During the complete aerobic oxidation of 1 molecule of glucose in a eukaryotic cell, what … — JAMB UTME

During the complete aerobic oxidation of $1$ molecule of glucose in a eukaryotic cell, what is the net number of $\text{ATP}$ molecules produced specifically via substrate-level phosphorylation inside the mitochondrial matrix?

$2$ $\text{ATP}$ moleculesAnswer
B
$4$ $\text{ATP}$ molecules
C
$32$ $\text{ATP}$ molecules
D
$38$ $\text{ATP}$ molecules

Answer

2

\text{ATP}

molecules are produced via substrate-level phosphorylation within the mitochondrial matrix.

In eukaryotic cellular respiration,

1

molecule of glucose undergoes glycolysis to produce

2

molecules of pyruvate (yielding

2

net

\text{ATP}

in the cytoplasm). The pyruvates enter the mitochondrial matrix and convert into

2

acetyl-CoA molecules during the link reaction (yielding

0

\text{ATP}

). Each acetyl-CoA then enters the Krebs cycle in the matrix, where

1

molecule of

\text{ATP}

(or

\text{GTP}

) is generated per turn via substrate-level phosphorylation (specifically at the conversion of succinyl-CoA to succinate). Because

2

turns occur per glucose molecule, exactly

2

\text{ATP}

molecules are produced by substrate-level phosphorylation in the mitochondrial matrix.

Step-by-Step Solution

Identify the cellular site and reaction phase specified in the question

The target site is the mitochondrial matrix, where the link reaction and the Krebs (citric acid) cycle take place.

Glycolysis occurs in the cytoplasm, while oxidative phosphorylation occurs on the inner mitochondrial membrane (cristae).

Analyze the mode of ATP synthesis requested

Substrate-level phosphorylation refers to direct transfer of a phosphate group to ADP, distinct from oxidative phosphorylation driven by the electron transport chain.

The question specifically isolates substrate-level phosphorylation, excluding chemiosmotic ATP synthesis.

Calculate ATP yield per glucose molecule in the mitochondrial matrix

1

molecule of glucose yields

2

molecules of acetyl-CoA, driving

2

turns of the Krebs cycle. Each turn generates

1

\text{ATP}

(or

\text{GTP}

) by substrate-level phosphorylation, giving a total of

2

\text{ATP}

molecules.

No ATP is directly synthesized via substrate-level phosphorylation during the link reaction.

Key Concept

Substrate-level phosphorylation yield during the Krebs cycle

Estimated Time:1m 0s

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