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Unformatted text preview: Chapter 9: Cellular Respiration Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels. Catabolic Pathways and the Production of ATP o Fermentation is a catabolic process that involves the partial degradation of sugars without the use of oxygen. o Cellular respiration can be summarized as follows: Organic compounds + oxygen carbon dioxide + water + energy C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy (ATP + heat) The breakdown of glucose is exergonic, having a free energy change (G) of about -686 kcal per mole of glucose. Spontaneous reaction (can occur without input of energy) Redox Reactions: Oxidation and Reduction o The Principle of Redox Oxidation : loss of an electron (removal of one hydrogen) Reduction : gain of an electron (addition of one hydrogen)----------------- becomes oxidized (lose e-) | | Xe- + Y X + Ye- | |--------------- becomes reduced (gain e-) Reducing agent : X is the electron donor; reduces Y, which accepts the donated electron. Oxidizing agent : Y is the electron acceptor; oxidizes X by removing its electron.----------------- becomes oxidized (lose e-) | | Na + Cl Na + + Cl- | |--------------- becomes reduced (gain e-) Transfer of an electron from Na to Cl These two are collectively called a redox reaction : electrons go from higher energy levels to lower energy levelstransfer of one or more electrons from one reactant to another. o Oxidation of Organic Fuel Molecules During Cellular Respiration----------------------- becomes oxidized (lose e-) | | C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + Energy | |--------------------- becomes reduced (gain e-) Glucose is oxidized and oxygen is reduced. By oxidizing glucose, respiration liberates stored energy from glucose and makes it available for ATP synthesis. Energy is released because of the change in the covalent status. o Stepwise Energy Harvest via NAD+ and the Electron Transport Chain Hydrogen cannot be immediately put on the oxygenthere would be an explosion! Instead---stepwise process. Electron carriers are used to pass the electrons (H) slowly to the oxygen. In this stepwise process, a little energy is given off at each step. Hydrogen atoms are usually passed first to a coenzyme called NAD+ (nicotinamide adenine dinucleotide)dehydrogenase enzymes remove a pair of H atoms (two electrons and two protons) from the substrate (e.g. sugar), thereby oxidizing it. Then, the enzyme delivers two electrons and one proton to NAD+ and it becomes NADH + H + (the other proton is released as a hydrogen ion into the surroundings). FAD (flavin adenine dinucleotide) FADH 2 (dehydrogenase takes two hydrogen) Substrate level phosphorylation : the direct coupling of a step in a catabolic reaction to make ATP by enzymatic transfer of the phosphate to ADP Phosphorylation: adding phosphate group Enzymes: An enzyme holds substrate with phosphorus enzyme can also hold ADP...
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- Spring '08
- Cellular Respiration