269256 amino-acids-peptides-and-proteins

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269256 amino-acids-peptides-and-proteins

  1. 1. www.Examville.com Online practice tests, live classes, tutoring, study guides Q&A, premium content and more .
  2. 2. Amino Acids, Peptides and Proteins
  3. 3. The Proteins speak: “ We are the basis of structure and function of life; Composed of twenty amino acids, the building blocks; Organized into primary, secondary, tertiary and quaternary structure; Classified as simple, conjugated and derived proteins.”
  4. 4. <ul><li>AMINO ACIDS </li></ul><ul><li>group of organic compounds containing two functional groups: </li></ul><ul><li>amino group (-NH 2 )  basic </li></ul><ul><li>carboxyl group (-COOH)  acidic </li></ul>
  5. 5. <ul><li>General Structure of Amino Acids </li></ul><ul><li>H H </li></ul><ul><li>R C COOH R C COOH </li></ul><ul><li> NH 2 NH 3 </li></ul><ul><li>General Structure Exists as ion </li></ul>
  6. 6. <ul><li>⍺ - amino acids </li></ul><ul><li>amino </li></ul><ul><li>groups – attached to the </li></ul><ul><li>carboxyl same carbon Atom </li></ul><ul><li>⍺ - carbon atom  binds to a side chain  represented by R (different for each of the 20 amino acids found in proteins) </li></ul><ul><li>Ionized forms  how they exist </li></ul>
  7. 7. <ul><li>Classification of Amino Acids </li></ul><ul><li>based on polarity </li></ul><ul><li>of the R group </li></ul><ul><ul><ul><li>4 groups </li></ul></ul></ul><ul><ul><ul><li>Polarity  reflects the functional role of AA in protein structure </li></ul></ul></ul>
  8. 8. <ul><li>Non-polar AA </li></ul><ul><ul><ul><li>hydrophobic (water hating) </li></ul></ul></ul><ul><ul><ul><li>No charge on the ‘R’ group </li></ul></ul></ul><ul><ul><ul><li>Examples are: </li></ul></ul></ul><ul><ul><ul><li>Alanine Methionine </li></ul></ul></ul><ul><ul><ul><li>Leucine Phenylalanine </li></ul></ul></ul><ul><ul><ul><li>Isoleucine Tryptophan </li></ul></ul></ul><ul><ul><ul><li>Valine Proline </li></ul></ul></ul>
  9. 9. <ul><li>3. Polar AA with (+) ‘R’ group </li></ul><ul><ul><ul><li>carries (+) charge </li></ul></ul></ul><ul><ul><ul><li>Examples: </li></ul></ul></ul><ul><ul><ul><li>Histidine Arginine Lysine </li></ul></ul></ul><ul><li>4. Polar AA with (-) ‘R’ group </li></ul><ul><ul><ul><li>carries (-) charge </li></ul></ul></ul><ul><ul><ul><li>Examples: </li></ul></ul></ul><ul><ul><ul><li>Glutamic Acid Aspartic Acid </li></ul></ul></ul>
  10. 10. <ul><li>2. Polar AA with no charge </li></ul><ul><li>on ‘R’ group </li></ul><ul><ul><ul><li>no charge on the ‘R’ group </li></ul></ul></ul><ul><ul><ul><li>possess groups  hydroxyl </li></ul></ul></ul><ul><ul><ul><li>sulfhydryl </li></ul></ul></ul><ul><ul><ul><li>amide </li></ul></ul></ul><ul><ul><ul><li>participate in hydrogen bonding of </li></ul></ul></ul><ul><ul><ul><li>protein structure </li></ul></ul></ul><ul><ul><ul><li>Examples: </li></ul></ul></ul><ul><ul><ul><li>Asparagine Glycine Cysteine Tyrosine Serine Threonine Glutamine </li></ul></ul></ul>
  11. 11. <ul><li>Physical Properties </li></ul><ul><li>1. Solubility - soluble in water and insoluble in organic solvents </li></ul><ul><li>2. Melting Points - melt at higher temperatures often 200 °C </li></ul><ul><li>3. Taste </li></ul><ul><li>sweet (Gly, Ala, Val) </li></ul><ul><li>tasteless (Leu) </li></ul><ul><li>bitter (Arg, Ile) </li></ul><ul><li>Sodium Glutamate </li></ul><ul><li> – salt of Glutamic Acid – flavoring agent </li></ul>
  12. 12. <ul><li>4. Optical Properties </li></ul><ul><li>- Assymetric  a carbon atom is </li></ul><ul><li> attached to 4 </li></ul><ul><li> different groups </li></ul><ul><ul><ul><li>exhibiting optical isomerism </li></ul></ul></ul><ul><li>4 distinct groups R </li></ul><ul><li> H - held by an </li></ul><ul><li> COOH ⍺-carbon </li></ul><ul><li> NH 3 ໋ </li></ul>
  13. 13. <ul><li>All AA except Glycine possess optical isomers due to asymmetric ⍺-carbon atom </li></ul><ul><li>Some AA (Isoleucine, Threonine)  2 nd asymmetric carbon </li></ul>
  14. 14. <ul><li>D- and L- forms of AA based on </li></ul><ul><li>the structure of glyceraldehyde </li></ul><ul><li>CHO CHO </li></ul><ul><li>H C OH OH C H </li></ul><ul><li> CH 2 OH CH 2 OH </li></ul><ul><li> D-Glyceraldehyde L-Glyceraldehyde </li></ul>
