Cell Metabolism Part 2


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Cell Metabolism Part 2

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