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 process generates a net gain of 2 ATP molecules through substrate-level phosphorylation and produces 2 NADH molecules, which serve as electron carriers.

Following glycolysis, the pyruvates are transported into the mitochondrial matrix for pyruvate oxidation. Here, each pyruvate is oxidized, resulting in the formation of 2 acetyl CoA molecules, 2 NADH, and the release of 2 carbon dioxide (CO₂) molecules. The acetyl CoA then enters the citric acid cycle.

The citric acid cycle processes the acetyl CoA, yielding 2 ATP, 6 NADH, and 2 FADH₂ molecules, while releasing 4 CO₂ molecules. This cycle is crucial for extracting high-energy electrons from the acetyl CoA, which are carried by NADH and FADH₂ to the next stage.

In the electron transport chain, the electrons from NADH and FADH₂ are transferred through a series of proteins, creating 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. Oxygen acts as the final electron acceptor, combining with electrons and hydrogen ions to form water.

When calculating the total ATP yield from one glucose molecule, the combined output from all stages ranges from 30 to 38 ATP. This high efficiency highlights the importance of aerobic cellular respiration in energy production for cellular functions.

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 produce any carbon dioxide (CO₂). Glycolysis generates a net gain of 2 ATP and produces 2 NADH electron carriers, which are crucial for the subsequent stages.

Next, during pyruvate oxidation, each of the 2 pyruvate molecules is converted into 2 Acetyl CoA molecules. This step occurs in the mitochondria and results in the release of 2 CO₂ molecules (one from each pyruvate). No ATP or FADH₂ is produced in this stage, but it does yield 2 NADH.

The Krebs cycle begins with the 2 Acetyl CoA molecules. Throughout this cycle, a total of 4 CO₂ molecules are released, and 2 ATP, 2 FADH₂, and 6 NADH are produced. The cycle regenerates oxaloacetate, which is necessary for the continuation of the cycle, thus emphasizing its cyclical nature.

Finally, oxidative phosphorylation is where the majority of ATP is generated. 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 process culminates in the formation of water (H₂O) when oxygen acts as the final electron acceptor, combining with hydrogen ions.

In summary, from one molecule of glucose, aerobic cellular respiration produces a total of 6 CO₂, approximately 30 to 38 ATP, 2 FADH₂, and 10 NADH. This efficient energy conversion process is vital for cellular functions and overall metabolism.