamental structural unit of all proteins. There are 2 functional groups present in the amino acids (except proline) Amino group : NH 2 Carboxyl group : COOH All proteins are formed from 20 different amino acids .

3. General structure of amino acid

4. Amino acid 1 and Amino acid 2 are linked by peptide bond

5. What are protein amino acids and non-protein amino acids? 20 amino acids found in proteins - standard or normal or protein amino acids . There are many other amino acids found in nature but do not occur in protein- non-protein amino acids .

6. How amino acids are named Different amino acids are named depending on where they are first isolated or based upon their properties. Asparagine was named so, as it was isolated from asparagus. G lycine was so named because of its sweet taste (Greek:' glykos ' meaning sweet).

7. Classification based on nutrition

8. Physical properties of amino acid Amino acids are white crystalline substances . Most of them are soluble in water and insoluble in non-polar organic solvents (e.g., chloroform and ether). Aliphatic and aromatic amino acids particularly those having several carbon atoms have limited solubility in water but readily soluble in polar organic solvents. They have high melting points varying from 200-300 o C or even more. They are tasteless, sweet or bitter. Some are having good flavour . Sodium glutamate is a valuable flavouring agent and is used in the preparation of certain dishes and sauces.  

9. Amphoteric nature of amino acids Amino acids are amphoteric compounds, as they contain both acidic (COOH) and basic (NH 2 ) groups. They can react with both alkalies and acids to form salts. In acid solution amino acids carry positive charges and hence they move towards cathode in an electric field. In alkaline solution , the amino acids carry negative charges and therefore move towards anode.

10. Amphoteric nature of amino acid

11. Zwitter ion When an amino acid is dissolved in water, it exists as inner salt carrying both positive and negative charges. The amino acids possessing both positive and negative charges are called zwitterions.

12. Zwitter ion

13. Low pH – Amino acid has Net positive charge High pH – Amino acid has Net negative charge. These reactions are reversible. I soelectric pH or isoelectric point – Amino acid has net charge of zero pH at which the amino acid has no tendency to move either towards positive or negative electrode .

14. Isomerism S tructure of amino acids reveals that except glycine , all other amino acids possess asymmetric carbon . P resence of asymmetric carbon atom, amino acids exist in optically active forms . L-forms are more common than D-forms . M ost of the naturally occurring amino acids are L-amino acids.

15. L and D refers to steric configuration not optical rotation The direction of optical rotation of amino acid is indicated by the symbol + or -, which follows the designation 'D' or 'L'.

16. Colour reactions of proteins and aminoacids Ruhemann’s purple formed. Amino acid undergoes degradation Yellow colour formed . When NaOH added it turns orange Aromatic amino acids in the protein react with concentrated nitric acid to form yellow nitro derivatives.

17. 3) Violet ring is formed at the junction Indole group of tryptophan reacts glyoxylic acid. 4) Violet colour is formed Compounds having two or more peptide bonds gives a violet colour with alkaline copper sulphate

18. 5) Appearance of red colour Pauly’s diazo test makes the use of chemical reagent ( sulphanilic acid) which goes through diazotation reaction (amino acids couple with the diazonium salt) 6) Appearance of red colour Millon’s test is based upon the nitration reaction (amino acid reacts with concentrated nitric acid)  

19. Differences between Essential & Non-essential amino acids ESSENTIAL AMINO ACIDS NON-ESSENTIAL AMINO ACIDS Cannot be synthesized by the human body and other vertebrates Can be synthesized by the body from the essential amino acids It should be supplied through diet. Need not to be supplied through diet. There are 10 essential amino acids There are 12 non-essential amino acids They include P henylalanine, V aline, T hreonine, T rptophan , I soleucine, M ethionine, H istidine, A rginine, L eucine & L ycine . They include G lycine, G lutamate, G lutamine, A sparagine, A spartate, A lanine, P roline, C ysteine, T yrosine and S erine. Code word: (PVT TIM HALL) Code word: (G3, A3, PCTS)