What combines NAD+ with pyruvate to form NADH and acetyl coenzyme A?

The transition stage, also known as the link reaction or pyruvate dehydrogenase complex, is the process that connects glycolysis to the Krebs cycle. During this stage, pyruvate generated from glycolysis is converted into acetyl coenzyme A (acetyl-CoA) and carbon dioxide.

In this reaction, NAD+ is reduced to NADH as it accepts electrons. This is a crucial step because NADH plays a significant role in the cellular respiration process, as it carries high-energy electrons to the electron transport chain, ultimately contributing to ATP production. Acetyl-CoA then enters the Krebs cycle, where it is further oxidized for energy extraction.

Although glycolysis does produce NADH, it does not combine NAD+ with pyruvate; rather, it breaks down glucose into two molecules of pyruvate, along with producing a small amount of NADH. The Krebs cycle operates on acetyl-CoA but does not start with pyruvate. The electron transport chain is responsible for the final steps of energy production using NADH and FADH2 but does not involve the combination of NAD+ with pyruvate.

Thus, the transition stage is specifically responsible for combining NAD+ with pyruvate to produce NAD