Breakdown of Pyruvate

Breakdown of Pyruvate

In order for pyruvate, the product of glycolysis, to enter the next pathway, it must undergo several changes. The conversion is a three-step process (see the figure below).

Step 1:

A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium. The result of this step is a two-carbon hydroxyethyl group bound to the enzyme (pyruvate dehydrogenase). This is the first of the six carbons from the original glucose molecule to be removed.

This step proceeds twice (remember: there are two pyruvate molecules produced at the end of glycolsis) for every molecule of glucose metabolized; thus, two of the six carbons will have been removed at the end of both steps.

Step 2:

The hydroxyethyl group is oxidized to an acetyl group, and the electrons are picked up by NAD⁺, forming NADH. The high-energy electrons from NADH will be used later to generate ATP.

Step 3:

The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA.

Upon entering the mitochondrial matrix, a multi-enzyme complex converts pyruvate into acetyl CoA. In the process, carbon dioxide is released and one molecule of NADH is formed.

Note that during the second stage of glucose metabolism, whenever a carbon atom is removed, it is bound to two oxygen atoms, producing carbon dioxide, one of the major end products of cellular respiration.