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Enzymes dr arifullah [compatibility mode]
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Enzymes dr arifullah [compatibility mode]

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  • 1. ENZYMES Outline Definition Characteristics of enzymes Types of enzymes Factors effecting enzyme activity
  • 2. The definition & Characteristics of enzymes • A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds. a type of protein Characters: • a catalyst • Effective in smaller quantities • efficient and specific • reaction can be reversed • activities affected by surroundings • need helpers – cofactors/prostethic grps • involve in multiple steps of biochemical pathways
  • 3. Classification of enzymes  6 main classes according to International Union of Biochemistry and Molecular Biology (IUBMB): 1. oxidoreductase 2. transferase 3. hydrolase 4. lyase 5. isomerase 6. ligase
  • 4. • Function: catalyzes oxidation-reduction reactions • e.g. alcohol dehydrogenase • Other e.g. Biliverdin reductase; Glucose oxidase
  • 5. • Function: catalyzes reactions involving transfer of functional groups • e.g. Hexokinase • Other e.g. Glycoaldehyde transferase; DNA nucleotidylexotransferase
  • 6. • Function: catalyzes hydrolytic reactions involving use of water mol. • e.g. Triacylglycerol lipase • Other e.g. -amino acid esterase; Oxaloacetase H2O
  • 7. • Function: catalyzes cleavage of C-C, C-O, C- N and other bonds by other means than by hydrolysis or oxidation • e.g. Lysine decarboxylase • other e.g.: threonine aldolase [EC 4.1.2.5]; cystine lyase
  • 8. • Function: catalyzes intramolecular arrangement • e.g. Maleate isomerase • Other e.g. Inositol-3-phosphate synthase; Maltose epimerase]
  • 9. • Function: catalyzes the joining of two molecules with concomitant hydrolysis of the diphosphate bond in ATP or a similar triphosphate • e.g. Pyruvate carboxylase • Other e.g. GMP synthase; DNA ligase
  • 10. Enzyme as protein • exhibits characteristics like other proteins • primary structure  amino acid sequence e.g.: human pancreatic lipase (467 amino acids) N-Met1-…-Ser171-...-Asp194-...-His281-…-Cys467-C human trypsin (247 amino acids) N-Met1-…-His63-…-Asp107-…-Ser200-…-Ser247-C
  • 11. Lysozyme’s tertiary structure Anti-parallel -sheet (3) -helix (5)
  • 12. Aspartate carbamoyltransferase’s quartenary structure  2 catalytic trimers  3 regulatory dimers
  • 13. How enzyme reacts E + S ES E + P
  • 14. Enzyme reaction…hypothesis • lock and key hypothesis:  proposed by Emil Fischer (1894)  perfect match like specific key & lock
  • 15. • induced-fit hypothesis:  proposed by Daniel Koshland (1958)  shows elasticity/flexibility at active site  well-accepted
  • 16. e.g.: hexokinase reaction
  • 17. Factors affecting enzyme activity • enzyme concentration • substrate concentration • pH • temperature • inhibitors
  • 18. A B
  • 19. Change in pH effects the pull/push force of polar/nonpolar intramolecules which change the enzyme shape as well as active site – in acidic conditions, basic grps are protonized while in basic conditions, acidic grps are deprotonized.
  • 20. A C B
  • 21. • substances which bind to enzyme & disrupt the enzyme activity by blocking the production of ES-complex or E + P • reversible & irreversible
  • 22. • involves the noncovalent links between inhibitor and enzyme • 2 types:  competitive inhibitor  noncompetitive inhibitor  uncompetitive inhibitor Reversible inhibitors
  • 23.  competitive inhibitor  mol. similar to substrate  compete with substrate for active site e.g.: succinate dehydrogenase (E); succinate (S); malonate (I)
  • 24.  noncompetitive inhibitor  mol./ion attaches to second site (other than active site) at enzyme surface e.g.: prostaglandin synthase (E); arachidonate (S); aspirin (I)
  • 25.  uncompetitive inhibitor  binds to ES complex, forming an inactive ESI complex  e.g..: polymerase (E); nucleic acid (S); nevirapine (I) - HIV
  • 26. • covalently bonded – react with functional grp at active site, blocking active site from substrate rendering the enzyme inactive • mostly are toxic substances • e.g.: (see attached list) Irreversible inhibitors
  • 27. THANK YOUTHANK YOU