IMAT 2017 Q36 [Glycolysis and Pyruvate Decarboxylation]

Which of the following molecules is/are directly produced during BOTH glycolysis and pyruvate decarboxylation in a healthy human cell?

  1. ATP
  2. carbon dioxide
  3. reduced NAD

A. 1 and 3 only
B. 2 and 3 only
C. 1 only
D. 3 only
E. 1 and 2 only

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The correct answer is D.

To answer this question, we have to know what glycolysis and pyruvate decarboxylation are.

What is glycolysis ?

  • It is a metabolic pathway that begins with a molecule of glucose (6 carbons) and ends with a molecule of pyruvate (3 carbons). Its purpose is to produce energy for the cells to be able to function properly.

  • In the process, 2 molecules of ATP are consumed and 2 NAD molecules are reduced into NADH,H+.

  • The chemical reaction is the following : glucose + 2 ADP + 2 Pi + 2 NAD+ → 2 pyruvate + 2 ATP + 2 (NADH + H+) + 2 H2O.

    It does NOT involve carbon dioxide.

What is pyruvate decarboxylation ?

  • It is a chemical reaction that involves the oxidation of a molecule of pyruvate by the pyruvate deshydrogenase complex. Additionally, a molecule of carbon dioxide is produced.

  • The pyruvate is transformed into acetyl-CoA. The chemical reaction is the following : pyruvate + CoA-SH - NAD+ → acetyl-CoA + NADH,H+ + CO2

    It does not involve ATP

By a process of elimination, we can deduce that the only common molecule to both of these processes is the reduced NAD.