Which statement about the citric acid cycle is true?

Which statement about the citric acid cycle is true?

• A. Pyruvate enters mitochondrion and is oxidized into acetyl-CoA followed by a series of redox rxns to create CO2, water, and electron carriers.
• B. Occurs in the cytoplasm producing lactate
• C. Produces glucose from acetyl-CoA
• D. Occurs only during photosynthesis

Answer: (A)

The main idea is that the citric acid cycle happens in the mitochondria and fully oxidizes acetyl-CoA to carbon dioxide while generating energy-rich electron carriers. After glycolysis, pyruvate is transported into the mitochondrion and converted to acetyl-CoA, which then enters the cycle. Through a series of oxidation-reduction steps, CO2 is released and the carriers NADH and FADH2 are produced, providing reducing equivalents for ATP synthesis, with a small amount of direct energy captured as GTP (or ATP) per turn. This is why the statement describing mitochondrial entry of pyruvate, its conversion to acetyl-CoA, and subsequent redox steps that yield CO2 and electron carriers captures the essential truth about the cycle. The other scenarios don’t fit: lactate production occurs in the cytoplasm during anaerobic glycolysis, not in the citric acid cycle; glucose is not produced by the cycle itself (gluconeogenesis can use intermediates from metabolism, but the cycle doesn’t directly make glucose); and the cycle is a mitochondrial process in aerobic organisms, not something that happens only during photosynthesis in chloroplasts.

The main idea is that the citric acid cycle happens in the mitochondria and fully oxidizes acetyl-CoA to carbon dioxide while generating energy-rich electron carriers. After glycolysis, pyruvate is transported into the mitochondrion and converted to acetyl-CoA, which then enters the cycle. Through a series of oxidation-reduction steps, CO2 is released and the carriers NADH and FADH2 are produced, providing reducing equivalents for ATP synthesis, with a small amount of direct energy captured as GTP (or ATP) per turn. This is why the statement describing mitochondrial entry of pyruvate, its conversion to acetyl-CoA, and subsequent redox steps that yield CO2 and electron carriers captures the essential truth about the cycle. The other scenarios don’t fit: lactate production occurs in the cytoplasm during anaerobic glycolysis, not in the citric acid cycle; glucose is not produced by the cycle itself (gluconeogenesis can use intermediates from metabolism, but the cycle doesn’t directly make glucose); and the cycle is a mitochondrial process in aerobic organisms, not something that happens only during photosynthesis in chloroplasts.