CH9 - CHAPTER 9 Overview: Life Is Work Living cells require...

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1 CHAPTER 9 Overview: Life Is Work • Living cells require energy from outside sources • Some animals, such as the giant panda, obtain energy by eating plants, and some animals feed on other organisms that eat plants • Energy flows into an ecosystem as sunlight and leaves as heat • Photosynthesis generates O 2 and organic molecules, which are used in cellular respiration • Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work Fig. 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2 O Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Heat energy ATP
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2 CATABOLIC PATHWAYS yield energy by oxidizing organic fuels • Several processes are central to cellular respiration and related pathways Fermentation: a partial degradation of sugars that occurs without O 2 Aerobic respiration: consumption of organic molecules and O 2 to yield ATP Anaerobic respiration: similar to aerobic respiration but consumes compounds other than O 2 Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration • Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose: C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + Energy (ATP + heat) Catabolic Pathways and Production of ATP Redox Reactions: Oxidation and Reduction • The transfer of electrons during chemical reactions releases energy stored in organic molecules • This released energy is ultimately used to synthesize ATP
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3 The Principle of Redox • Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions In oxidation , a substance loses electrons, or is oxidized • In reduction , a substance gains electrons, or is reduced ( the amount of positive charge is reduced ) Fig. 9-UN1 becomes oxidized (loses electron) becomes reduced (gains electron) • The electron donor is called the REDUCING AGENT • The electron receptor is called the OXIDIZING AGENT
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4 Oxidation of Organic Fuel Molecules During Cellular Respiration • During cellular respiration, the fuel (such as glucose) is oxidized, and O 2 is reduced: Stepwise Energy Harvest via NAD + and the Electron Transport Chain • In cellular respiration, glucose and other organic molecules are broken down in a series of steps • Electrons from organic compounds are usually first transferred to NAD + , a coenzyme • As an electron acceptor, NAD + functions as an OXIDIZING AGENT during cellular respiration • Each NADH (the reduced form of NAD + ) represents stored energy that is tapped to synthesize ATP Fig. 9-UN4 Dehydrogenase
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5 Fig. 9-4 Dehydrog enase Reduction of NAD + Oxidation of NADH 2 e + 2 H + 2 e + H + NAD + + 2[H] NADH + H + H + Nicotina mide (oxidized form) Nicotina mide (reduced form) • NADH passes the electrons to the electron transport chain
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CH9 - CHAPTER 9 Overview: Life Is Work Living cells require...

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