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Classification of amino acids


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Classification and general structure of aminiacids

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Classification of amino acids

  1. 1. Biochemistry for medics 3/25/2017 1Namrata Chhabra NAMRATA CHHABRA,M.D.
  2. 2. Provide the monomer units from which the long polypeptide chains of proteins are synthesized 3/25/2017 2Namrata Chhabra
  3. 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. 3/25/2017Namrata Chhabra 3
  4. 4.  Short polymers of amino acids called peptides perform prominent roles in the neuroendocrine system as :  hormones,  hormone-releasing factors,  neuromodulators, or  neurotransmitters. 3/25/2017Namrata Chhabra 4
  5. 5.  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(-NH3 +) 3/25/2017 5Namrata Chhabra
  6. 6. Amino acids can be classified in 4 ways: 1.Based on structure 2.Based on the side chain characters 3.Based on nutritional requirements 4.Based on metabolic fate 3/25/2017 6Namrata Chhabra
  7. 7. 1) Aliphatic amino acids They are classified in three broad categories:  Mono amino mono carboxylic acids They are further subdivided in 5 groups: a. Simple amino acids-example: glycine, alanine b. Branched chain amino acids-e.g.: valine,leucine,isoleucine c. Hydroxyl group containing amino acids-e.g.: serine, threonine d. Sulphur containing amino acids-e.g.: cysteine, cystine, methionine e. Amide group containing amino acids-e.g.- asparagine,glutamine 3/25/2017Namrata Chhabra 7
  8. 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 3/25/2017Namrata Chhabra 8
  9. 9.  Simple amino acids: Glycine , Alanine 3/25/2017 9Namrata Chhabra
  10. 10.  Branched chain amino acids: Valine, Leucine and Isoleucine 3/25/2017 10Namrata Chhabra
  11. 11. -OH group-containing amino acids: Serine and Threonine 3/25/2017 11Namrata Chhabra
  12. 12. Sulfur-containing amino acids: Cysteine, Cystine(Formed by linking of two cysteine residues) and Methionine. 3/25/2017 12Namrata Chhabra
  13. 13. Amide group-containing amino acids: Glutamine and Asparagine 3/25/2017 13Namrata Chhabra
  14. 14. Aspartic acid and Glutamic acid 3/25/2017 14Namrata Chhabra
  15. 15. Arginine and Lysine 3/25/2017 15Namrata Chhabra
  16. 16. Phenyl alanine and tyrosine 3/25/2017 16Namrata Chhabra
  17. 17. Tryptophan and Histidine 3/25/2017 17Namrata Chhabra
  18. 18. Proline 3/25/2017 18Namrata Chhabra
  19. 19.  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 3/25/2017 19Namrata Chhabra
  20. 20. A. 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. 3/25/2017 20Namrata Chhabra
  21. 21. 3/25/2017Namrata Chhabra 21
  22. 22. 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. 3/25/2017 22Namrata Chhabra
  23. 23. 3/25/2017Namrata Chhabra 23
  24. 24. a) Amino acids with a positively charged side-chain: The basic amino acids- Lysine, Arginine and Histidine b) Amino acids with a negatively charged side-chain: The acidic amino acids- Glutamic acid and Aspartic acid They are hydrophilic in nature. 3/25/2017 24Namrata Chhabra
  25. 25. 3/25/2017Namrata Chhabra 25
  26. 26. I. 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. 3/25/2017 26Namrata Chhabra
  27. 27. II. 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. 3/25/2017Namrata Chhabra 27
  28. 28. III. 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. 3/25/2017Namrata Chhabra 28
  29. 29. The carbon skeleton of amino acids can be used either for glucose production or for the production of ketone bodies, Based on that I.Both glucogenic and ketogenic amino acids:  Isoleucine,  Tyrosine,  Phenylalanine and  Tryptophan 3/25/2017 29Namrata Chhabra
  30. 30. II. Purely Ketogenic amino acids:  Leucine and  Lysine 3/25/2017Namrata Chhabra 30
  31. 31. II. 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. 3/25/2017Namrata Chhabra 31
  32. 32. 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 21st Amino Acid The other are Pyroglutamate and Pyrolysine. 3/25/2017 32Namrata Chhabra
  33. 33. 3/25/2017Namrata Chhabra 33