Cellular Respiration: Pyruvate Oxidation - Online Tutor, Practice Problems & Exam Prep

Pyruvate oxidation, the second step of cellular respiration, occurs in the mitochondrial matrix, converting 2 pyruvate molecules from glycolysis into 2 Acetyl CoA molecules. This process also produces 2 NADH and 2 carbon dioxide (CO₂) molecules. During oxidation, pyruvate loses electrons, which are accepted by NAD⁺, forming NADH. Each pyruvate, containing 3 carbon atoms, loses one carbon as CO₂, while the remaining carbons attach to CoA. The Acetyl CoA then enters the Krebs cycle, continuing the energy production process.

Pyruvate Oxidation

In this video, we're going to begin our introduction to pyruvate oxidation. First, we need to recall from our previous lesson videos that the first stage of cellular respiration, or glycolysis, actually results in the production of 2 pyruvate molecules. These 2 pyruvate molecules produced during glycolysis are then transported to the mitochondrial matrix, where the second stage of cellular respiration will occur. Pyruvate oxidation is the second step of cellular respiration.

Pyruvate oxidation will convert each of the pyruvate molecules produced into a molecule known as Acetyl CoA. Pyruvate oxidation occurs in the mitochondrial matrix. Because it is the second step of cellular respiration, it is easy to remember that pyruvate oxidation produces 2 Acetyl CoA molecules, 2 NADH molecules, and 2 CO₂ or carbon dioxide molecules from one glucose that originally enters the cell. In our image below, we show the 4 stages of aerobic cellular respiration. We have already covered glycolysis in our previous lesson video, so we can give this a check.

Glycolysis results in the production of 2 pyruvate molecules, which are then transported to the mitochondrial matrix. The 2nd stage of aerobic cellular respiration, pyruvate oxidation, occurs inside the mitochondria, which is in the background here. Below, another image shows more details of pyruvate oxidation. As its name implies, pyruvate, the starting molecule, ends up getting oxidized, meaning it loses electrons. The NAD⁺ gains these electrons, becoming NADH.

Pyruvate oxidation produces 2 NADH. Notice that each black circle in the pyruvates represents carbon atoms; each pyruvate has 3 carbon atoms. One carbon atom from each pyruvate is lost as a CO₂ molecule, producing 2 CO₂ molecules. The other carbons of the pyruvate get attached to CoA molecules, producing 2 molecules of Acetyl CoA. You can see one molecule of Acetyl CoA here and the second molecule of Acetyl CoA here.

Ultimately, pyruvate oxidation produces 2 NADH, 2 CO₂ molecules, and 2 Acetyl CoA. Since pyruvate oxidation is the second step of cellular respiration, it helps to remember that it produces 2 NADH, 2 CO₂, and 2 Acetyl CoA molecules. This concludes our introduction to pyruvate oxidation. The 2 Acetyl CoA molecules produced are going to make their way to the third step of cellular respiration, the Krebs Cycle. We'll discuss that as we move forward in our course. I'll see you all in our next video.

Each of the following describes the pyruvate oxidation reaction except that _____________________.

• A. It connects glycolysis to the citric acid cycle.
• B. Each pyruvate is converted to an acetyl-CoA molecule.
• C. NAD⁺ is reduced to NADH.
• D. This reaction occurs within the cytoplasm.
• E. Carbon dioxide is released as a by-product.

In aerobic cellular respiration, pyruvate molecules must be transformed through a process called pyruvate oxidation before they can be broken down in the Krebs Cycle. What are the products of pyruvate oxidation?

• A. Acetyl CoA, O₂, and ATP.
• B. Acetyl and CO₂.
• C. Acetyl CoA, FADH₂, and CO₂.
• D. Acetyl CoA, NADH, and CO₂.
• E. Acetyl CoA, NAD⁺, ATP, and CO₂.

Here’s what students ask on this topic:

What is pyruvate oxidation and where does it occur?

Pyruvate oxidation is the second step of cellular respiration, following glycolysis. It occurs in the mitochondrial matrix. During this process, each pyruvate molecule produced from glycolysis is converted into Acetyl CoA. This conversion also produces NADH and carbon dioxide (CO₂). Specifically, pyruvate loses electrons (is oxidized), which are accepted by NAD⁺ to form NADH. Each pyruvate, containing three carbon atoms, loses one carbon as CO₂, while the remaining carbons attach to CoA to form Acetyl CoA.

What are the products of pyruvate oxidation?

Pyruvate oxidation produces three main products from each glucose molecule that enters glycolysis: 2 Acetyl CoA molecules, 2 NADH molecules, and 2 carbon dioxide (CO₂) molecules. Each pyruvate molecule, containing three carbon atoms, loses one carbon as CO₂, while the remaining carbons attach to CoA to form Acetyl CoA. Additionally, NAD⁺ accepts electrons lost from pyruvate, forming NADH.

How does pyruvate oxidation contribute to the Krebs cycle?

Pyruvate oxidation produces Acetyl CoA, which is essential for the Krebs cycle. Each Acetyl CoA molecule generated from pyruvate oxidation enters the Krebs cycle, where it combines with oxaloacetate to form citrate. This initiates a series of reactions that produce ATP, NADH, and FADH₂, which are crucial for the cell's energy production. Thus, pyruvate oxidation is a critical preparatory step that fuels the Krebs cycle.

Why is NADH production important in pyruvate oxidation?

NADH production during pyruvate oxidation is crucial because NADH serves as an electron carrier in cellular respiration. The electrons carried by NADH are later used in the electron transport chain to generate ATP, the cell's primary energy currency. Each NADH molecule can produce approximately 2.5 ATP molecules through oxidative phosphorylation, making NADH a vital component in the cell's energy production process.

What happens to the carbon atoms in pyruvate during pyruvate oxidation?

During pyruvate oxidation, each pyruvate molecule, which contains three carbon atoms, undergoes decarboxylation. One of the three carbon atoms is released as carbon dioxide (CO₂). The remaining two carbon atoms are then attached to Coenzyme A (CoA) to form Acetyl CoA. This process results in the production of two CO₂ molecules and two Acetyl CoA molecules from the two pyruvate molecules generated from one glucose molecule during glycolysis.