Chapter 9 - Chapter 9 - Living cells require transfusions...

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Chapter 9 - Living cells require transfusions of energy from outside sources to perform their many tasks—for example, assembling polymers, pumping substances across membranes, moving, and reproducing. - Energy flows into an ecosystem as sunlight and exits as heat; in contrast, the chemical elements essential to life are recycled. 9.1 – Catabolic pathways yield energy by oxidizing organic fuels - Compounds that can participate in exergonic reactions can act as fuels. - One catabolic process, fermentation , is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen. - However, the most prevalent and efficient catabolic pathway is aerobic respiration , in which oxygen is consumed as a reactant along with the organic fuel. - Some prokaryotes use substances other than oxygen as reactants in a similar process that harvests chemical energy without oxygen; this process is called anaerobic respiration . - Technically, the term cellular respiration includes both aerobic and anaerobic processes. However, it originated as a synonym for aerobic respiration because of the relationship of that process to organismal respiration, in which an animal breathes in oxygen. Thus, cellular respiration is often used to refer to the aerobic process. - The breakdown of glucose is exergonic. - The transfer of electrons in a chemical reaction is known as oxidation-reduction reactions, or redox reactions for short. - In a redox reaction, the loss of electrons from one substance is called oxidation , and the addition of electrons to another substance is known as reduction . - Reducing agent – The electron donor - Oxidizing agent – The electron acceptor. - Xe- (oxidized)+ Y (reduced) => X (reducing agent) + Ye- (oxidizing agent) - NAD + - - Nicotinamide adenine dinucleotide, a coenzyme that cycles easily between oxidized (NAD+) and reduced (NADH) states, thus acting as an electron carrier - An electron transport chain consists of a number of molecules, mostly proteins, built into the inner membrane of the mitochondria of eukaryotic cells and the plasma membrane of aerobically respiring prokaryotes. - In summary, during cellular respiration, most electrons travel the following “downhill” route: glucose => NADH => electron transport chain => oxygen. - Glycolysis, which occurs in the cytosol, begins the degradation process by breaking glucose into two molecules of a compound called pyruvate. - In eukaryotes, pyruvate enters the mitochondrion and is oxidized to a compound called acetyl CoA, which enters the citric acid cycle. - The energy released at each step of the chain is stored in a form the mitochondrion (prokaryotic cell) can use to make ATP from ADP. This mode of ATP synthesis is called oxidative phosphorylation because it is powered by the redox reactions of the electron transport chain. - Oxidative phosphorylation accounts for almost 90% of the ATP generated by
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This note was uploaded on 03/06/2012 for the course ECON 200 Bones taught by Professor Dr.elwonger during the Winter '12 term at Ohio State.

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Chapter 9 - Chapter 9 - Living cells require transfusions...

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