10-23-06 (16) Respiration

10-23-06 (16) Respiration - Cellular Respiration October...

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Unformatted text preview: Cellular Respiration October 23, 2006 Life is Work Living cells require energy from outside sources to perform their many tasks Energy Flow and Chemical Recycling Energy flows into an ecosystem as sunlight and leaves as heat Chemical elements are recycled Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Heat energ y Figure 9.2 Catabolic Pathways Release stored energy by breaking down complex molecules to simpler products Fermentation making energy without oxygen; partial dehydration of sugars without energy Cellular respiration Breakdown of sugars with help of oxygen Most efficient catabolic pathway Catabolic Pathways Cellular respiration C 6 H 12 O 6 + 6 O 2 6 CO 2 +6 H 2 0 +Energy G = -686 kcal/mol Catabolic Pathways Yield energy by oxidizing organic fuels Based on the transfer of electrons during chemical reactions This energy then used to synthesize ATP Redox Reactions: Oxidation and Reduction Electron transfers from one reactant to another are oxidation-reduction reactions Oxidation Reduction Redox Na + Cl Na + + Cl becomes oxidized (loses electron) becomes reduced (gains electron) X e- + Y X + Y e- becomes oxidized (loses electron) becomes reduced (gains electron) Redox Some redox reactions do not completely exchange electrons Change the degree of electron sharing in covalent bonds Redox CH 4 H H H H C O O O O O C H H Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water + 2O 2 CO 2 + Energy + 2 H 2 O becomes oxidized becomes reduced Reactants Products Figure 9.3 Oxidation of Organic Fuel Molecules During cellular respiration glucose is oxidized and oxygen is reduced C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy becomes oxidized becomes reduced Stepwise Energy Harvesting Cellular respiration oxidizes glucose in a series of steps NAD + Electron transport chain NAD + NAD + H O O O O O O O O O O P P CH 2 CH 2 HO OH H H HO OH HO H H N + C NH 2 H N H NH 2 N N Nicotinamide (oxidized form) NH 2 + 2[H] (from food) Dehydrogenase Reduction of NAD + Oxidation of NADH 2 e + 2 H + 2 e + H + NADH O H H N C + Nicotinamide (reduced form) N Figure 9.4 NADH The reduced form of NAD + Represents stored energy that can be tapped to make ATP when electrons fall down to oxygen Passes electrons to the electron transport chain Electron Transport Chain If electron transfer is not stepwise a large release of energy occurs Reaction of hydrogen and oxygen to form water Free energy, G H 2 O Explosive release of heat and light energy Figure 9.5 A H 2 + 1 / 2 O 2 Electron Transport Chain Passes electrons in a series of steps instead of in one explosive reaction Uses the energy from the electron transfer to form ATP Electron Transport Chain 2 H 1 / 2 O 2 (from food via NADH) 2 H + + 2 e 2 H + 2 e H 2 O 1 / 2 O...
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10-23-06 (16) Respiration - Cellular Respiration October...

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