1. In the TCA cycle, carbon enters the cycle as ____ and exits as ____ with metabolic
energy captured as ____, ____ and ____.
D. acetylCoA? CO2? ATP? NADH? [FADH2]
2. In eukaryotic cells, glycolysis occurs in the ____, and the TCA cycle reactions take place
in ____.
B. cytoplasm? mitochondria
3. The ____ of pyruvate to acetylCoA is catalyzed by ____.
B. decarboxylation? pyruvate dehydrogenase complex
4. The pyruvate dehydrogenase complex contains three multimeric enzymes (ETA, EPDH, and
EDLD). All are properties of EPDH EXCEPT:
C. It binds NAD+ in its active site.
5. The following statements are correct about the reaction catalyzed by the pyruvate
dehydrogenase complex EXCEPT:
C. NAD+ is the direct oxidant of reduced lipoamide.
6. Order the coenzymes according to their involvement in the pyruvate dehydrogenase
complex.
A.
NAD+
CoASH
TPP
Lipoate (lipoamide)
[FAD]
B.
C.
D.
E.
C. C, D, B, E, A
7. All are correct statements about the reaction catalyzed by citrate synthase EXCEPT:
A. Citrate synthase is allosterically activated by ATP.
8. Citrate synthase has a ____ DG� and is essentially ____ even though the mitochondrial
concentration of ____ is very low.
D. large negative? irreversible? OAA
9. Citrate synthase is a ____ with binding of ____ inducing a conformational change ____
the binding of acetylCoA, and ____ is an allosteric inhibitor.
A. dimer? OAA? increasing? NADH
10. Which is NOT true of citrate synthase?
B. it is not regulated
11. Citrate must be isomerized to isocitrate because the ____ group of citrate is not
oxidizable, but the ____ group of isocitrate can be oxidized.
B. tertiary alcohol? secondary alcohol
12. ____ catalyzes citrate isomerization to isocitrate by abstracting ____ from citrate to
yield [____], then ____ in the opposite position to produce isocitrate.
C. Aconitase? water? aconitate? rehydration
13. All are true for aconitase EXCEPT:
E. all are true.
14. Fluoroacetate inhibits the TCA cycle. Although it does not inhibit citrate synthase, the
product inhibits:
A. aconitase.
15. Which enzymes of the TCA cycle catalyze oxidative decarboxylation reactions?
D. isocitrate dehydrogenase and aketoglutarate dehydrogenase
16. The two step reaction catalyzed by isocitrate dehydrogenase involves:
bdecarboxylation expelling the aketo carboxyl as CO2.
oxidation of the C2 alcohol of isocitrate to form oxalosuccinate.
oxidation of the C2 alcohol to form oxaloacetate.
beliminatio
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
18. Isocitrate dehydrogenase has all of the characteristics EXCEPT:
A. ADP raises the Km for isocitrate by a factor of 10.
19. aKetoglutarate dehydrogenase is a multienzyme complex analogous to:
D. pyruvate dehydrogenase.
20. The coenzymes listed below are associated with aketoglutarate dehydrogenase complex
EXCEPT:
E. biotin.
21. The only reaction of the citric acid cycle that provides substratelevel phosphorylation is
catalyzed by:
D. succinylCoA synthetase.
22. All are characteristics of succinylCoA synthetase EXCEPT:
E. all of the above are true.
23. The correct sequence of steps between succinylCoA and ATP in mammals to
"preserve" the energy of the thioester bond are:
A.
B.
C.
D.
succinylphosphate.
phosphohistidine.
GTP.
AcetylCoA.
A. A, B, C
24. Characteristics of succinate dehydrogenase include all EXCEPT:
D. it removes hydrogens from CO bonds.
25. The succinate dehydrogenase mechanism involves the ____ of succinate, which is
exergonic and can be used to provide for the ____.
C. oxidation? reduction of [FAD]
26. The succinate dehydrogenase catalyzed reaction involves dehydrogenation ____ to a
carbonyl group and is ____ to yield a ____ double bond.
C. a,b? stereospecific? trans
27. The correct sequence of electron transport in the succinate dehydrogenase reaction
mechanism is:
A.
B.
C.
D.
Coenzyme Q (UQ).
[FAD].
ironsulfur clusters.
electron transport chain.
C. B, C, A, D
28. Fumarase catalyzes a reaction for which each of the following is true EXCEPT:
E. all are true
29. Characteristics of the oxidation of malate to oxaloacetate (OAA) include all EXCEPT:
C. is very exergonic.
30. The oxidation of malate to oxaloacetate is not thermodynamically favored under
standard conditions. It occurs because:
D. oxaloacetate is used in the next reaction, which has a negative DG.
31. How many NADH molecules are produced in the TCA cycle per molecule of acetyl
CoA oxidized?
C. 3
32. Which of the following represents a reaction that could be used to refill the CAC?:
D. pyruvate � OAA
33. The anaplerotic reactions associated with the TCA cycle are a result of the:
A. use of many of the TCA cycle intermediates in biosynthesis.
34. When acetylCoA levels exceed the ____ supply, allosteric activation of ____ by ____
raises the oxaloacetate (OAA) levels for condensation with acetylCoA to form ____.
D. OAA? pyruvate carboxylase? acetylCoA? citrate
35. All are true for pyruvate carboxylase EXCEPT:
B. in mitochondria of plants, but not animals.
36. The reaction CO2 + PEP + GDP � OAA + GTP is catalyzed by:
B. PEP carboxykinase.
37. The three reactions of the citric acid cycle with large negative DG values include:
A.
B.
C.
D.
E.
F.
G.
H.
citrate synthase.
aconitase.
isocitrate dehydrogenase.
aketoglutarate dehydrogenase.
succinylCoA synthetase.
succinylCoA dehydrogenase.
fumaras
B. A, C, D
38. All are principal allosteric regulatory "signals" controlling the TCA cycle activity
EXCEPT:
E. all are true.
39. It is crucial that regulation occur at pyruvate dehydrogenase because:
C. the product acetylCoA is committed to oxidation in the citric acid cycle or fatty acid
biosynthesis.
40. Mammalian pyruvate dehydrogenase is regulated by phosphorylation using the enzyme
____ which is allosterically activated by high levels of ____ and ____.
D. pyruvate dehydrogenase kinase? NADH? acetylCoA
41. In mammalian tissues, isocitrate dehydrogenase is allosterically stimulated by:
A. high NAD+/NADH and high ADP/ATP ratios.
42. Inhibition of the citric acid cycle at isocitrate dehydrogenase increases the levels of
citrate and isocitrate that may increase the production of:
C. glyoxylate and cytosolic acetylCoA.
43. All of the following are inhibitors of citrate synthase EXCEPT:
A. acetylCoA
44. An essential feature of the glyoxylate cycle, which is not associated with the TCA cycle
is:
A. it utilizes condensation of acetylCoA with succinate.
45. All are true statements for the glyoxylate pathway EXCEPT:
C. glyoxysomes contain all of the enzymes for the glyoxylate cycle.
46. The isocitrate lyase catalyzed reaction cleaves isocitrate into:
D. succinate and glyoxylate.