How Cells Harvest Energy 7 - Respiration-Organisms can be...

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Respiration -Organisms can be classified based on how they obtain energy: - Autotrophs -Able to produce their own organic molecules through photosynthesis - Heterotrophs - Live on organic compounds produced by other organisms -All organisms use cellular respiration to extract energy from organic molecules Cellular Respiration -Series of reactions - Oxidized -> loss of electrons - Reduced -> gain of electron - Dehydrogenation -> lost electrons are accompanied by protons - A hydrogen atom is lost (1 electron, 1 proton) Redox -Electrons carry energy from one molecule to another - Nicotinamide adenosine dinucleotide (NAD+) - An electron carrier - NAD+ accepts 2 electrons and 1 proton to become NADH - Reaction is reversible -In overall cellular energy harvest… - Dozens of redox reactions take place - Number of electron acceptors including NAD+ -In the end, high-energy electrons from initial chemical bonds have lost much of their energy -Transferred to a final electron acceptor - Aerobic Respiration - Final electron receptor is oxygen (O2) - Anaerobic Respiration - Final electron acceptor is an inorganic molecule (not O2) - Fermentation - Final electron acceptor is an organic molecule Aerobic Respiration -Free energy = -686 kcal/mol of glucose -Free energy can be even higher than this in a cell -This large amount of energy must be released in small steps rather than all at once Electron Carriers -Many types of carriers used (Soluble, Membrane-bound, Move within membrane) -All carriers can be easily oxidized and reduced -Some carry just electrons, some electrons and protons -NAD+ acquires 2 electrons and a proton to become NADH
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ATP -Cells use ATP to drive endergonic reactions - G (free energy) = -7.3 kcal/mol
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