Biology Chapter 8

Biology Chapter 8 - 8.1 Cellular Respiration 1 Cellular...

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8.1 Cellular Respiration 1. Cellular respiration involves various metabolic pathways that break down carbohydrates and other metabolites with the concomitant buildup of ATP. 2. Cellular respiration consumes oxygen and produces CO 2 ; because oxygen is required, cellular respiration is aerobic . 3. Cellular respiration usually involves the complete breakdown of glucose into CO 2 and H 2 O. 4. The net equation for glucose breakdown is: C 6 H 12 O 6 + 6 O 2 = 6 CO 2 + 6 H 2 O + energy 5. Glucose is a high-energy molecule; CO 2 and H 2 O are low-energy molecules; cellular respiration is thus exergonic because it releases energy. 6. Electrons are removed from substrates and received by oxygen, which combines with H + to become water. 7. Glucose is oxidized and O 2 is reduced. 8. The buildup of ATP is an endergonic reaction (i.e., requires energy). 9. The reactions of cellular respiration allow energy in glucose to be released slowly; therefore ATP is produced gradually. 10. In contrast, if glucose were broken down rapidly, most of its energy would be lost as non-usable heat. 11. The breakdown of glucose yields synthesis of 36 or 38 ATP (depending on certain conditions); this preserves about 39% of the energy available in glucose. 12. This is relatively efficient compared to, for example, the 25% efficiency of a car burning gasoline. B. NAD + and FAD 1. Each metabolic reaction in cellular respiration is catalyzed by a specific enzyme. 2. As a metabolite is oxidized, NAD + (nicotinamide adenine dinucleotide) accepts two electrons and a hydrogen ion (H + ); this results in NADH + H + . 3. Electrons received by NAD + and FAD are high-energy electrons and are usually carried to the electron transport chain. 4. NAD + is a coenzyme of oxidation-reduction since it both accepts and gives up electrons; thus, NAD + is sometimes called a redox coenzyme 5. Only a small amount of NAD + is needed in cells because each NAD + molecule is used repeatedly. 6. FAD coenzyme of oxidation-reduction can replace NAD + ; FAD accepts two electrons and two hydrogen ions to become FADH 2 . C. Phases of Cellular Respiration 1. Cellular respiration includes four phases: a. Glycolysis is the breakdown of glucose in the cytoplasm into two molecules of pyruvate. i. Enough energy is released for an immediate yield of two ATP. ii. Glycolysis takes place outside the mitochondria and does not utilize oxygen; it is therefore an anaerobic process.
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b. In the preparatory (prep) reaction , pyruvate enters a mitochondrion and is oxidized to a two-carbon acetyl group and CO 2 is removed; this reaction occurs twice per glucose molecule. c. The citric acid cycle : i. occurs in the matrix of the mitochondrion and produces NADH and FADH 2 ; ii. is a series of reactions that gives off CO 2 and produces one ATP; iii. turns twice because two acetyl-CoA molecules enter the cycle per glucose molecule; iv. produces two immediate ATP molecules per glucose molecule. d.
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Biology Chapter 8 - 8.1 Cellular Respiration 1 Cellular...

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