Review of Aerobic Cellular Respiration: Videos & Practice Problems

Aerobic cellular respiration consists of four stages: glycolysis, pyruvate oxidation, the Krebs cycle, and oxidative phosphorylation. Glycolysis breaks down glucose into 2 pyruvates, producing 2 ATP and 2 NADH. Pyruvate oxidation converts pyruvates into acetyl CoA, yielding 2 NADH and releasing 2 CO2. The Krebs cycle generates 2 ATP, 6 NADH, and 2 FADH2 while releasing 4 CO2. Finally, oxidative phosphorylation produces 26-34 ATP through the electron transport chain, utilizing oxygen as the final electron acceptor, resulting in water formation. Overall, 30-38 ATP are produced from one glucose molecule.

Review of Aerobic Cellular Respiration

Aerobic cellular respiration is a vital process that occurs primarily in the mitochondria, with the initial step, glycolysis, taking place in the cytoplasm. This process can be divided into four key stages: glycolysis, pyruvate oxidation, the citric acid cycle (Krebs cycle), and the electron transport chain.

Glycolysis begins with the breakdown of glucose, a six-carbon monosaccharide, into two pyruvate molecules. This stage produces a net gain of 2 ATP through substrate-level phosphorylation and generates 2 NADH molecules, which serve as electron carriers. The pyruvates then enter the mitochondrial matrix for pyruvate oxidation, where they are oxidized to form 2 acetyl CoA molecules and release 2 carbon dioxide (CO₂) molecules.

Next, the acetyl CoA molecules enter the citric acid cycle. Here, each acetyl CoA contributes to the production of 2 ATP, 6 NADH, and 2 FADH₂, while releasing 4 CO₂ molecules. This cycle ensures that all 6 carbon atoms from the original glucose are ultimately released as carbon dioxide.

The final stage, the electron transport chain, utilizes the NADH and FADH₂ produced in earlier stages. As electrons are transferred through the chain, a hydrogen ion concentration gradient is established, leading to ATP production via chemiosmosis. This stage is responsible for generating the majority of ATP, producing between 26 to 34 ATP molecules through oxidative phosphorylation.

In total, aerobic cellular respiration can yield between 30 to 38 ATP molecules from a single glucose molecule, making it an incredibly efficient energy-producing process. The overall reaction also involves oxygen, which acts as the final electron acceptor, forming water as a byproduct. This comprehensive understanding of aerobic cellular respiration highlights its significance in energy metabolism and cellular function.

Through the first three stages of cellular respiration only 4 ATP molecules have been produced from the initial glucose molecule. In which of the products of these stages is the potential energy to produce more ATP molecules stored?

• A. The 6 molecules of CO₂.
• B. The H⁺ ions produced.
• C. The 10 NADH and 2 FADH₂ molecules.
• D. The 4 molecules of ATP.

Answer: (C)

Total Products for Each Stage of Aerobic Cellular Respiration

Aerobic cellular respiration is a multi-step process that converts glucose into usable energy in the form of ATP. This process consists of four main stages: glycolysis, pyruvate oxidation, the Krebs cycle (or citric acid cycle), and oxidative phosphorylation, which includes the electron transport chain and chemiosmosis.

In glycolysis, which occurs in the cytoplasm, a single glucose molecule (C₆H₁₂O₆) is broken down into two pyruvate molecules. This stage produces no carbon dioxide (CO₂), generates a net gain of 2 ATP, and produces 2 NADH electron carriers. The overall reaction can be summarized as:

Glucose → 2 Pyruvate + 2 ATP + 2 NADH

Next, during pyruvate oxidation, each pyruvate is converted into Acetyl CoA, releasing 2 CO₂ molecules in total (one from each pyruvate). This stage does not produce any ATP or FADH₂, but it generates 2 NADH. The reaction can be summarized as:

2 Pyruvate → 2 Acetyl CoA + 2 CO₂ + 2 NADH

The Krebs cycle begins with the Acetyl CoA produced in the previous step. For each Acetyl CoA that enters the cycle, a total of 4 CO₂ molecules are released, along with 2 ATP, 2 FADH₂, and 6 NADH. The cycle regenerates oxaloacetate, which is necessary for the continuation of the cycle. The overall reaction can be summarized as:

