Unlike an uncontrolled reaction the electron transport chain passes electrons

Unlike an uncontrolled reaction the electron

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Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction O 2 pulls electrons down the chain in an energy-yielding tumble The energy yielded is used to regenerate ATP The Stages of Cellular Respiration: A Preview Harvesting of energy from glucose has three stages Glycolysis (breaks down glucose into two molecules of pyruvate) The citric acid cycle (completes the breakdown of glucose) Oxidative phosphorylation (accounts for most of the ATP synthesis) The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
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A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate- level phosphorylation For each molecule of glucose degraded to CO 2 and water by respiration, the cell makes up to 32 molecules of ATP Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate Glycolysis occurs in the cytoplasm and has two major phases Energy investment phase Energy payoff phase Glycolysis occurs whether or not O 2 is present Concept 9.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules In the presence of O 2 , pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed Oxidation of Pyruvate to Acetyl CoA Before the citric acid cycle can begin, pyruvate must be converted to acetyl Coenzyme A ( acetyl CoA ), which links glycolysis to the citric acid cycle This step is carried out by a multienzyme complex that catalyses three reactions The Citric Acid Cycle The citric acid cycle, also called the Krebs cycle, completes the break down of pyruvate to CO 2 The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH 2 per turn The citric acid cycle has eight steps, each catalyzed by a specific enzyme The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle The NADH and FADH 2 produced by the cycle relay electrons extracted from food to the electron transport chain
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Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and the citric acid cycle, NADH and FADH 2 account for most of the energy extracted from food These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
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