Question

1. what happens to pyruvate before it enters the citric acid cycle? what product acts as the first \step\ of the citric acid cycle?
2. for each of the main products of the citric acid cycle, list the number of molecules present at the end of the process:

a. nadh (not counting pyruvate oxidation):
b. fadh2:
c. atp:
d. co2

1. describe the role of nadh and fadh2 in the citric acid cycle.

Explanation:

• Question 2: Pyruvate undergoes pyruvate oxidation. It is converted to acetyl - CoA. Acetyl - CoA then combines with oxaloacetate to form citrate, which is the first step of the citric acid cycle.
• Question 3:
• a. NADH: For each acetyl - CoA entering the citric acid cycle, 3 molecules of NADH are produced.
• b. FADH₂: 1 molecule of FADH₂ is produced per acetyl - CoA.
• c. ATP: 1 molecule of ATP (or GTP, which is equivalent in energy) is produced per acetyl - CoA.
• d. CO₂: 2 molecules of CO₂ are produced per acetyl - CoA.
• Question 4: NADH and FADH₂ are electron carriers. They carry high - energy electrons from the citric acid cycle to the electron transport chain. In the electron transport chain, these electrons are used to generate ATP through oxidative phosphorylation.

Answer:

• Question 2: Pyruvate is converted to acetyl - CoA. Citrate is the first step.
• Question 3:
• a. 3
• b. 1
• c. 1
• d. 2
• Question 4: NADH and FADH₂ are electron carriers that transport electrons to the electron transport chain for ATP production.