During aerobic respiration in eukaryotic cells, pyruvate produced during glycolysis is tra… — JAMB UTME

During aerobic respiration in eukaryotic cells, pyruvate produced during glycolysis is transported into the mitochondrial matrix. What are the net coenzymes and gaseous by-products formed when two molecules of pyruvate undergo the link reaction prior to entering the Krebs cycle?

$2\text{ NADH}$ and $2\text{ CO}_2$ Answer
B
$2\text{ FADH}_2$ and $2\text{ CO}_2$
C
$2\text{ ATP}$ and $2\text{ NADH}$
D
$4\text{ NADH}$ and $4\text{ CO}_2$

Answer

The link reaction produces

2\text{ NADH}

and

2\text{ CO}_2

per glucose molecule (two pyruvate molecules).

In the mitochondrial matrix, each of the two pyruvate molecules undergoes oxidative decarboxylation to form acetyl-CoA. This step releases one molecule of carbon dioxide gas and reduces one molecule of

NAD^+

NADH

per pyruvate. Consequently, two pyruvate molecules produce a net total of

2\text{ NADH}

and

2\text{ CO}_2

, without generating ATP directly.

Step-by-Step Solution

Identify the chemical pathway and starting substrates

Glycolysis breaks down one glucose molecule into two 3-carbon pyruvate molecules in the cytoplasm.

The link reaction processes pyruvate in the mitochondrial matrix.

Analyze the stoichiometry of oxidative decarboxylation per pyruvate molecule

Each 3-carbon pyruvate loses one carbon as

CO_2

and is oxidized to reduce

1\text{ NAD}^+

1\text{ NADH}

, forming a 2-carbon acetyl group attached to Coenzyme A.

The enzyme pyruvate dehydrogenase catalyzes decarboxylation and oxidation simultaneously.

Multiply the yield by two for a full glucose equivalent

For two pyruvate molecules, the total yields are

2\text{ acetyl-CoA}

2\text{ NADH}

, and

2\text{ CO}_2

, with zero direct ATP generation.

One mole of glucose yields two moles of pyruvate.

Key Concept

Oxidative decarboxylation of pyruvate during the link reaction

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