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Biochemistry of Respiration

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BIOL 200
Mary Silas

Biochemistry of Respiration  Oxidative breakdown of organic molecules to store energy as ATP  Animals and plants respire; FAD and NAD are coenzymes Aerobic respiration  C6H12O6 + 6O2 → 6CO2 + 6H2O + energy  Complete oxidation of an organic substrate to CO2 and H2O using free O2  Production of CO2, NADH + H+ and FADH + H+, 38ATP 1) Glycolysis → cytoplasm  Glucose enters cell by facilitated diffusion  ATP activates glucose to produce 2 unstable compounds  Substrate-level phosphorylation produces 4ATP  Net yield of 2ATP and 2reducedNAD per glucose molecule 2) Link reaction → matrix of mitochondria  Pyruvate enters matrix of mitochondrion for further reaction  Net yield of 2reducedNADH per glucose 3) Krebs cycle → matrix of mitochondria  Citrate is gradually broken down to re-form oxaloacetate  Substrate-level phosphorylation forms 2ATP  Removal of hydrogen from respiratory substrate  Net yield of 2ATP, 2reducedFADH, 6reducedNADH per glucose 4) Electron Transport Chain ETC → inner membrane/cristae of mitochondria  Reduced coenzymes arrive at ETC  Split into coenzyme + 2H+ + 2e- by hydrogen carriers  2e- are transferred to electron carriers (cytochrome)  Pass down ETC by redox reaction and release energy as they go  Energy produces ATP by oxidative phosphorylation  Final electron acceptor 1/2O2 is reduced by 2H+ and 2e- to produce H2O  Net yield of 34ATP (30NADH, 4FADH) per glucose  //Cytochromes are iron-containing proteins → cytochrome a3 also contains copper and is irreversibly damaged by cyanide IMG 5-14-8 Anaerobic respiration (fermentation)  Substrate-level phosphorylation: 2ADP + 2Pi → 2ATP directly by enzymes in glycolysis  No O2 to accept electrons from NADH + H+ → no Krebs cycle or ETC  NADH + H+ reduces (gives off H+ ions to) pyruvate to produce o Lactate C3 in animal cells → can be re-oxidised o Ethanol C2 in yeast cells → irreversible, CO2(g) lost  Regenerates NAD  NAD can be re-used to oxidise more RS/allows glycolysis to contin
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