2 Acetyl CoA → 4 CO₂ + 2 ATP + 2 FADH₂ + 6 NADH

Finally, oxidative phosphorylation occurs in the inner mitochondrial membrane, where the electron carriers NADH and FADH₂ donate electrons to the electron transport chain. This process does not produce any CO₂ but generates a significant amount of ATP, typically between 26 to 34 ATP molecules, depending on the efficiency of the process. The final electron acceptor is oxygen, which combines with hydrogen ions to form water (H₂O). The overall reaction can be summarized as:

NADH + FADH₂ + O₂ → H₂O + 26-34 ATP

In total, aerobic cellular respiration from one glucose molecule yields approximately 30 to 38 ATP, 6 CO₂, 2 FADH₂, and 10 NADH. The complete breakdown of glucose illustrates how energy is efficiently harvested and utilized by living organisms.

Water is one of the products of aerobic cellular respiration. What is the source of the oxygen atom utilized to create the water molecules?

• A. Carbon dioxide (CO₂).
• B. Glucose (C₆H₁₂O₆).
• C. Oxygen gas (O₂).
• D. Pyruvate (C₃H₃O₃^–).

Answer: (C)

Approximately how many molecules of ATP are produced from the complete oxidation of one molecule of glucose (C₆H₁₂O₆) through the process of aerobic cellular respiration?

• A. 4.
• B. 2.
• C. 26-34.
• D. 30-38.

Answer: (D)

Here’s what students ask on this topic:

What are the four stages of aerobic cellular respiration?

The four stages of aerobic cellular respiration are:

1. Glycolysis: This occurs in the cytoplasm and breaks down glucose into 2 pyruvate molecules, producing 2 ATP and 2 NADH.

2. Pyruvate Oxidation: This occurs in the mitochondrial matrix, converting pyruvate into acetyl CoA, yielding 2 NADH and releasing 2 CO₂.

3. Krebs Cycle (Citric Acid Cycle): This also occurs in the mitochondrial matrix and generates 2 ATP, 6 NADH, and 2 FADH₂ while releasing 4 CO₂.

4. Oxidative Phosphorylation: This occurs in the inner mitochondrial membrane and produces 26-34 ATP through the electron transport chain and chemiosmosis, utilizing oxygen as the final electron acceptor, resulting in water formation.

How many ATP molecules are produced in each stage of aerobic cellular respiration?

In aerobic cellular respiration, the ATP production is as follows:

1. Glycolysis: Produces a net of 2 ATP.

2. Pyruvate Oxidation: Produces 0 ATP.

3. Krebs Cycle (Citric Acid Cycle): Produces 2 ATP.

4. Oxidative Phosphorylation: Produces 26-34 ATP.

Overall, the total ATP produced from one glucose molecule ranges from 30 to 38 ATP.

What is the role of NADH and FADH₂ in aerobic cellular respiration?

NADH and FADH₂ are crucial electron carriers in aerobic cellular respiration. They transport high-energy electrons to the electron transport chain (ETC) in the inner mitochondrial membrane. During oxidative phosphorylation, these electrons pass through the ETC, creating a proton gradient that drives ATP synthesis via chemiosmosis. NADH contributes to the production of approximately 3 ATP per molecule, while FADH₂ contributes to about 2 ATP per molecule. Ultimately, NADH and FADH₂ facilitate the generation of the majority of ATP in cellular respiration.

What happens to the carbon atoms in glucose during aerobic cellular respiration?

During aerobic cellular respiration, the 6 carbon atoms in glucose are fully oxidized and converted into carbon dioxide (CO₂). In glycolysis, glucose (C₆H₁₂O₆) is broken down into 2 pyruvate molecules, each containing 3 carbon atoms. During pyruvate oxidation, each pyruvate loses one carbon atom as CO₂. The remaining 2 carbon atoms from each pyruvate enter the Krebs cycle as acetyl CoA, where they are further oxidized, releasing 4 more CO₂ molecules. In total, 6 CO₂ molecules are produced and exhaled as waste.

What is the final electron acceptor in the electron transport chain?

The final electron acceptor in the electron transport chain (ETC) is molecular oxygen (O₂). Oxygen accepts electrons at the end of the ETC and combines with protons (H⁺) to form water (H₂O). This reaction is crucial because it ensures the continuous flow of electrons through the ETC, allowing for the generation of a proton gradient that drives ATP synthesis through chemiosmosis. Without oxygen, the ETC would halt, and ATP production would be significantly impaired.