  15. 15. <ul><li>R R </li></ul><ul><li>H C NH 2 H 2 N C H </li></ul><ul><li> COOH COOH </li></ul><ul><li> D-Amino Acid L-Amino Acid </li></ul><ul><li>The proteins are composed of L- ⍺ amino acids </li></ul>
  16. 16. <ul><li>5. Amino acids as ampholytes </li></ul><ul><ul><ul><li>can donate a proton or accept a </li></ul></ul></ul><ul><ul><ul><li>proton </li></ul></ul></ul><ul><ul><ul><li>AA contain both acidic (-COOH) and basic (-NH 2 ) groups </li></ul></ul></ul>
  17. 17. <ul><li>Zwitterion or dipolar ion: </li></ul><ul><li>Zwitter </li></ul><ul><li> from German word – means “hybrid” </li></ul><ul><li>Zwitter ion (or dipolar ion) </li></ul><ul><li> a hybrid molecule containing ( + ) and ( - ) ionic groups </li></ul>
  18. 18. <ul><li>AA rarely exist in a neutral form with free carboxylic ( - COOH) and free Amino ( - NH 2 ) groups </li></ul><ul><li>Strongly acidic pH (low pH)  AA ( + ) charged (cation) </li></ul><ul><li>Strongly alkaline pH (high pH)  AA ( - ) charged (anion) </li></ul><ul><li>Each AA has a characteristic pH (e.g. Leucine, pH – 6.0), at which it carries both ( + ) and ( - ) charges and exist as zwitterion </li></ul>
  19. 19. <ul><li>Existence of an amino acid as Cation, Anion and Zwitterion </li></ul><ul><li>H </li></ul><ul><li>H ໋ R C COOH H ໋ </li></ul><ul><li>NH 2 </li></ul><ul><li> H Amino Acid H </li></ul><ul><li>R C COOH R C COO ¯ </li></ul><ul><li> NH 3 ໋ H NH 2 </li></ul><ul><li> Cation H ໋ H ໋ Anion </li></ul><ul><li> (low pH) R C COO ¯ (high pH) </li></ul><ul><li>NH 3 ໋ </li></ul><ul><li>Zwitterion </li></ul><ul><li>(Isoelectric pH) </li></ul>
  20. 20. <ul><li>B. Chemical Properties </li></ul><ul><li>General Reactions  mostly due to the 2 functional groups </li></ul><ul><li>Reactions due to - COOH group </li></ul><ul><li>1. AA from salts (-COONa) with bases </li></ul><ul><li> and esters (-COOR’) with alcohols </li></ul><ul><li>2. Decarboxylation </li></ul><ul><li> - AA undergo decarboxylation to produce corresponding amines </li></ul>
  21. 21. <ul><li>3. Reaction with Ammonia </li></ul><ul><li>- the carboxyl group of dicarboxylic AA reacts with NH 3 to form amide </li></ul><ul><li>Asparatic Acid + NH 3  Asparagine </li></ul><ul><li>Glutamic Acid + NH 3  Glutamine </li></ul>
  22. 22. <ul><li>Reactions due to -NH 2 group </li></ul><ul><li>4. The Amino groups behave as bases and </li></ul><ul><li> combine with acids (e.g. HCl) to form </li></ul><ul><li> salts (-NH 3 + Cl ¯) </li></ul><ul><li>5. Reaction with NINHYDRIN </li></ul><ul><li>- the ⍺-AMINO ACIDS react with Ninhydrin to form a purple, blue or pink colour complex (Ruhemann’s purple) </li></ul>
  23. 23. <ul><li>Amino acid + Ninhydrin  Keto acid + NH 3 + CO 2 + Hydrindantin </li></ul><ul><li>Hydrindantin + NH 3 + Ninhydrin  Ruhemman’s purple </li></ul><ul><li>Ninhydrin reaction – quantitative determination of AA and proteins </li></ul>
  24. 24. <ul><li>6. Colour reactions of Amino Acids </li></ul><ul><li>- AA can be identified by specific colour reactions </li></ul><ul><li>Color Reactions of proteins / AA </li></ul><ul><li>Reaction Specific group or AA </li></ul><ul><li>Buiret Reaction Two peptide linkages </li></ul><ul><li>Ninhydrin Reaction ⍺ -Amino acids </li></ul><ul><li>Xanthoproteic Reaction Benzene ring of aromatic AA (Phe, Tyr, Trp) </li></ul><ul><li>Million’s reaction Phenolic Group (Tyr) </li></ul><ul><li>Hopkins – Cole Reaction Indole Ring (Trp) </li></ul>
  25. 25. <ul><li>6. Sakaguchi Reaction Guanidino Group (Arg) </li></ul><ul><li>7. Nitroprusside Reaction Sulfhydryl groups (Cys) </li></ul><ul><li>8. Paulys’ test Imidazole ring (His) </li></ul><ul><li>9. Sulfur test Sulfhydryl groups (Cys) </li></ul><ul><li>10. Folin – Coicalteau’s Phenolic groups </li></ul><ul><li>test (Tyr) </li></ul>
  26. 26. <ul><li>7. Transamination </li></ul><ul><li>- important reaction in AA metabolism </li></ul><ul><li>- transfer of an amino group from an amino acid to a keto acid to form a new AA </li></ul><ul><li>8. Oxidative deamination </li></ul><ul><li>- AA undergo oxidative deamination to liberate free ammonia </li></ul>
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