BCH 361 Exam 1 Ch 6

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BCH 361 Exam 1 Ch 6
2014-02-17 18:38:41


ch 6
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  1. Properties of Enzymes
    A catalyst enhances the rate of reaction by decreasing the activation energy for a reaction
  2. Oxidoreductases
    catalyze redox reactions
  3. Transferases
    transfer a group from one molecule to another
  4. Hydrolases
    cleave bonds by adding water
  5. Lyases
    catalyze removal of groups to form double bonds or the reverse
  6. Isomerases
    catalyze intramolecular rearrangements
  7. Ligases
    bond two molecules together
  8. Chymotrypsin. At low substrate concentrations, the reaction is ___ order in substrate. As the concentration of substrate increases, the order changes and approaches ___. Thus the graph is ___.
    • 1st
    • 0
    • hyperbolic
  9. Aspartate transcarbamoylase (ATCase) leads to the synthesis of ___.
    • nucleobases
    • sigmoidal
  10. The plots for cymotrypsin and aspartate transcarbamoylase should remind us of the oxygen bindingcurves for myoglobin and hemoglobin respectively. Thus, cymotrypsin is ___ and ATCase is an ___ enzyme.
    • nonallosteric
    • allosteric
  11. Michaelis-Menten Kinetics explains the behavior of ___ enzymes. It assumes an ___ complex is formed.
    • nonallosteric
    • enzyme-substrate
  12. non-allosteric:
    At low substrate concentrations, the reaction is ___ order with respect to substrate.
  13. non-allosteric: At high substrate concentrations, the enzyme is saturated with substrate. The order is ___ and a ___
    • zero
    • Vmax
  14. The lower the Km, the ___ the affinity for complex formation.
  15. kcat = Vmax/[Et]
    turnover #
  16. km = [S] at the ___ point
    1/2 Vmax

  17. determine y=mx+b
    • y = 1/v 
    • m = Km / Vmax
    • x = 1/S
    • b = 1/Vmax
  18. competitive inhibitor looks structurally like the ___and binds to the enzyme at the ___.
    • substrate 
    • active site
  19. An uncompetitive inhibitor binds to the ___ complex.
    • enzyme-substrate
    • or other than active site
  20. For competitive inhibitor, Vmax ___, slope ___ and Km ___.
    • constant
    • increases
    • increases
  21. Noncompetitive Inhibitor, Vmax ___ slope ___ and Km ___.
    • lowered
    • increases
    • constant
  22. Proximity and Strain Effects
    Substrate closely approaches the catalytic site with proper orientation
  23. Electrostatic Effects
    A hydrophobic pocket in the enzyme lowers the surrounding dielectric constant allowing electrostatic interaction between E and S.
  24. Acid-Base catalysis
    Enzyme side chains act as proton donors and acceptors
  25. Covalent Catalysis
    A nucleophilic side chain forms an unstable covalent bond to the substrate.
  26. Cofactors: Metals
    Transition metals are useful because they
    • Have a high positive charge density.
    • Act as Lewis acids (accepte pairs). Or neucleophile
    • Can mediate redox reactions
    • Help polarize water molecules
  27. Nicotinic acid (niacin) is involved in ___ reactions.
  28. The active site on Chymotrypsin (CT) involves the ___.
    • serine 195 residue
    • histidine 57 residue
  29. for Chymotrypsin, The histidine acts as a ___ catalyst, converting the serine to its ___ and making it a better ___ for attack at the carbonyl carbon to be hydroylzed.
    • general base
    • anion
    • nucleophile
  30. methods that organisms use to regulate enzyme activity are:
    • Genetic control
    • Covalent modification
    • Allosteric regulation
    • Compartmentation
  31. Genetic control --> 
    • enzyme induction
    • e.coli uses lactose in the absence of glucose
  32. covalent modification
    • phosphorylation and dephosphorylation
    • Glycogen phosphorylation, methylation and acetylation
  33. zymogens?
    inactive enzyme precursor that requires a biochemical change to become an active enzyme
  34. Allosteric Regulation
    Pacemaker (regulatory) enzymes usually catalyze the “committed” step in a series of biochemical reactions or a step where branching to two paths can occur.
  35. Compartmentation
    Eukaryotic cells are divided into organelles which often allows for separation of opposing processes