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Cell Metabolism Part 2
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  • 1. Enzymes (If you don’t have the energy, we can help!) www.freelivedoctor.com
  • 2. Enzymes
    • Biological catalysts
    • Made primarily from proteins
    • Bind to substrate
    • Not used up
    • Speed up reaction
    www.freelivedoctor.com
  • 3. Catalysis Uncatalyzed G time R P Transition E A time R P G Catalyzed www.freelivedoctor.com
  • 4. Catalysts
    • Increase rate of reaction
    • Provide activation energy
      • Energy is conserved
      • Activation energy has to come from somewhere
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  • 5. Sources of Activation energy
    • Binding energy
      • Solvent released from active site when substrate binds increases Δ S surr
    • Induced fit
      • Enzyme forces substrate into unstable transition state
      • Catalytic antibodies
    • Binding substrate brings reactive groups together
    www.freelivedoctor.com
  • 6. Catalysis by an enzyme
    • E + S  > ES  > EP  > E + P
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  • 7. Enzyme Example Serine Proteases
    • Active site and substrate
      • Note side chain interactions
      • Substrate diffuses into active site
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  • 8. Serine proteases
    • Substrate binds to active site
    • Chemical groups interact
    • Force substrate into unstable intermediate
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  • 9. Serine Proteases
    • Peptide bond is cleaved
    • Serine in active site is bound to carboxyl side of peptide
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  • 10. Serine proteases
    • Half of protein diffuses out
    • Enzyme used up
      • Has to be regenerated
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  • 11. Serine proteases
    • Water diffuses into active site
    • Juxtaposes chemical groups
      • Similar reaction to first
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  • 12. Serine proteases
    • New unstable intermediate generated
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  • 13. Serine Proteases
    • Carboxyl end of peptide diffuses out
    • Enzyme regenerated
    • Ready for another round
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  • 14. Serine protease summary
    • Enzyme stabilized by various side chain interactions
    • Substrate binds to enzyme.
      • Fits pocket
      • Forms unstable intermediate
      • Chemical groups on enzyme do reaction
    • Chemistry happens and product diffuses out
    • Enzyme regenerated
    www.freelivedoctor.com
  • 15. Kinetics
    • Study of reaction rates
    • Why?
      • Used to determine mechanisms
    • Michaelis Menton kinetics
      • V = rate of reaction
        • V max = maximum reaction rate
      • [S]
        • Substrate concentration
        • Km = substrate concentration where rate is half maximal
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  • 16. Michaelis-Menton Plot www.freelivedoctor.com
  • 17. Enzyme inhibition, Competitive
    • Both substrate and inhibitor bind to active site
      • Compete
    • Inhibitor blocks substrate from binding
    www.freelivedoctor.com E S I E I S
  • 18. Michaelis- Menton Plot for competitive inhibition uninhib V max V max /2 K m inhibited K mi V [S] www.freelivedoctor.com
  • 19. Michaelis- Menton Plot for competitive inhibition
    • V max is not changed
    • K m increased
      • Since substrate has to outcompete the inhibitor for the active site, it takes more substrate to get to the same rate.
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  • 20. Noncompetitive Inhibition
    • Inhibitor binds to an allosteric site on the enzyme
    • Changes active site so substrate doesn’t bind
    S I I www.freelivedoctor.com
  • 21. Michaelis- Menton Plot for noncompetitive inhibition uninhib V max /2 K m V max uninhib V max inhib V [S] www.freelivedoctor.com
  • 22. Michaelis- Menton Plot for noncompetitive inhibition
    • Inhibition lowers V max
    • K m unchanged
      • Since inhibitor doesn’t bind to active site, changing amount of substrate will have no effect
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  • 23. Michaelis Menton Kinetics Summary
    • Competitive inhibition
      • Inhibitor competes with substrate for active site
        • V max unchanged
        • K m increased
    • Noncompetitive inhibition
      • Inhibitor binds to allosteric site changing active site
        • V max lowered
        • K m unchanged
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  • 24. Allosteric Activation
    • Active site will not bind substrate
    • Allosteric activator binds and changes shape of active site
    • Now substrate binds
    S A A S www.freelivedoctor.com