Biochemistry Test 6

187 Questions | Total Attempts: 187

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Biochemistry Exam Quizzes & Trivia

Biochemistry II


Questions and Answers
  • 1. 
     In the TCA cycle, carbon enters the cycle as ____ and exits as ____ with metabolic energy captured as ____, ____ and ____. 
    • A. 

      Acetyl-CoA; CO2; ATP; NADH; [FADH2]

    • B. 

      Malonyl-CoA; water; NADH; [FADH2]; ATP

    • C. 

       succinyl-CoA; CO2; ATP; NADH; NADPH

    • D. 

       acetyl-CoA; CO2; NADH; ATP; NADPH

    • E. 

      Malonate; water; NADH; ATP; NADPH


  • 2. 
     In eukaryotic cells, glycolysis occurs in the ____, and the TCA cycle reactions take place in ____. 
    • A. 

      Mitochondria; mitochondria

    • B. 

      Cytoplasm; mitochondria

    • C. 

      Cytoplasm; cytoplasm


    • D. 

      Mitochondria; ribosomes


    • E. 

      Cytoplasm; ribosomes

  • 3. 
    The ____ of pyruvate to acetyl-CoA is catalyzed by ____. 
    • A. 

      Dehydration; pyruvate dehydration complex

    • B. 

      Decarboxylation; pyruvate dehydrogenase complex

    • C. 

      Decarboxylation; pyruvate decarboxylase

    • D. 

      Transacylation; pyruvate transacylase


    • E. 

       none of the above.

  • 4. 
    The pyruvate dehydrogenase complex contains three multimeric enzymes (ETA, EPDH, and EDLD). All are properties of EPDH EXCEPT: 
    • A. 

      It uses thiamin pyrophosphate as a catalytic coenzyme.

    • B. 

      It oxidatively decarboxylates pyruvate.

    • C. 

      It binds NAD+ in its active site.

    • D. 

      It transfers an acetyl group to lipoamide of ETA.

    • E. 

      It forms a hydroxyethyl-TPP intermediate.

  • 5. 
    The following statements are correct about the reaction catalyzed by the pyruvate dehydrogenase complex EXCEPT: 
    • A. 

       it is the link between glycolysis and the TCA cycle

    • B. 

      The activity of the complex is regulated by the phosphorylation of EPDH.

    • C. 

      NAD+ is the direct oxidant of reduced lipoamide.

    • D. 

      An FAD is covalently linked to the EDLD, the lipoamide dehydrogenase component.

    • E. 

      Although EPDH is called "pyruvate dehydrogenase" it is not a dehydrogenase.

  • 6. 
    Order the coenzymes according to their involvement in the pyruvate dehydrogenase complex.
    • A. 

      A, B, C, D, E 

    • B. 

       C, B, A, E, D

    • C. 

      C, D, B, E, A

    • D. 

      B, D, E, A, C

    • E. 

      C, E, D, B, A

  • 7. 
    All are correct statements about the reaction catalyzed by citrate synthase EXCEPT: 
    • A. 

      Citrate synthase is allosterically activated by ATP.

    • B. 

      The complete chemical equation is: Oxaloacetate + acetyl-CoA + H2O -> citrate + CoA

    • C. 

      Citryl-CoA is formed as an intermediate.

    • D. 

      The mechanism involves attack of the carbanion of acetyl-CoA on the carbonyl carbon of oxaloacetate.

    • E. 

      The enzyme uses general base catalysis to generate the reactive species.

  • 8. 
    Citrate synthase has a ____ DG¢ and is essentially ____ due to the ____ of the CoA thioester. 
    • A. 

      Large positive; reversible; oxidation

    • B. 

      Nearly zero; reversible; reduction

    • C. 

      Nearly zero; irreversible; reduction

    • D. 

       large negative; irreversible; hydrolysis

    • E. 

      Large negative; reversible; hydrolysis

  • 9. 
    Citrate synthase is a ____ with binding of ____ inducing a conformational change ____ the binding of acetyl-CoA, and ____ is an allosteric inhibitor. 
    • A. 

      Dimer; OAA; increasing; NADH

    • B. 

      Dimer; OAA; decreasing; NADH

    • C. 

      Tetramer; OAA; decreasing; NAD+

    • D. 

      Monomer; pyruvate; decreasing; ATP

    • E. 

      Monomer; pyruvate; increasing; ATP

  • 10. 
     Which is NOT true of citrate synthase? 
    • A. 

      It catalyzes the first reaction in the TCA cycle

    • B. 

      It is not regulated

    • C. 

      OAA and acetyl-CoA bind to the active sites

    • D. 

      The citrate synthase reaction liberates a relatively large amount of energy

    • E. 

      All of the above are true

  • 11. 
    Citrate must be isomerized to isocitrate because the ____ group of citrate is not oxidizable, but the ____ group of isocitrate can be oxidized. 
    • A. 

      Ketone; primary alcohol

    • B. 

      Tertiary alcohol; secondary alcohol

    • C. 

      Ketone; secondary alcohol

    • D. 

      Aldehyde; primary alcohol

    • E. 

      Secondary alcohol; ketone

  • 12. 
    ____ catalyzes citrate isomerization to isocitrate by abstracting ____ from citrate to yield the enzyme-bound intermediate ____, followed by ____ to produce isocitrate. 
    • A. 

