Glycolysis
Glycolysis occurs in the cytoplasm and is the first stage in both aerobic and anaerobic respiration. During this process, glucose is phosphorylated, creating unstable fructose bisphosphate, which then undergoes oxidation to form pyruvate. This generates ATP and NADH.
The Link Reaction
If oxygen is present, the link reaction joins glycolysis to the Krebs Cycle. In this step, pyruvate is converted to acetate, and then combined with coenzyme A to produce acetyl coenzyme A, releasing carbon dioxide in the process.
The Krebs Cycle
The Krebs Cycle occurs in the mitochondrial matrix, where pyruvate is oxidized to form acetate, producing reduced NAD and releasing a molecule of carbon dioxide. This process also results in the generation of ATP, reduced NAD, and reduced FAD through a series of redox reactions and substrate level phosphorylation.
Oxidative Phosphorylation
Oxidative phosphorylation, the last stage of aerobic respiration, takes place in the inner mitochondrial membrane and results in the production of many ATP molecules and the production of water from oxygen. This process involves a series of steps including the splitting of hydrogen atoms, the release of energy as electrons move through the electron transport chain, and the establishment of a concentration gradient of protons/hydrogen ions between the matrix and the inner membrane space.
Anaerobic Respiration
This occurs when cells have little to no oxygen and can lead to the production of lactate in animals or ethanol in plants as byproducts.
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