Classification of amino acids

Classification and general structure of aminiacids

1. Classification of amino acids Biochemistry for medics www.namrata.co 24-Mar-17 1 Namrata Chhabra NAMRATA CHHABRA,M.D.

2. Amino acids Provide the monomer units from which the long polypeptide chains of proteins are synthesized 24-Mar-17 2 Namrata Chhabra

3. L-amino acids and their derivatives participate in cellular functions as diverse as: Nerve transmission and the Biosynthesis of porphyrins, Purines, pyrimidines, and urea . Amino acid s 24-Mar-17 Namrata Chhabra 3

4. Short polymers of amino acids called peptides perform prominent roles in the neuroendocrine system as : hormones, hormone-releasing factors, neuromodulators, or neurotransmitters. Amino acid s 24-Mar-17 Namrata Chhabra 4

5. General structure of an amino acid Each amino acid (except proline) has a carboxyl group , an amino group and a distinctive side chain bonded to the alpha carbon atom. At physiological pH the carboxyl group is dissociated forming the negatively charged carboxylate ion(-COO - ), and the amino group is protonated(-NH 3 + ) 24-Mar-17 5 Namrata Chhabra

6. Classification of amino acids Amino acids can be classified in 4 ways: Based on structure Based on the side chain characters Based on nutritional requirements Based on metabolic fate 24-Mar-17 6 Namrata Chhabra

7. Aliphatic amino acids They are classified in three broad categories: Mono amino mono carboxylic acids They are further subdivided in 5 groups: Simple amino acids-example: glycine, alanine Branched chain amino acids-e.g.: valine,leucine,isoleucine Hydroxyl group containing amino acids-e.g.: serine, threonine Sulphur containing amino acids-e.g.: cysteine, cystine , methionine Amide group containing amino acids-e.g.- asparagine,glutamine 24-Mar-17 Namrata Chhabra 7 1) Classification based on structure

8. Mono amino dicarboxylic acid Example :aspartic acid, glutamic acid Di /poly amino mono carboxylic acid Example : lysine, arginine 2) Aromatic amino acids 3) Heterocyclic amino acids 4) Imino acids 5) Derived amino acids 1) Classification based on structure(contd.) 24-Mar-17 Namrata Chhabra 8

9. 1) Aliphatic amino acids: a) Mono-amino mono-carboxylic acids: Simple amino acids: Glycine , Alanine 24-Mar-17 9 Namrata Chhabra

10. a) Mono-amino mono-carboxylic acids (contd.) Branched chain amino acids: Valine, Leucine and Isoleucine 24-Mar-17 10 Namrata Chhabra

11. a) Mono-amino mono-carboxylic acids (contd.) - OH group-containing amino acids: Serine and Threonine 24-Mar-17 11 Namrata Chhabra

12. a) Mono-amino mono-carboxylic acids(contd.) Sulfur-containing amino acids: Cysteine, Cystine(Formed by linking of two cysteine residues) and Methionine. 24-Mar-17 12 Namrata Chhabra

13. a) Mono-amino mono-carboxylic acids (contd.) Amide group-containing amino acids: Glutamine and Asparagine 24-Mar-17 13 Namrata Chhabra

14. a) Mono-amino di-carboxylic acids Aspartic acid and Glutamic acid 24-Mar-17 14 Namrata Chhabra

15. a) Di- basic mono-carboxylic acids: Arginine and Lysine 24-Mar-17 15 Namrata Chhabra

16. ii ) Aromatic amino acids Phenyl alanine and tyrosine 24-Mar-17 16 Namrata Chhabra

17. iii) Heterocyclic Amino Aci ds: Tryptophan and Histidine 24-Mar-17 17 Namrata Chhabra

18. iv) Imino acid Proline 24-Mar-17 18 Namrata Chhabra

19. v) Derived Amino Acids: Non- α -amino acids e.g.: β -alanine, γ -amino butyric acid (GABA), δ -amino Levulinic acid Derived and Incorporated in tissue proteins : e.g.: Hydroxy-proline, hydroxy-lysine Derived but not incorporated in tissue proteins: e.g.: Ornithine, Citrulline, Homocysteine, Arginosuccinic acid 24-Mar-17 19 Namrata Chhabra

