21. The Generation of Biochemical Energy

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.

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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