Multiple Choice
In eukaryotic cells, the Krebs (citric acid) cycle primarily takes place in which cellular location?
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Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism
Citric Acid Cycle 1
Multiple Choice
In the citric acid (Krebs) cycle, how much ATP (or equivalent GTP) is produced directly by substrate-level phosphorylation per turn of the cycle for one acetyl-CoA?
A
ATP (or GTP)
B
ATP (or GTP)
C
ATP (or GTP)
D
ATP (or GTP)
Verified step by step guidance1
Identify the step in the citric acid cycle where substrate-level phosphorylation occurs. This is the step where a direct synthesis of ATP (or GTP) from ADP (or GDP) happens without involving the electron transport chain.
Recall that substrate-level phosphorylation in the citric acid cycle occurs during the conversion of succinyl-CoA to succinate, catalyzed by the enzyme succinyl-CoA synthetase.
Understand that this reaction produces one molecule of GTP (or ATP, depending on the cell type) per turn of the cycle for each acetyl-CoA molecule entering the cycle.
Note that other ATP equivalents produced in the citric acid cycle come from oxidative phosphorylation via NADH and FADH2, not directly from substrate-level phosphorylation.
Conclude that the amount of ATP (or GTP) produced directly by substrate-level phosphorylation per acetyl-CoA turn in the citric acid cycle is one molecule.
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