During the complete aerobic breakdown of one molecule of glucose, how many net molecules o… — JAMB UTME

During the complete aerobic breakdown of one molecule of glucose, how many net molecules of ATP are produced exclusively through substrate-level phosphorylation?

A
$2$ molecules of ATP
$4$ molecules of ATPAnswer
C
$32$ molecules of ATP
D
$38$ molecules of ATP

Answer

4

molecules of ATP

Substrate-level phosphorylation refers to the direct transfer of a phosphate group from a phosphorylated metabolic intermediate to ADP. In full aerobic respiration of one glucose molecule, this occurs twice during glycolysis (yielding a net of

2

ATP in the cytoplasm) and once per turn of the Krebs cycle (yielding

2

ATP total for the

2

acetyl-CoA molecules in the mitochondrial matrix). The total net ATP formed exclusively by substrate-level phosphorylation is therefore

4

molecules.

Step-by-Step Solution

Calculate net ATP produced by substrate-level phosphorylation during glycolysis.

Glycolysis consumes

2

ATP molecules during initial phosphorylation reactions and synthesizes

4

ATP molecules directly from ADP, yielding a net of

2

ATP molecules per glucose.

Glycolytic ATP production occurs in the cytoplasm independent of the electron transport chain.

Calculate ATP (GTP) produced by substrate-level phosphorylation during the Krebs cycle.

Each molecule of glucose produces

2

molecules of acetyl-CoA, driving two turns of the Krebs cycle. Each turn generates

1

ATP (or GTP equivalent) directly via succinyl-CoA synthetase, giving

2

ATP molecules.

Substrate-level phosphorylation occurs when a phosphate group is transferred directly from a high-energy phosphorylated metabolic intermediate to ADP.

Sum the net substrate-level ATP yields.

2 \text{ (from glycolysis)} + 2 \text{ (from Krebs cycle)} = 4 \text{ ATP molecules}

Total substrate-level yield excludes ATP generated downstream by oxidative phosphorylation in the electron transport chain.

Key Concept

Substrate-level Phosphorylation vs Oxidative Phosphorylation

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