20. 2) Classification based on side chain characters Amino acids with a non-polar side-chain: e.g.: Alanine, Valine, Leucine, Isoleucine, Phenylalanine, Tryptophan, Proline Each of these amino acids has a side chain that does not bind or give off protons or participates in hydrogen or ionic bonds. Side chains of these amino acids can be thought of as “Oily” or lipid like , a property that promotes hydrophobic interactions . 24-Mar-17 20 Namrata Chhabra

21. 24-Mar-17 Namrata Chhabra 21 A) Amino acids with a non-polar side-chain:

22. B) Amino acids with a polar but uncharged side-chain: e.g. Serine, Threonine, Tyrosine, Cysteine, Asparagine and Glutamine. These amino acids are uncharged at neutral pH, although the side chains of cysteine and Tyrosine can lose a proton at an alkaline pH. Serine , Threonine and Tyrosine each contains a polar hydroxyl group that can participate in hydrogen bond formation. Side chains of Asparagine and Glutamine contain a carbonyl group and amide group, they can also participate in hydrogen bond formation. 24-Mar-17 22 Namrata Chhabra

23. 24-Mar-17 Namrata Chhabra 23 Amino acids with a polar but uncharged side-chain

24. C) Amino acids with a charged side-chain Amino acids with a positively charged side-chain: The basic amino acids- Lysine, Arginine and Histidine Amino acids with a negatively charged side-chain: The acidic amino acids- Glutamic acid and Aspartic acid They are hydrophilic in nature. 24-Mar-17 24 Namrata Chhabra

25. 24-Mar-17 Namrata Chhabra 25 Amino acids with a charged side-chain

26. 3)- Classification based on nutritional requirements Essential amino acids: These amino acids cannot be synthesized in the body and have to be present essentially in the diet. Examples- Valine, Isoleucine, Leucine, Lysine, Methionine, Threonine, Tryptophan, and Phenylalanine . 24-Mar-17 26 Namrata Chhabra

27. Semi-essential amino acids : These amino acids can be synthesized in the body but the rate of synthesis is lesser than the requirement(e.g. during growth, repair or pregnancy) Examples- Arginine and Histidine. 3)- Classification based on nutritional requirements 24-Mar-17 Namrata Chhabra 27

28. Non-essential amino acids: These amino acids are synthesized in the body, thus their absence in the diet does not adversely affect the growth. Examples- Glycine, Alanine, and the other remaining amino acids . 3)- Classification based on nutritional requirements 24-Mar-17 Namrata Chhabra 28

29. 4)-Classification based on metabolic fate The carbon skeleton of amino acids can be used either for glucose production or for the production of ketone bodies, Based on that Both glucogenic and ketogenic amino acids: Isoleucine, Tyrosine, Phenylalanine and Tryptophan 24-Mar-17 29 Namrata Chhabra

30. Purely Ketogenic amino acids: Leucine and Lysine 4)-Classification based on metabolic fate 24-Mar-17 Namrata Chhabra 30

31. Purely Glucogenic amino acids: The remaining 14 amino acids are glucogenic- Alanine, Valine Serine, Threonine, Glycine, Methionine, Cysteine, Cystine, Asparagine, Glutamine, Aspartic acid, Glutamic acid, Histidine and Arginine. 4)-Classification based on metabolic fate 24-Mar-17 Namrata Chhabra 31

32. Non standard amino acids Of the over 300 naturally occurring amino acids, 20 constitute the monomer units of proteins. These 20 amino acids are called the Primary or Standard amino acids . Selenocysteine is the 21 st Amino Acid The other are Pyroglutamate and Pyrolysine. 24-Mar-17 32 Namrata Chhabra

33. THANKS 24-Mar-17 Namrata Chhabra 33