Question

Each molecule of pyruvic acid entering the Krebs cycle produces

• A. 2 molecules of $C{O}_2$
• B. 3 molecule of $C{O}_2$
• C. 1 molecule of $C{O}_2$
• D. 5 molecule of $C{O}_2$

Answer 1

Answer: (B)

3 molecule of $C{O}_2$

The pyruvic acid gets converted to acetyl coenzyme A which enters the Krebs cycle. Pyruvate oxidation converts pyruvate, a three-carbon molecule into acetyl-CoA, a two-carbon molecule attached to Coenzyme A—producing a NADH and releasing one carbon dioxide molecule in the process. Acetyl CoA acts as fuel for the citric acid cycle in the next stage of cellular respiration.

1. Two molecules of pyruvate are converted into two molecules of acetyl-CoA.
   
2. Two carbons are released as carbon dioxide—out of the six originally present in glucose.
   
3. 2NADH are generated from NAD+.
   

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