Question

The citric acid cycle is a central metabolic pathway in mammalian organisms. Which of the following statements are true regarding its products and its regulation?

A. The pathway leads to the net synthesis of OAA.
B. If the pathway is fed α-ketoglutarate (from the amino acid Glu) it will lead to the net synthesis of OAA.
C. Accumulation of NADH will result in decreased flux of this pathway.
D. It results in the production of 3 NADH, 1 FADH₂, 1 GTP, and 3 CO₂.
E. All of the above.
F. A), B), and C).
G. B) and C).

Answer 1

The citric acid cycle produces two carbon dioxide molecules, three NADH molecules, one FADH₂ molecule, and one ATP or GTP per turn. Its regulation is influenced by ATP, NADH, and ADP levels.

Step-by-step explanation:

In the citric acid cycle, also known as the TCA cycle or the Krebs cycle, acetyl CoA combines with oxaloacetate to form citrate, a six-carbon molecule. During a series of steps, citrate is oxidized, releasing two carbon dioxide molecules for each acetyl group fed into the cycle. This process produces three NADH molecules, one FADH₂ molecule, and one ATP or GTP (depending on the cell type) through substrate-level phosphorylation.

The regulation of the citric acid cycle is influenced by ATP and NADH levels. When adequate ATP and NADH levels are available, the rates of certain reactions in the pathway decrease. Conversely, when more ATP is needed (indicated by rising ADP levels), the rate of these reactions increases. The accumulation of NADH also results in a decreased flux of the citric acid cycle.

In summary, the citric acid cycle produces two carbon dioxide molecules, three NADH molecules, one FADH₂ molecule, and one ATP or GTP (depending on the cell type) per turn of the cycle. Its regulation is influenced by ATP, NADH, and ADP levels.