Amino acid

amino acid

1. By Sridarshini Chandra AMINO ACID

2. CONTENTS Introduction Classification of amino acid Physical properties of amino acids Chemical properties of amino acids Functions of amino acids

3. What is amino acid? Amino acids are the molecules having one amino group , one carboxyl group , one H atom and one specific group ( R group ) attached to the central C atom. R group varies in structure, size , electric charge and influence the solubility of amino acid in water. The key elements of amino acids are C,N,O,H. Amino acids are basic structural building blocks of protein.

4. Basic structure of amino acid

5. Classification of amino acid According to the structure of side chain According to polarity of the side chain (R group) According to the nutritional requirements According to the metabolic fate

6. Amino acids with aliphatic side chains Name of Amino acid Structure of the amino acid Special group present Symbol ( 3 letters ) Symbol ( 1 letter) Glycine Hydrogen atom Gly G Alanine Methyl group Ala A Valine Isopropyl group Val V Leucine Isobutyl group Leu L Isoleucine Sec-butyl group IIe I

7. Amino acids containing Hydroxyl(-OH) group Name of amino acid Structure of amino acid Special group present Symbol (3 letter) Symbol (1 letter) Serine Hydroxymethyl group Ser S Threonine 1-Hydroxyethyl group Thr T Tyrosine 4-Hydroxybenzyl group Tyr Y

8. Amino acids containing Sulfur Name of amino acid Structure of amino acid Special group present Symbol (3 letter) Symbol (1 letter) Cysteine Sulfhydryl Cys C Cystine Disulfide _ _ Methionine Thioether Met M

9. Acidic Amino acids and their derivatives Name of amino acid Structure of amino acid Special group present Symbol (3 letter) Symbol (1 letter) Aspartic acid 2-Carboxyl group Asp D Asparagine Amide Asn N Glutamic acid 3-carboxyl group Glu E Glutamate amaide Gln Q

10. Basic amino acids and their derivatives Name of amino acid Structure of amino acid Special group present Symbol (3 letter) Symbol (1 letter) Lysine amino Lys K Arginine Guanidino Arg R Histidine Imidazole His H

11. Aromatic amino acids Name of amino acid Structure of amino acid Special group present Symbol (3 letter) Symbol (1 letter) Phenylalanine Benzylyl group Phe F Tyrosine 4-hydroxybenzyl group Tyr Y tryptophan Indole Trp W

12. Imino Acid Name of amino acid Structure of amino acid Special group present Symbol (3 letter) Symbol (1 letter) Proline Pyrrolidine Pro P

13. Nutritional classification of amino acid Essential or indispensable amino acid Non-essential or dispensable amino acid amino acid

14. Essential amino acid Essential amino acids are not synthesized by the body. Need to be supplied through diet. Required for proper growth and maintainance of individual. Arginine,Valine,Histidine,Isoleucine,Leucine , Lysine, Methionine, Threonine , Tryptophan, Phenylalanine

15. Semi-essential amino acid Arginine and Histidine can be synthesized by adults but not by growing children, hence these are considered as semi-essential amino acids.

16. Non-essential amino acid These can be synthesized by the body to meet the biological needs. need not to be consumed through the diet. Glycine, Alanine, Serine, Cysteine , Aspartate, Asparagine , Glutamate, Glutamine, Proline, Tyrosine.

17. Classification of amino acid based on polarity Non-Polar, aliphatic amino acid Aromatic amino acid Polar uncharged( R group) amino acid Polar positively charged amino acid Polar negatively charged amino acid

18. Non-polar, aliphatic amino acid These are Hydrophobic amino acids . Glycine Alanine Valine Leucine Isoleucine Methionine Proline

19. Aromatic amino acid Contains aromatic side chain. Less hydrophobic as compared to aliphatic non-polar amino acids. Phenylalanine, Tyrosine, Tryptophan . Tyrosine and tryptophan are more polar than phenylalanine because of the hydroxyl group of tryosine and the nitrogen atom of tryptophan.