      Citrate isomerase; CO2; trans-aconitate; carboxylation

    • B. 

      Citrate isomerase; water; trans-aconitate; rehydration

    • C. 

      Aconitase; water; cis-aconitate; rehydration

    • D. 

      Aconitase; CO2; cis-aconitate; carboxylation

    • E. 

      None are true

  • 13. 
    All are true for aconitase EXCEPT: 
    • A. 

      Iron atom acts as a Lewis acid.

    • B. 

      Equilibrium favors citrate.

    • C. 

      Contains an iron-sulfur cluster.

    • D. 

      One Fe3+ coordinates with C-3 carbonyl and hydroxyl group of citrate.

    • E. 

      All are true.

  • 14. 
    Fluoroacetate is a potent inhibitor of the TCA cycle. Which step of the TCA cycle is inhibited as a result of fluoroacetate entering the TCA cycle? 
    • A. 

      Citrate synthase

    • B. 

      Aconitase

    • C. 

      Isocitrate dehydrogenase

    • D. 

      A-ketoglutarate dehydrogenase

    • E. 

      Succinyl-CoA synthetase

  • 15. 
    Which enzymes of the TCA cycle catalyze oxidative decarboxylation reactions? 
    • A. 

       malate dehydrogenase and citrate synthase


    • B. 

      Fumarase and succinate dehydrogenase

    • C. 

      A-ketoglutarate dehydrogenase and succinate dehydrogenase


    • D. 

      Isocitrate dehydrogenase and a-ketoglutarate dehydrogenase


    • E. 

       aconitase and succinate dehydrogenase

  • 16. 
    The two step reaction catalyzed by isocitrate dehydrogenase involves:
    • A. 

      A and B

    • B. 

      B and C

    • C. 

      C and D

    • D. 

      A and C

    • E. 

      B and D

  • 17. 
    Allosteric inhibitors of isocitrate dehydrogenase include ____ and ____, whereas ____ acts as an allosteric activator, ____ the Km for isocitrate. 
    • A. 

      ATP; NADH; ADP; lowering

    • B. 

      ATP; ADP; AMP; lowering


    • C. 

       NADH; NADPH; AMP; increasing


    • D. 

      NADH; ATP; ADP; increasing

    • E. 

      NADH; ATP; AMP; lowering

  • 18. 
    Isocitrate dehydrogenase has all of the characteristics EXCEPT:
    • A. 

      ADP raises the Km for isocitrate by a factor of 10.

    • B. 

      Virtually inactive in the absence of ADP.


    • C. 

      Sufficiently exergonic to pull the aconitase reaction forward.


    • D. 

      Allosterically inhibited by NADH and ATP.


    • E. 

      An oxidative-decarboxylation reaction.

  • 19. 
    A-Ketoglutarate dehydrogenase is a multi-enzyme complex analogous to: 
    • A. 

       pyruvate kinase.

    • B. 

      Glyceraldehyde-3-phosphate dehydrogenase.


    • C. 

       isocitrate dehydrogenase.

    • D. 

      Pyruvate dehydrogenase.

    • E. 

      Lactate dehydrogenase.

  • 20. 
    The coenzymes listed below are associated with a-ketoglutarate dehydrogenase complex EXCEPT: 
    • A. 

       [FAD].

    • B. 

      TPP.

    • C. 

      Lipoamide.

    • D. 

      NAD+.

    • E. 

      Biotin.

  • 21. 
    The only reaction of the citric acid cycle that provides substrate-level phosphorylation is catalyzed by: 
    • A. 

       malate dehydrogenase.

    • B. 

      Citrate synthase.


    • C. 

      Isocitrate dehydrogenase.

    • D. 

      Succinyl-CoA synthetase.

    • E. 

      Nucleotide triphosphate kinase.

  • 22. 
    All are characteristics of succinyl-CoA synthetase EXCEPT: 
    • A. 

      Succinyl-CoA can be used to drive phosphorylation of GDP or ADP.


    • B. 

      The enzyme is named for the reverse reaction.


    • C. 

       it provides an example of substrate-level phosphorylation.

    • D. 

      Succinyl-phosphate is an intermediate in the reaction catalyzed by succinyl-CoA synthetase.

    • E. 

      All of the above are true.

  • 23. 
    The correct sequence of steps between succinyl-CoA and ATP in mammals to "preserve" the energy of the thioester bond are:
    • A. 

      A, B, C

    • B. 

      B, C, A

    • C. 

      A, C, D

    • D. 

      C, B, A

    • E. 

      D, A, B

  • 24. 
    Characteristics of succinate dehydrogenase include all EXCEPT: 
    • A. 

      It is also known as succinate-Coenzyme Q reductase.

    • B. 

      It has covalently bound FAD.

    • C. 

      It is a membrane-bound enzyme.

    • D. 

      It removes hydrogens from C-O bonds.

    • E. 

       it carries out either 1-electron or 2-electron transfers to/from FAD.

  • 25. 
    The succinate dehydrogenase mechanism involves the ____ of succinate, which is exergonic and can be used to provide for the ____. 
    • A. 

      Oxidation; reduction of NAD+

    • B. 

      Reduction; oxidation of NAD+

    • C. 

      Oxidation; reduction of [FAD]

    • D. 

      Reduction; oxidation of [FAD]

    • E. 

      None are true