Final answer:
Pyruvate is converted into acetyl CoA after glycolysis and before the Citric Acid Cycle (CAC) begins. This step is important because it prepares the pyruvate molecules for entry into the CAC and produces NADH for ATP production.
Step-by-step explanation:
The step that occurs after glycolysis and before the Citric Acid Cycle (CAC) begins is the conversion of pyruvate into acetyl CoA. This step is important because it prepares the three-carbon pyruvate molecules for entry into the CAC. During this conversion, a molecule of CO₂ and two high-energy electrons are removed, which are captured by NADH for later ATP production.