CH 7 - Ch.07- How cells harvest energy BIO 1610 autotrophs:...

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1 Ch.07- How cells harvest energy BIO 1610 autotrophs : are able to produce their own organic molecules through photosynthesis heterotrophs : live on organic compounds organic compounds produced by other organisms All organisms use cellular respiration to extract energy from organic molecules. Cellular respiration is a series of reactions that: -are oxidations – loss of electrons -are also Cellular respiration 2 dehydrogenations – lost electrons are accompanied by hydrogen Æ what is actually lost is a hydrogen atom (1 electron, 1 proton). Energy efficiency of cellular respiration ~32% Cellular respiration is the complete oxidation of glucose Digestive enzymes Glycolysis Oxidation ATP produced is transported to the cytosol to be used NAD+ and NADH serve as electron shuttles during cellular respiration 4 NAD+ is used in harvesting energy from glucose molecules in a series of gradual steps in the cytoplasm -NAD accepts 2 electrons and 1 proton to become NADH -the reaction is reversible. Redox reactions Dehydrogenase enzymes strip two hydrogen atoms from the fuel, pass two electrons and one proton to NAD+ and release H+. H-C-OH + NAD+ Æ C=O + NADH + H+ 5 Glucose and other fuels are broken down gradually in a series of steps, each catalyzed by a specific enzyme. Fig. 9.5
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2 Electrons are shuttled through electron carriers to a final electron acceptor. aerobic respiration : final electron receptor is oxygen (O 2 ) anaerobic respiration : final electron acceptor is an inorganic molecule (not O 2 ) e.g. nitrate, sulfate fumarate, malate fermentation : final electron acceptor is an organic molecule. Electrons disposed in an electron sink (alcohols, organic acids). Electrons are transferred back to the original substrate (pyruvate) Cellular respiration shuttles electrons 7 Δ G = -686kcal/mol of glucose Δ G can be even higher Aerobic respiration C 6 H 12 O 6 + 6O 2 Æ 6CO 2 + 6H 2 O + Energy (ATP + heat) 8 than this in a cell This large amount of energy must be released in small steps rather than all at once. Oxidative phosphorylation produces almost 90% of the ATP generated by respiration. An enzyme transfers a phosphate group from an organic molecule (the substrate) to ADP, forming ATP. Some ATP is also generated in glycolysis and the Krebs cycle by substrate-level phosphorylation . Only 4 ATP produced by respiration of glucose are derived from substrate-level phosphorylation. Both glycolysis and the citric acid cycle Can generate ATP by substrate-level phosphorylation Enzyme Enzyme ATP ADP Product Substrate P + The complete oxidation of glucose proceeds in stages : 1. glycolysis 2. pyruvate oxidation 3. Krebs cycle 12
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3 The transfer of e- from NADH to O2 drive the synthesis of 2.5 molecules of ATP. Transfer of e- from FADH2 to O2
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CH 7 - Ch.07- How cells harvest energy BIO 1610 autotrophs:...

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