Practice Questions Set 7
1. Review the reactions in glycolysis (do not memorize the reactions). Mark the “energy
investment phase” and “energy payoff/harvest phase” of glycolysis on the diagram.
Where is ATP used? Where is ATP produced? Where is NADH produced?
2. The molecule that functions as the reducing agent (electron donor) in a redox or oxidationreduction reaction
A) gains electrons and gains energy.
B) loses electrons and loses energy.
C) gains electrons and loses energy.
D) loses electrons and gains energy.
Review the principle of Redox.
3. Explain how oxidation of methane is carried out through relative loss of electrons (see figure
from textbook). 8-2 p163 Memorize this ﬁgure
4. Where in the cell does each of the following take place? Glycolysis, Pyruvate Oxidation,
Citric Acid Cycle, Electron Transport / Oxidative Phosphorylation?
5. Which process in eukaryotic cells will proceed normally whether oxygen (O2) is present or
A) electron transport
C) the citric acid cycle
D) oxidative phosphorylation
6. Explain your answer to the previous question.
7. The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mole and the free
energy for the reduction of NAD+ to NADH is +53 kcal/mole. Why are only two molecules
of NADH formed during glycolysis when it appears that as many as a dozen could be
Consider what comes out of the reaction as a net product. Where is the rest of the potential
8. Review the structure of pyruvate. Pyruvate has to enter the mitochondria in order to enter the
citric acid cycle. Will pyruvate cross the lipid bilayer membrane easily? Explain.
Is pyruvate hydrophilic or hydrophobic? Will it cross the lipid bilayer with its hydrophobic
interior made of fatty acid tails? Or will it need the help of a transport protein (regardless of
whether it’s active or passive transport)?
9. Consider the cotransport proteins involved in bringing Pyruvate into the matrix of the
mitochondria. In the absence of oxygen, why won’t pyruvate enter the mitochondria?
Consider the proton gradient across the inner membrane, and the role of oxygen in establishing
Refer to the figure below to answer the following questions.
The figure below illustrates some of the steps (reactions) of glycolysis in their proper sequence.
Each step is lettered. Use these letters to answer the questions.
10. In which step is an inorganic phosphate added to the reactant?
Look for the addition of the phosphate group indicated as a P inside a circle.
11. In addition to ATP, what are the end products of glycolysis?
Consider what comes out of the reaction as a net product.
12. Review Figure 8.8 in the textbook. Mark the energy investment and energy harvest steps.
13. Review Figure 8.8 in the textbook. Explain why step 6 is a redox reaction.
14. Review Figure 8.8 in the textbook. Explain why steps 7 and 10 are considered substratelevel phosphorylation.
What provides the phosphate for synthesis of ATP from ADP?
15. Review the citric acid cycle. How many carbon atoms are fed into the citric acid cycle as a
result of the oxidation of one molecule of glucose?
16. In the diagram of the citric acid cycle, circle and identify the step that shows substrate-level
What provides the phosphate for synthesis of ATP from ADP?
17. Review the citric acid cycle. Explain why step 6 is a redox reaction.
Gaining or losing hydrogens (not just electrons)…
18. Review the citric acid cycle. Explain why step 8 is a redox reaction.
What happens to the hydroxyl group? To NAD+?
19. Review the citric acid cycle. Explain what happens if you add an inhibitor that inhibits
20. Review the figure detailing electron transport in mitochondria. Where are iron/sulfur
proteins found in mitochondria?
21. Review the figures detailing the experiments in support of chemiosmosis. What is the big
question being asked? What are the two alternative hypotheses? The experimental
predictions? What is the control treatment?
22. What would you do using the system used by Racker and Stoeckenius to answer this
question: Is ATP synthase required for ATP synthesis? Design the experiment.
23. Both FADH2 and NADH donate electrons to the electron transport chain. Which does it at a
lower energy level?
24. During oxidative phosphorylation, H2O is formed. Where does the oxygen for the synthesis
of the water come from?
A) carbon dioxide (CO2)
B) glucose (C6H12O6)
C) molecular oxygen (O2)
D) pyruvate (C3H3O3-)
E) lactate (C3H5O3-)
See the textbook or lecture slides.
25. Review the citric acid cycle. How many molecules of ATP, NADH, and FADH2 are
generated in the citric acid cycle as a result of the oxidation of one molecule of pyruvate?
