Review of Aerobic Cellular Respiration: Videos & Practice Problems

Aerobic cellular respiration is a vital process that occurs primarily in the mitochondria, where glucose is broken down to produce energy in the form of ATP. This process consists of four main stages: glycolysis, pyruvate oxidation, the citric acid cycle (Krebs cycle), and the electron transport chain.

The first stage, glycolysis, takes place in the cytoplasm and involves the breakdown of glucose, a six-carbon sugar, into two three-carbon pyruvate molecules. This stage also produces two NADH molecules, which serve as electron carriers, and a net gain of two ATP molecules through substrate-level phosphorylation. The term "glycolysis" derives from the Greek words "glyco," meaning sugar, and "lysis," meaning to break down.

Following glycolysis, the pyruvates are transported into the mitochondrial matrix for pyruvate oxidation. Here, each pyruvate is oxidized, resulting in the formation of two Acetyl CoA molecules, two additional NADH molecules, and the release of two carbon dioxide (CO₂) molecules. Each pyruvate contributes three carbon atoms, with one carbon atom released as CO₂ during this process.

The Acetyl CoA then enters the citric acid cycle, where it undergoes a series of reactions that produce two ATP molecules, six NADH molecules, and two FADH₂ molecules, while releasing four CO₂ molecules. This cycle is crucial for extracting high-energy electrons from Acetyl CoA, which are carried by NADH and FADH₂ to the next stage.

The final stage, the electron transport chain, utilizes the electrons from NADH and FADH₂ to create a hydrogen ion concentration gradient across the inner mitochondrial membrane. This gradient drives ATP synthesis through a process called chemiosmosis, resulting in the production of 26 to 34 ATP molecules via oxidative phosphorylation. Additionally, six oxygen molecules act as the final electron acceptors, forming six water molecules as a byproduct.

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 breakdown of glucose not only provides energy but also releases carbon dioxide, which is exhaled as a waste product. Understanding these stages and their outputs is essential for grasping how cells generate energy to sustain life.

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 the first stage, glycolysis, a single glucose molecule (C₆H₁₂O₆) is broken down into two pyruvate molecules. This process occurs in the cytoplasm and does not require oxygen. Glycolysis produces a net gain of 2 ATP molecules and generates 2 NADH electron carriers, while no carbon dioxide (CO₂) is released.

The second stage, pyruvate oxidation, takes the 2 pyruvate molecules produced in glycolysis and converts them into 2 Acetyl CoA molecules. During this conversion, 2 CO₂ molecules are released, and 2 NADH molecules are generated. Notably, no ATP or FADH₂ is produced in this step.

Next, the Krebs cycle begins with the 2 Acetyl CoA molecules. This cycle occurs in the mitochondria and results in the production of 4 CO₂, 2 ATP, 2 FADH₂, and 6 NADH molecules. The cycle regenerates oxaloacetate, which is necessary for the continuation of the cycle, thus emphasizing its cyclical nature.

Finally, oxidative phosphorylation is the stage where the majority of ATP is produced. The electron carriers NADH and FADH₂ donate electrons to the electron transport chain, leading to the production of 26 to 34 ATP molecules. Importantly, no CO₂ is produced in this stage, and the final electron acceptor is oxygen, which combines with hydrogen ions to form water (H₂O).

In summary, the total products from one glucose molecule during aerobic cellular respiration are as follows: 6 CO₂ molecules, 30 to 38 ATP molecules, 2 FADH₂, and 10 NADH. This comprehensive breakdown illustrates how glucose is efficiently converted into energy, highlighting the importance of each stage in the overall process of cellular respiration.