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Quiz #4/5

Quiz #4/5. Quiz #4/5. #4: Glycolysis (Tuesday, Feb 20 th ) #5: TCA cycle (Monday, Mar 5 th ) Pathways are in the books Quiz will have the entire pathway: All cofactors will be present Random intermediate and enzymes removed You fill in the missing names

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Quiz #4/5

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  1. Quiz #4/5

  2. Quiz #4/5 • #4: Glycolysis (Tuesday, Feb 20th) • #5: TCA cycle (Monday, Mar 5th) • Pathways are in the books • Quiz will have the entire pathway: • All cofactors will be present • Random intermediate and enzymes removed • You fill in the missing names • Draw the structure for 1 intermediate • Indicated by a larger box

  3. Enzyme Regulation

  4. Conditions Affecting Enzyme ActivitypHtemperature

  5. pH

  6. Effects of pH on Enzyme Activity • Protonation state of side chains • Variation in protein structure • Substrate binding • catalysis • Ionization of substrate • Substrate binding

  7. Temperature Protein unfolding

  8. Control of Enzyme Availability Principles of Genetic Regulation

  9. Types of Enzymes“Control of Gene Expression” • Constitutive Enzymes: e.g. glycolytic enzymes and gluconeogenic enzymes • Inducible Enzymes: e.g. b-galactosidase • Repressible Enzymes: e.g. ten enzymes of histidine biosynthesis

  10. Negative Regulators[Bind to operators or upstream repression sequences (URS)]

  11. Positive Regulators[Bind to promoters, enhancers or upstream activation sequences (UAS)]

  12. Regulation of Enzyme Catalytic Activity Covalent Modification Allosteric Enzymes

  13. Principles Governing Controls of Enzyme Catalytic Activity • Regulatory Enzymes • Enzyme catalyzing committed, rate-limiting step (often first step) • Thermodynamically highly favorable reaction • Outcomes of Regulation • Feedback inhibition (fbi) of biosynthetic pathways • Modulation of metabolic flux

  14. Reversible Covalent Modification

  15. Protein Modification(Phosphorylation/Dephosphorylation) Page 390

  16. Non-covalent Modification Effectors or Ligands Positive: activators Negative: inhibitors

  17. Allosteric Enzymes(Modulation of Enzyme Catalytic Activity) • Substrate Binding • Catalytic Rate • Both

  18. Allosteric (Regulatory) Enzymes

  19. Homotropic Effects

  20. Heterotropic Effects

  21. Glycogen Phosphorylase Figure 12-16

  22. Regulation of Biosynthetic Pathways

  23. Rationale for Regulation Efficiency and Flexibility

  24. Biological Efficiency • Biosynthesis • Synthesize precursors not available in diet • Cease synthesis when precursors become available in diet (pre-existing enzymes) • Produce precursors and macromolecules at appropriate rates • Catabolism • Degrade most appropriate nutrients at appropriate rates

  25. Biological Flexibility • Adaptaton to Dietary Changes • Need for biosynthetic products • Catabolism of new nutrients • Control of pre-existing enzymes • Metabolic Flux • Rates of metabolism reflecting needs for energy and macromolecular synthesis

  26. Competing Reactions: Regulation

  27. Control Mechanisms • Control of Enzyme Availability • Induction/repression • Control of Enzyme Activity • Covalent/Non-covalent • Control of Substrate Availability

  28. Types of Regulation • Specific: pathway’s substrate or product • General: needs for C or N sources or growth rates (e.g. energy charge)

  29. Signals Mediating Regulation Availability of Substrates or Products (Ligands) Regulatory Proteins

  30. Biosynthetic Pathways

  31. Simple Feedback Inhibition

  32. Complex Feedback Inhibition

  33. Mechanisms of Complex Feedback Inhibition • Cumulative: sum of individual inhibitions • Concerted: both end products required for inhibition • Isoenzyme: two enzymes, each inhibitable by different end product

  34. Cumulative Feedback Inhibition D E D D E E A A B B C C A B C F F G G F G

  35. Concerted Feedback Inhibition D E D D E E A A B B C C A B C F F G G F G

  36. Isozymes D E D E A B C A B C F G F G D E A B C F G

  37. Modulation of Metabolic Flux Energy Charge

  38. Energy Charge(Daniel Atkinson) Steady-State E.C. = 0.93 ATP, ADP and AMP = Regulatory Ligands

  39. Energy Charge Anabolic pathways (Biosynthesis) Catabolic Pathways (Degradation) Produce ATP Activated Low EC (AMP) Inhibited Hig EC (ATP) • Require ATP • Activated • High EC (ATP) • Inhibited • Low EC (AMP)

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