21. The Generation of Biochemical Energy

Which reaction of the citric acid cycle produces ATP directly?

Identify the two reactions that involve oxidation and decarboxylation.

Write the name for the substrate, enzyme, and product of reaction 6 of the citric acid cycle.

Write the name of the substrate and the enzyme of reaction 8 of the citric acid cycle.

What is the name of the enzyme for the reaction that produces a GTP molecule in the citric acid cycle?

Which reactions of the citric acid cycle produce NADH?

Complete the following net equation for one turn of the citric acid cycle.

Acetyl CoA + __H₂O + 3 NAD+ + FAD + GDP + ____ ⭢  CoA + ___NADH + ___H⁺ + FADH₂ + GTP + ___CO₂

Look ahead to Figure 21.8 for the citric acid cycle.

a. Draw the structures of the reactants in steps 3, 6, and 8, and indicate which hydrogen atoms are removed in these reactions.

Why, do you suppose, the coenzyme for the reaction in the citric acid cycle that is catalyzed by succinate dehydrogenase is FAD and not NAD⁺?

Identify the participants in the citric acid cycle that contain alcohol groups. Identify these groups as primary, secondary, or tertiary alcohols.

Which of the reactants in the citric acid cycle have two chiral carbon atoms?

Since no molecular oxygen participates in the citric acid cycle, the steps in which acetyl groups are oxidized to CO₂ involve removal of hydride ions and hydrogen ions. What is the acceptor of hydride ions? What is the acceptor of hydrogen ions?

What is the final fate of the carbons in acetyl-CoA after several turns of the citric acid cycle?

Look at the eight steps of the citric acid cycle (Figure 21.8) and answer the following questions:

a. Which steps involve oxidation reactions?

Look at the eight steps of the citric acid cycle (Figure 21.8) and answer the following questions:

b. Which steps involve decarboxylation (loss of CO₂)?

Look at the eight steps of the citric acid cycle (Figure 21.8) and answer the following questions:

c. Which step or steps involve a hydration reaction?

Look ahead to Figure 21.8 for the citric acid cycle.

b. What class of enzymes carry out these reactions?

We talk of burning food in a combustion process, producing CO₂ and H₂O from food and O₂. Explain how O₂ is involved in the process although no O₂ is directly involved in the citric acid cycle.

The citric acid cycle contains four 4-carbon dicarboxylic acids.

a. Name them.

The citric acid cycle contains four 4-carbon dicarboxylic acids.

b. Arrange them in order from least oxidized to most oxidized.

How many NADH and how many FADH₂ molecules are formed in the citric acid cycle?

Which reactions of the citric acid cycle transfer energy as FADH₂?

Which reactions of the citric acid cycle transfer energy as NADH?

What would happen to the citric acid cycle if NADH and FADH₂ were not reoxidized?

Identify the reaction(s) of the citric acid cycle that involve(s)

a. oxidation and decarboxylation

Identify the reaction(s) of the citric acid cycle that involve(s)

c. hydration

What is the total NADH and total FADH₂ produced in one turn of the citric acid cycle?

Refer to the diagram of the citric acid cycle in Figure 18.13 to answer each of the following:

b. How is the number of carbon atoms decreased?

Refer to the diagram of the citric acid cycle in Figure 18.13 to answer each of the following:

d. What are the decarboxylation reactions?

Refer to the diagram of the citric acid cycle in Figure 18.13 to answer each of the following:

b. What are the four-carbon compounds?

Refer to the diagram of the citric acid cycle in Figure 18.13 to answer each of the following:

d. In which reactions are secondary alcohols oxidized?

If there are no reactions in the citric acid cycle that use oxygen, O₂, why does the cycle operate only in aerobic conditions? (18.5)

 Match the following ATP yields to reactions a to g: (18.4, 18.5, 18.6)

1.5 ATP 2.5 ATP 7 ATP 10 ATP

12 ATP 32 ATP 36 ATP

d. Acetyl CoA goes through one turn of the citric acid cycle.

Which of the following molecules will produce the most ATP per mole? (18.5, 18.6)

e. α-ketoglutarate or fumarate in one turn of the citric acid cycle

Name the reactions in the citric acid cycle that involve oxidative decarboxylation.

Name the reaction of the citric acid cycle that reduces FAD.

Refer to the diagram of the citric acid cycle in Figure 12.11 to answer each of the following:

d. Name the reactions where secondary alcohols are oxidized to ketones.

Refer to the diagram of the citric acid cycle in Figure 12.11 to answer each of the following:

c. Name the reaction that is coupled to GTP formation.