Pyruvate Oxidation (Simplified): Study with Video Lessons, Practice Problems & Examples

Pyruvate oxidation is a crucial step in cellular respiration, where pyruvate, derived from glucose during glycolysis, can follow two pathways based on oxygen availability. In aerobic conditions, pyruvate is converted to Acetyl CoA by the enzyme pyruvate dehydrogenase, reducing NAD⁺ to NADH. This Acetyl CoA enters the Citric Acid Cycle, leading to the production of high-energy molecules like ATP. Conversely, in anaerobic conditions, pyruvate undergoes fermentation. Understanding these pathways is essential for grasping energy production in cells.

Pyruvate Oxidation Concept 1

Hey everyone. Let's take a look, a simplified look at pyruvate oxidation. Now, recall that one glucose molecule is converted to 2 pyruvate molecules through the glycolysis pathway. Now, the fate of pyruvate itself depends on the availability of oxygen in the cells. If we take a look here, remember stage 1 is just hydrolysis of our macromolecules, in this case, carbohydrates.

The carbohydrates through hydrolysis are transformed into glucose molecules. Glucose will undergo glycolysis where it's oxidized into pyruvate. Remember, glucose has 6 carbons. Pyruvate only has 3. That's why there are 2 of them that are being formed.

We're going to say that pyruvate, once it's made, if oxygen is available, we're going to undergo aerobic respiration. That means we'd head this way into Acetyl CoA formation. That Acetyl CoA will then go into the Citric Acid Cycle or Krebs Cycle of stage 3, on its way to the ETC and Oxidative Phosphorylation of stages 4. And at the end, we make our high energy molecules of NADH, FADH₂, and ATP. If oxygen is not available, then we would undergo anaerobic respiration, and that would lead to fermentation.

So, just remember, glycolysis itself helps to oxidize glucose into pyruvate. Pyruvate can take an aerobic respiration pathway with oxygen available, or it could take an anaerobic respiration pathway if oxygen is not available. So those are its two phases.

Pyruvate Oxidation Concept 2

Now, if oxygen is available, we talk about aerobic respiration. We're going to say here, in the presence of oxygen, pyruvate is oxidized by the enzyme pyruvate dehydrogenase to Acetyl CoA. In this process, 1 NAD⁺ is reduced to NADH. So here goes our pyruvate.

We have 1 NAD⁺ being reduced to NADH. We'd say that the acetyl group, this acetyl group here, is transferred to a CoA-SH. This is what gives us Acetyl CoA. And remember, this is catalyzed by the enzyme pyruvate dehydrogenase. This is what you need to keep in mind when we're talking about pyruvate undergoing aerobic respiration.

Pyruvate Oxidation Example 1

Which of the following statements is correct about pyruvate oxidation? It states here that pyruvate oxidation takes place in the absence of oxygen. However, we've been discussing aerobic respiration, in which it's necessary for oxygen to be present in order for our pyruvate dehydrogenase to oxidize, or help oxidize, pyruvate into Acetyl CoA. NADH is oxidized to NAD⁺. We also mentioned that in this aerobic respiration, it's NAD⁺ that's reduced to NADH.

So NAD⁺ is what's oxidizing our pyruvate. Thus, oxygen isn't required as a reactant. That leaves option D. Pyruvate loses one carbon atom in the form of carbon dioxide. Remember, it's the acetyl group that's lost initially from pyruvate, and we're going to say, yes.

We lose a carbon as carbon dioxide. So this would be our answer. And we're losing that carbon dioxide in the beginning, and remember, it's transferred to CoASH. So here, we're going to say the acetyl group that's left behind is transferred to CoASH as a result.

So here, our final answer will be option D.