26. Review the slides for electron transport in the mitochondria. In your own words explain how
donation of electrons by NADH and FADH2 to the ETC leads to the synthesis of ATP.
27. Review the slides for electron transport in the mitochondria. It is possible to prepare vesicles
from portions of the inner membrane of the mitochondrial components. For oxidative
phosphorylation to be carried on by this isolated inner membrane with its protein complexes
intact, we must provide the required substrates. What are these substrates?
List all of the materials that are supplied on the matrix side of the membrane.
28. Review the slides for electron transport in the mitochondria from lecture notes. Mark the
steps that contribute to the formation of the proton gradient across the membrane.
Consider both movement of protons across the membrane and reactions that remove protons
from the matrix, synthesis of water (not the ones that add protons to the matrix).
29. You have identified a new protein that might act as a cotransporter that moves pyruvate
actively across a membrane using the energy released from the movement of protons down
their gradient. We want to know whether this protein is in fact a pyruvate-proton
contransporter to transport pyruvate against its gradient across a lipid membrane. Design an
experiment to figure this out. To simplify the experimental design you can use an artificial
vesicle (simple lipid bilayer) because you can insert whatever protein you like into the lipid
bilayer of the artificial vesicle. You do not need to describe details of methods. For
example, you can simply state we will measure the voltage across the membrane without
explaining how you will do that (if that applied to your experiment). Describe the elements
of experimental design needed for this new experiment: null and alternative hypotheses,
experimental details including independent and dependent and standardized variables, levels
of treatment, and experimental prediction.
30. Dinitrophenol is an uncoupler. In general terms, what does an uncoupler do? How would it
affect electron transport in the mitochondria? How would it affect ATP synthesis in the
mitochondria? Why would it be even considered as a potential “diet pill”?
Uncouplers dissipate the proton gradient across the membrane and uncouple electron transport
from ATP synthesis…
31. Cyanides attach to the iron within cytochrome c oxidase and inhibit its activity. What would
that do to electron transport in the mitochondria? To the proton gradient? To ATP
synthesis? Why would that make cyanides poisonous to us? Explain.
If cytochrome c oxidase cannot oxidize cytochrome c, what does that mean for electron transport
in the mitochondria? If electrons are not moving from complex to complex, what does that do to
the establishment of a proton gradient? ATP synthesis?
32. Why is it important for complexes I, III, and IV in the mitochondria to be transmembrane
oteins while complex II is not?
33. Plants make and store cyanide in their cells. What is the purpose of cyanide in the plants?
34. If you subject plant mitochondria to cyanide, the plants survive because of the presence of
the alternative oxidase that allows them to bypass complexes III and IV. As far as we know,
is this a defensive mechanism that has evolved to protect the plants against cyanide
Is a plant likely to be poisoned by cyanide?!
35. Plants have an alternative oxidase that allows them to bypass complexes III and IV. This
means electrons from ubiquinone go to this alternative oxidase, which then passes the
electrons to oxygen reducing it to water. Compare the proton gradient established across the
inner mitochondrial membrane, the relative amount of ATP synthesized, and the energy
released as heat when this alternative oxidase is used as opposed to when the normal electron
transport pathway (including complexes III, IV, and cytochrome c) is used.
Consider the role of complexes III and IV in establishing the proton gradient and everything that
follows from that. If electrons are going from ubiquinone to the alternative oxidase and then to
oxygen, what happens to the proton gradient? To the number of ATP molecules produced per
36. Plants have an alternative oxidase that allows them to bypass complexes III and IV. This
allows them to raise their tissue temperatures under certain conditions. Describe two
examples where this could be useful to the plants.
Recall the skunk cabbage melting snow (why is that important?). Some plants like voodoo lilies
volatilize chemicals from their flowers (why is that important?)
37. An organism has a mutation in the pyruvate symporter in the mitochondria. The mutation
makes the symporter 50% as efficient as the normal protein in transporting pyruvate into the
mitochondria. What would be the consequences of this mutation to the organism?
38. In the absence of oxygen fermentation must happen, otherwise glycolysis will stop. This is
regardless of whether it is lactic acid fermentation or alcohol fermentation that is used.
Explain why (refer to figures, but do not memorize them).
NAD+ is needed for glycolysis…
39. Review the figures for fermentation. In each, explain where the redox reaction is. Make sure
to identify the functional groups in the substrate and the final product in each.
40. Why does yeast-based dough rise? Think CO2.
41. Yeast is a facultative anaerobe. What does that mean?