Toughest Biochemistry Quiz Exam!

187 Questions | Total Attempts: 287

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Toughest Biochemistry Quiz Exam!

Can you pass the toughest biochemistry quiz? The body of biochemical knowledge we have collected in the last fifty years has allowed an enormous revolution in the medical field. Physics and chemistry control the way reactions and activities work in nature. Biochemistry takes the knowledge from chemistry to study the essential processes that make up biology. This biochemistry quiz is a bit difficult, but you can do it with a little focus and motivation.


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

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