Multiple Choice
In aerobic metabolism, what is the primary function of the citric acid (Krebs) cycle?
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Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism
Citric Acid Cycle 1
Multiple Choice
In one turn of the citric acid (Krebs) cycle per acetyl-CoA (excluding ATP from oxidative phosphorylation), what is the direct energy yield in terms of reduced cofactors and substrate-level phosphorylation?
A
, , and (or ATP equivalent)
B
, , and
C
, , and
D
, , and
Verified step by step guidance1
Identify the key products formed directly in one turn of the citric acid cycle per acetyl-CoA molecule, focusing on reduced cofactors and substrate-level phosphorylation without including ATP from oxidative phosphorylation.
Recall that during the cycle, three specific reactions produce NADH: isocitrate to α-ketoglutarate, α-ketoglutarate to succinyl-CoA, and malate to oxaloacetate. This gives a total of 3 NADH molecules.
Recognize that one FADH2 molecule is produced during the conversion of succinate to fumarate by succinate dehydrogenase.
Note that substrate-level phosphorylation occurs when succinyl-CoA is converted to succinate, producing one GTP (or ATP equivalent) molecule directly.
Summarize the direct energy yield per acetyl-CoA as 3 NADH, 1 FADH2, and 1 GTP (or ATP equivalent), excluding any ATP generated later through oxidative phosphorylation.
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