Question

level 2
q4
before the krebs cycle, pyruvate must be broken down into what molecule?
a. pyruvate coa
b. coenzyme a
c. acetyl coa
d. nadh
diagram: pyruvate structure, coa-sh, oxidation reaction (nad⁺ → nadh + h⁺ + co₂), and acetyl coa structure (s-coa, c=o, ch₃)
options repeated:
○ a. pyruvate coa
○ b. coenzyme a
○ c. acetyl coa
○ d. nadh

Explanation:

In cellular respiration, before the Krebs cycle (citric acid cycle), pyruvate undergoes an oxidation reaction where it is converted into acetyl CoA. This process also produces NADH, releases CO₂, and involves Coenzyme A (CoA - SH) to form acetyl CoA (the molecule with the structure shown: S - CoA attached to the acetyl group). Option A is incorrect as "Pyruvate CoA" is not the correct product. Option B is Coenzyme A, which is a reactant in the reaction, not the product of pyruvate breakdown. Option D is NADH, which is a by - product of the reaction, not the molecule pyruvate is broken down into.

Answer:

C. Acetyl CoA