BIOC 384 EXAM 4 UPDATED ACTUAL QUESTIONS AND
CORRECT ANSWERS
Question:
1. How would an increased level of acetyl-CoA be
expected to affect the pyruvate dehydrogenase
reaction?
Answer:
The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in
an inhibition of pyruvate dehydrogenase activity.
Question:
2. If acetyl-CoA is not metabolized by the citrate cycle, its
most likely metabolic fate is
Answer:
is used to synthesize fatty acids.
Question:
3. How is the pyruvate dehydrogenase enzyme regulated?
Answer:
covalent modification
Question:
4. Calculate the ΔE°' of a coupled redox reaction with O2
and ferredoxin (Fe2+) using the table below.
Answer:
+1.25V
Question:
5. Calculate the ΔG°' of a redox reaction of pyruvate and
hydrogen under standard conditions using the table
below.
Answer:
36.66 kJ/mol
Question:
6. Why is the ΔG°' of the condensation of oxaloacetate and
acetyl-CoA highly favorable?
Answer:
The hydrolysis of the thioester bond in citryl-CoA results in the highly exergonic
reaction.
,Question:
7. In two turns of the citrate cycle, how many electrons are
transferred from the citrate cycle intermediates to NAD+
and FAD?
Answer:
16
Question:
8. Which molecules function as electron acceptors in the
citrate cycle?
Answer:
NAD+, FAD
Question:
9. Regeneration of NAD+ and FAD inside the mitochondrial
matrix is required because
Answer:
they maintain flux through the citrate cycle.
Question:
10. Identify the strongest oxidant (a) and strongest reductant
(b) in the table below.
Answer:
a) O2 b) ferredoxin
Question:
11. When the citrate cycle is inhibited, which two metabolites
are exported to the cytosol for fatty acid and cholesterol
synthesis?
Answer:
citrate and malate
Question:
12. In the citrate cycle, a high concentration of NADH would
result in
Answer:
inhibition of α-ketoglutarate dehydrogenase
, Question:
13. Complex III has a critical role in the electron transport
system as a major redox center.
a) Calculate the standard free energy change in Complex
III when comparing CoQ oxidation and Cyt C reduction.
b) Assuming 100% efficiency in oxidative phosphorylation,
how many ATP equivalents would this account for?
Explain.
Answer:
a) -33 kJ/mol
b) ~1 ATP equivalent because standard change in free energy of ATP hydrolysis is
~-30 kJ/mol.
Question:
14. Use the table below to answer the question.
In the direction indicated, which of the following
reactions are thermodynamically favored?
I. NAD+ + H2O --> O2 + NADH
II. FADH2 + H2O --> O2 + FAD
III. NADH + O2 --> H2O + NAD+
Answer:
III only
Question:
15. Identify the correct order of electron transfers in the
electron transport chain starting from FADH2.
Answer:
complex II --> complex III --> cytochrome c --> complex IV
Question:
16. The regulatory mechanism in the citrate cycle involving
the NADH to NAD+ ratio is considered to be an example
of regulation by
Answer:
product inhibition.
Question:
17. What would happen to the electron transport system
(ETS) and oxidative phosphorylation pathway in the
presence of excess NADH if the mitochondrial matrix
were not closed, but opened up to the cytoplasm?
Answer:
The ETS complexes would function as normal, but no ATP would be made.
CORRECT ANSWERS
Question:
1. How would an increased level of acetyl-CoA be
expected to affect the pyruvate dehydrogenase
reaction?
Answer:
The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in
an inhibition of pyruvate dehydrogenase activity.
Question:
2. If acetyl-CoA is not metabolized by the citrate cycle, its
most likely metabolic fate is
Answer:
is used to synthesize fatty acids.
Question:
3. How is the pyruvate dehydrogenase enzyme regulated?
Answer:
covalent modification
Question:
4. Calculate the ΔE°' of a coupled redox reaction with O2
and ferredoxin (Fe2+) using the table below.
Answer:
+1.25V
Question:
5. Calculate the ΔG°' of a redox reaction of pyruvate and
hydrogen under standard conditions using the table
below.
Answer:
36.66 kJ/mol
Question:
6. Why is the ΔG°' of the condensation of oxaloacetate and
acetyl-CoA highly favorable?
Answer:
The hydrolysis of the thioester bond in citryl-CoA results in the highly exergonic
reaction.
,Question:
7. In two turns of the citrate cycle, how many electrons are
transferred from the citrate cycle intermediates to NAD+
and FAD?
Answer:
16
Question:
8. Which molecules function as electron acceptors in the
citrate cycle?
Answer:
NAD+, FAD
Question:
9. Regeneration of NAD+ and FAD inside the mitochondrial
matrix is required because
Answer:
they maintain flux through the citrate cycle.
Question:
10. Identify the strongest oxidant (a) and strongest reductant
(b) in the table below.
Answer:
a) O2 b) ferredoxin
Question:
11. When the citrate cycle is inhibited, which two metabolites
are exported to the cytosol for fatty acid and cholesterol
synthesis?
Answer:
citrate and malate
Question:
12. In the citrate cycle, a high concentration of NADH would
result in
Answer:
inhibition of α-ketoglutarate dehydrogenase
, Question:
13. Complex III has a critical role in the electron transport
system as a major redox center.
a) Calculate the standard free energy change in Complex
III when comparing CoQ oxidation and Cyt C reduction.
b) Assuming 100% efficiency in oxidative phosphorylation,
how many ATP equivalents would this account for?
Explain.
Answer:
a) -33 kJ/mol
b) ~1 ATP equivalent because standard change in free energy of ATP hydrolysis is
~-30 kJ/mol.
Question:
14. Use the table below to answer the question.
In the direction indicated, which of the following
reactions are thermodynamically favored?
I. NAD+ + H2O --> O2 + NADH
II. FADH2 + H2O --> O2 + FAD
III. NADH + O2 --> H2O + NAD+
Answer:
III only
Question:
15. Identify the correct order of electron transfers in the
electron transport chain starting from FADH2.
Answer:
complex II --> complex III --> cytochrome c --> complex IV
Question:
16. The regulatory mechanism in the citrate cycle involving
the NADH to NAD+ ratio is considered to be an example
of regulation by
Answer:
product inhibition.
Question:
17. What would happen to the electron transport system
(ETS) and oxidative phosphorylation pathway in the
presence of excess NADH if the mitochondrial matrix
were not closed, but opened up to the cytoplasm?
Answer:
The ETS complexes would function as normal, but no ATP would be made.
