Question

The citric acid cycle is a series of oxidation reactions that removes carbon atoms

from substrates in the form of CO2. Once a molecule of acetyl CoA enters the
citric acid cycle, how many complete cycles are required for both of the carbon
atoms in its acetyl groupto be oxidized to CO2?_____
(a) 1
(b) 2
(c) 3
(d) 4

Answer 1

Both carbon atoms from a single acetyl CoA molecule are completely oxidized to CO2 in one complete citric acid cycle, producing three NADH, one FADH2, and one ATP (or GTP).

Step-by-step explanation:

Once a molecule of acetyl CoA enters the citric acid cycle, both carbon atoms of its acetyl group are oxidized to CO2 in a single cycle. To elaborate, the acetyl group from acetyl CoA combines with a four-carbon molecule called oxaloacetate to form a six-carbon citrate molecule. As the cycle proceeds, citrate is oxidized, and two carbon dioxide molecules are released for each acetyl group that entered the cycle. Therefore, it takes one complete cycle for both carbon atoms in the acetyl group to be oxidized to CO2. This is because the citric acid cycle is designed to fully oxidize the two-carbon acetyl group into two molecules of carbon dioxide, generating in the process three NADH, one FADH2, and one ATP (or GTP) through substrate-level phosphorylation.