When pyruvic acid reacts with the enzyme Coenzyme A (CoA) in the presence of the enzyme pyruvate dehydrogenase, it forms acetyl-CoA. This reaction is a key step in cellular respiration, specifically in the transition reaction that links glycolysis to the citric acid cycle.

Here's a breakdown of the process:

1. Pyruvic acid is produced at the end of glycolysis.

2. Pyruvate dehydrogenase catalyzes the conversion of pyruvic acid into acetyl-CoA.

3. CoA acts as a carrier molecule, attaching to the acetyl group from pyruvic acid.

4. Carbon dioxide (CO2) is released as a byproduct.

The resulting acetyl-CoA then enters the citric acid cycle, where it is further oxidized to produce energy in the form of ATP.