20. Polar, uncharged R group amino acids Hydrophilic in nature . Contains functional groups that form hydrogen bond with water. Serine Threonine Cysteine Asparagine Glutamine

21. Polar, charged (R group) Amino acids Polar positively charged amino acids More hydrophilic as compared to non-polar amino acids and polar uncharged amino acids. These are basic in nature. Lysine Arginine Histidine Polar negatively charged Amino acids More hydrophilic as compared to non-polar amino acids and polar uncharged amino acids. These are acidic in nature. Aspartate glutamate

22. Classification of amino acid according to metabolic fate Both Glycogenic and Ketogenic amino acid: Isoleucine , Tyrosine, Phenylalanine, Tryptophan Purely Ketogenic amino acids : Leucine , Lysine Purely Glycogenic amino acids : Alanine , Valine , Serine, Threonine , Glycine , Methionine , Asparagine , Glutamine, Cysteine , Cystine , Aspartic acid, Glutamic acid, Histidine , Arginine .

23. Non- standard amino acid In addition to 20 common amino acids proteins may contain residues created by modification of the common residues already incorporated into polypeptide chain. eg . 4-Hydroxyproline 5-Hydroxylysine 6-N-Methyllysine

24. Desmosine Derivative of four lysine residues

25. Selenocysteine It is present during protein synthesis rather than created through post synthetic modification of amino acid residues. Known as 21 st amino acid.

26. Amino acids as AMPHOLYTES: Amino acids contain both acidic group (-COOH) and basic (-NH 2 ) group. They can donate or accept a proton and hence known as ampholytes.

27. In strongly acidic pH amino acid is positively charged. In strongly alkaline pH amino acid is negatively charged.

28. Isoelectric pH Isoelectric pH may be defined as a pH at which a molecule exist as a zwitter ion or dipolar ion and carries no net charge . Molecule is electrically neutral at isoelectric pH.

29. Isoelectric point 7/5/2012 29 Biochemistry For Medics

30. Physical properties of amino acids Solubility : most of the amino acids are soluble in water but insoluble in organic solvents. Melting point: Amino acids generally melt at high temperature , often above 200 c. Taste: Amino acids may be sweet( Gly , Ala, Val); tasteless ( Arg , Ile); Monosodium glutamate(MSG ; ajinamoto ) is used as flavoring agent in food industry. In some individuals intolerant to MSG Chinese restaurant syndrome (flu like) is observed.

31. Stereochemistry of Amino acids All AMINO ACIDS ARE OPTICALLY ACTIVE(EXCEPT GLYCINE ) All amino acids ( except Glycine ) have one asymmetrical carbon or chiral carbon , to which four different groups are attached(carboxyl group, amino group, hydrogen atom, R group) The mirror images of a molecule of amino acid are non- superimposable to each other. Amino acids do not have plane of symmetry.

32. Nonsuperimposable mirror image of Amino acid

33. All amino acids rotate the plane of polarized light . These are nonsuperimposable mirror image of each other and known as Enantiomer of each other. If the carboxyl group is written at the top , the D form refers to the isomer having –NH 2 at on the right; the L form refers to the amino acid having -NH 2 group on the left.

34. Reactions of amino acids Reactions due to amino group. Reactions due to carboxyl group. Reactions due to side chain. Reaction due to both amino and carboxyl groups.

35. Reactions due to both amino & carboxyl groups Formation of peptide bond 7/5/2012 Biochemistry For Medics

36. Functions of amino acids Provide the monomer units from which the long polypeptide chain of proteins are synthesized . (Condensation of two molecules of amino acids forms a peptide bond ) L-amino acids and their derivatives participate in cellular functions as diverse as nerve transmission and the biosynthesis of porphyrins , purines , pyrimidines , and urea . Short polymers of amino acids called poly peptide perform prominent roles in the neuroendocrine system as hormones, hormone-releasing factors, neurotransmitters

37. Functions of amino acids Niacin, Serotonin and melatonin are synthesized from Tryptophan Melanin, thyroid hormone, catecholamines are synthesized from Tyrosine GABA (neurotransmitter) is synthesized from Glutamic acid Nitric oxide , a smooth muscle relaxant is synthesized from Arginine . Act as precursors for haem , creatine , Porphyrins , purines and pyrimidines .

38. Reference Principle of Biochemistry Albert L. Lehninger, David L. Nelson, Michael M.Cox 6 th edition,chapter-3,amino acid and protein, page no- 75-85. Biochemistry, U.Satyanarayana, U.Chakrapani 3rd edition, chapter- 3, proteins and amino acids , page no-43-57 Outlines of Biochemistry, Eric E. Conn & P.K.Stumpf 3 rd edition, chapter3,amino acid and proteins ,page no-55-67 Harper’s Illustrated Biochemistry, Murry,Bender,Botham,Kennelly,Rodwell,Weil, 28 th edition, amino acids, page no-14-25.

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