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Multiple Choice
In the glycolytic pathway (from one molecule of glucose to two molecules of pyruvate), what is the net number of ATP molecules produced by substrate-level phosphorylation?
A
ATP (net)
B
ATP (net)
C
ATP (net)
D
ATP (net)
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Verified step by step guidance
1
Begin by recalling the overall process of glycolysis, which converts one molecule of glucose into two molecules of pyruvate through a series of enzymatic reactions.
Identify the steps in glycolysis where substrate-level phosphorylation occurs. These are the reactions that directly generate ATP by transferring a phosphate group to ADP.
Note that there are two key substrate-level phosphorylation steps in glycolysis: one catalyzed by phosphoglycerate kinase and another by pyruvate kinase. Each of these steps produces ATP.
Since glycolysis produces two molecules of pyruvate from one glucose, each substrate-level phosphorylation step happens twice per glucose molecule, doubling the ATP produced in these steps.
Calculate the net ATP by subtracting the ATP invested in the early steps of glycolysis (2 ATP used) from the total ATP produced by substrate-level phosphorylation (4 ATP produced), resulting in the net ATP yield.