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Unformatted text preview: 1 Chapter 9 - Cellular Respiration I nt roduction Photosynthesis Photosynthesis is a process in which the energy in sunlight is stored in the chemical bonds of glucose (C 6 H 12 O 6 ) for later use. Carbon dioxide is reduced to glucose and water is oxidized . Oxidation is the loss of an electron or hydrogen atom. Reduction is the gain of an electron or hydrogen atom. Oxidation reactions release energy and reduction reactions store energy in chemical bonds. What is Cellular Respiration? Cellular respiration allows organisms to use (release) the energy stored in glucose. The energy in glucose is first used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transferred to ATP. In respiration, glucose is oxidized (releasing energy) and oxygen is reduced to form water. The carbon atoms of the sugar molecule are released as carbon dioxide (CO 2 ). The complete breakdown of glucose to carbon dioxide and water requires two major steps: 1) glycolysis and 2) aerobic respiration. Glycolysis produces two ATP. Thirty- four more ATP are produced by aerobic pathways if oxygen is present. In the absence of oxygen, fermentation reactions produce alcohol or lactic acid but no additional ATP. Review of Electron Car riers NAD + + 2H NADH + H + FAD + 2H FADH 2 Glycolysis 2 During glycolysis, glucose (C 6 ) is broken down to two molecules of pyruvate (C 3 ). (*Compounds that end in "___ate" can be called "___ic acid". Example lactate is lactic acid and malate is malic acid.) Glycolysis occurs in the cytoplasm ( cytosol ) and does not require oxygen. There are ten steps in glycolysis and each one is catalyzed by a specific enzyme. A brief summary of these reactions is presented here. 2 ATP molecules are used to phosphorylate and activate compounds that will eventually become converted to pyruvate (or pyruvic acid ) (see diagram below). Two hydrogen atoms are removed by NAD + forming 2 NADH (see diagram). Additional phosphorylation results in intermediate 3-carbon molecules with 2 phosphate groups. Four ATP are produced by substrate-level phosphorylation . Recall that substrate-level phosphorylation is the production of ATP using energy from other high-energy compounds but without the use of the electron transport system in the mitochondria....
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