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PROTEINS

PROTEINS. Polymer of amino acids linked by amide linkage. Functions: Nutritional: growth, digestion, metabolism (enzymes). Physical structure: cheese, bread, foaming agent, gel-forming. O. O. C H. C OH. HO C H. NH. C H. 2.

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PROTEINS

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  1. PROTEINS • Polymer of amino acids linked by amide linkage. • Functions: • Nutritional: growth, digestion, metabolism (enzymes). • Physical structure: cheese, bread, foaming agent, gel-forming.

  2. O O C H C OH HO C H NH C H 2 CH OH CH 2 3 Amino Acids L -Glyceraldehyde L - Alanine Zwitterion O O - C O C OH + NH C H NH C H 2 3 CH CH 3 3

  3. Evidence of Zwitterion in Amino Acids at Neutral pH

  4. L is naturally-occurring form for amino acids. Ionizable groups Zwitterion pKa for pKb for What form do we get at pH = 1? pH = 3.5? pH = 7.5? pH =9.5? and pH = 11.5?

  5. DISSOCIATION OF THE CARBOXYL GROUP (pKa)

  6. DISSOCIATION OF THE AMINO GROUP (pKb)

  7. RELATIONSHPI BETWEEN DISSOCIATION OF THE AMINO GROUP (pKb) AND pH [A-] pH = pK + Log [AH] [COO-] [NH2] pH - pK = Log or Log [COOH] [NH3+]

  8. Effects of pH on the Concentration of Different Groups pKb = 9.5 Log [NH2] [COO-] [NH3+] [COOH] pH 11.5 9.3 2 pKa = 2.2 Log pH 1 -1.2 -8.5 pH 2.2 0 -7.3 pH 3.5 1.3 -6 pH 5.5 3.3 -3.3 pH 7.5 5.3 -3 pH 9.5 7.3 0

  9. pK'1 a - COO- pK'2 a - NH3+ pK'R R Group pI Glycine 2.34 9.78 6.06 Alanine 2.35 9.69 6.02 Isoleucine 2.36 9.69 6.02 Serine 2.21 9.15 5.68 Aspartic Acid 2.09 9.82 3.86 2.97 Asparagine 2.02 8.80 5.41 Glutamic Acid 2.19 9.67 4.25 3.22 Glutamine 2.17 9.13 5.65 Histidine 1.82 9.17 6.00 7.58 Cysteine 1.71 10.78 8.33 5.02 Tyrosine 2.20 9.11 10.07 5.65 Arginine 2.17 9.04 12.48 10.76 Lysine 2.18 8.95 10.53 9.74 pK' AND pI VALUES OF CERTAIN AMINO ACIDS

  10. GROUPS OF AMINO ACIDS 1. Aliphatic amino acids 2. Hydroxy amino acids 3. Acidic amino acids 4. Amide amino acids 5. Basic amino acids 6. Sulfur-containing amino acids 7. Aromatic amino acids 8. Secondary amino acids

  11. Aliphatic Amino Acids Glycine (GLY) (a - amino ethanoate) Alanine (ALA) (a - amino propionate)

  12. Aliphatic Amino Acids Valine (VAL) (a - amino isovalerate) Leucine (LEU) (a - amino isocaproate)

  13. Aliphatic Amino Acids Isoleucine (ILE) (a - amino b - methyl-valerate)

  14. Amino Acids with Alcohol Serine (SER) (a - amino b - hydroxy propionate) Threonine (THR) (a - amino b - hydroxy butyrate)

  15. Amino Acids with additional Acidic Group Aspartic Acid (ASP) (a - amino succinate) Glutamic Acid (GLU) (a - amino glutarate)

  16. Amino Acids with Amides of Acidic Amino Acids Asparagine (ASN) (a - amino b - succinamide) Glutamine (GLN) (a - amino g - glutaramide)

  17. Basic Amino Acids Lysine (LYS) (a, e - diamino caproate) Arginine (ARG) (a - amino d - guanidine valerate)

  18. Basic Amino Acids Histidine (HIS) (a - amino b - imidazole propionate)

  19. Sulfur-containing Amino Acids Cysteine (CYS H) (a - amino b - mercapto propionate) Cystine (CYS-CYS) Di(a - amino b - mercapto propionate)

  20. Sulfur-containing Amino Acids Methionine (MET) (a - amino g - methyl mercapto butyrate)

  21. Aromatic Amino Acids Phenylalanine (PHE) (a - amino b - phenyl propionate) Tyrosine (TYR) (a - amino b - [p - hydroxyphenyl])

  22. Aromatic Amino Acids Tryptophan (TRY) (a - amino b - indol propionate)

  23. Secondary Amino Acids Proline (PRO) (2- carboxy pyrollidine) Hydroxyproline (HYPRO) (2- carboxy-4-hydroxy-pyrollidine)

  24. AMIDE LINKAGE - Some double-bond character

  25. Amide Linkage and Peptides AMIDE LINKAGE - Some double-bond character

  26. PROTEIN STRUCTURE Primary Structure: due to covalent peptide bonds of amino acids. Primary structure of a polypeptide chain showing the N- and C- terminal amino acids.

  27. Secondary Structure of Protein

  28. Primary Structure of Protein

  29. Primary Structure of Protein

  30. Primary Structure of Protein

  31. Secondary Structure: due to hydrogen bonding between peptide bond. Small negative charged oxygen atom = d- Small positive charged hydrogen atom = d+ Kinds of Secondary Structure: 1. a - Helix 2. Pleated sheets structure A. Parallel B. Anti-parallel

  32. a - Helix

  33. Secondary structure

  34. Secondary Structure of Protein

  35. Secondary Structure of Protein

  36. Secondary Structure of Protein

  37. Secondary Structure of Protein

  38. Secondary Structure

  39. Tertiary Structure: aggregation of individual protein. 1. Hydrophobic attraction: the close association attraction of hydrocarbon side-chains. 2. Ionic bond: between positively charged groups and negatively charged groups. 3. Hydrogen bonds 4. Disulfide bonds A protein has size and shape as well as unique arrangement through hydrogen, ionic, hydrophobic and disulfide bonds.

  40. Different Chemical Bonds in Tertiary Structure

  41. Tertiary Structure of Protein

  42. Secondary Structure of Protein

  43. Tertiary Structure of Protein

  44. Tertiary Structure of Protein

  45. QUATERNARY STRUCTURE A protein has size and shape as well as unique arrangement of its polypeptide chains. (Aggregation of several peptide chains to form a definite molecule by ionic bond, hydrogen bond, and/or hydrophobic bond).

  46. Quaternary Structure of Protein

  47. Quaternary Structure of Protein

  48. Quaternary Structure of Protein

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