Cellular respiration is the process by which cells convert glucose and oxygen into energy, carbon dioxide, and water. It consists of several key steps, which can be broken down into the following:
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Glycolysis: This first step occurs in the cytoplasm where one molecule of glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (three-carbon compounds). This process produces a small amount of ATP (energy) and NADH (an electron carrier). Glycolysis does not require oxygen.
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Pyruvate Oxidation: The pyruvate produced in glycolysis is transported into the mitochondria. Each pyruvate is converted into acetyl-CoA, while releasing one molecule of carbon dioxide (CO₂) as a byproduct. This step also produces NADH from NAD⁺.
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Citric Acid Cycle (Krebs Cycle): Acetyl-CoA enters the citric acid cycle, which takes place in the mitochondria. During this cycle, more carbon dioxide (CO₂) is produced as a waste product. In addition, energy-rich electron carriers (NADH and FADH₂) and a small amount of ATP are generated.
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Oxidative Phosphorylation: This final step occurs in the inner mitochondrial membrane and involves the electron transport chain and chemiosmosis. The NADH and FADH₂ produced in the previous steps are used to donate electrons to the electron transport chain, leading to the production of a large amount of ATP. Oxygen acts as the final electron acceptor, forming water (H₂O), but carbon dioxide is not directly produced in this step.
Carbon Dioxide Release: The steps that release carbon dioxide are the pyruvate oxidation (when pyruvate is converted to acetyl-CoA) and the citric acid cycle (where CO₂ is released during the metabolic reactions).