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Tricarboxcylic acid cycle

Tricarboxcylic acid cycle. Anaerobic, cell membrane or mitochondria Each pyruvate gives up its carbon as CO 2 6 total Oxaloacetate is regenerated with every turn Pick up molecule 2 ATP are produced Substrate level phosphorylation. TCA cycle occurs twice per glucose.

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Tricarboxcylic acid cycle

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  1. Tricarboxcylic acid cycle • Anaerobic, cell membrane or mitochondria • Each pyruvate gives up its carbon as CO2 • 6 total • Oxaloacetate is regenerated with every turn • Pick up molecule • 2 ATP are produced • Substrate level phosphorylation

  2. TCA cycle occurs twice per glucose • Net yield of product per glucose molecule: • 6 CO2 • 2 ATP • 8 NADH = 3 ATP • 2 FADH2 = 2 ATP

  3. ELECTRON TRANPORT • Aerobic or anaerobic • Final electron acceptor: • aerobic respiration - oxygen • anaerobic respiration - CO2, NO3-, SO42 • Inner mitochondrial membrane or plasma membrane • Electrons move down chain and set up H+ gradient • drives chemiosmosis

  4. Electron transport systems consist of separate protein complexes Oxidative Phosphorylation – series of redox reactions creating a stepwise release of energy

  5. Electron transport chains often branch

  6. Proton Motive Force generated by chemical and electrical gradient Proton flow across membrane is exerogonic

  7. Using the PMF, ATP synthesis is catalyzed by ATP synthase (ATPase), through a process called chemiosmosis

  8. Complete Aerobic Catabolism of Glucose • C6H12O6 + 6O2 + 36ADP + 36P → 6CO2 + 6H2O + 36ATP • (eukaryote) • C6H12O6 + 6O2 + 38ADP + 38P → 6CO2 + 6H2O + 38ATP • (prokaryote) Typical net energy yield: 36 ATP for eukaryotes 38 ATP for prokaryotes By-products of aerobic respiration are H2O and CO2

  9. Substrate-Level Phosphorylation • 2 ATP (net gain Glycolysis) • 2 ATP (TCA cycle) • 4 Total from substrate-level phosphorylation • Oxidative Phosphorylation • 6 ATP (NADH Glycolysis) • 28 ATP (NADH/FADH2 TCA cycle) • 34 total from oxidative phosphorylation • Total ATP gain ~ 36 to 38

  10. Anaerobic Respiration Many compounds can serve as terminal electron acceptors

  11. E.coli • Nitrate reduction • N03- + 2e- + 2H+ N02-+ H20 • Paracoccus, Bacillus and Pseudomonas • Denitrification • N03- N02- NO N2O N2

  12. Nitrate reduction and ammonification Denitrification in Paracoccus

  13. Desulfovibrio • Reduce sulfate • acetate + SO4-2 + 3H+ 2CO2 + H2S + 2H2O • Archaea • Methanogens that reduce carbonate • HC03- + 4H2 + H+ CH4 + 3H2O

  14. Common • Not associated with any one phylogenetic group • Except methanogenesis • Involves: • membrane system • generation of ion gradient • formation of ATP via ATP synthase

  15. Less efficient than aerobic respiration • Electron acceptors have less positive reduction potentials than oxygen • lower energy yield

  16. Fermentation • Used by organisms that can’t respire • lack of suitable inorganic electron acceptor or lack of electron transport chain • Anaerobic; Occurs in the cytoplasm

  17. Partial oxidation of substrate • NADH oxidized back to NAD+ • Uses organic compound as terminal electron acceptor • Typically pyruvate or derivative • NO oxidative phosphorylation so ATP yield is low

  18. Lactic acid fermentation • pyruvate reduced to lactate • pyruvate accepts electrons and protons from NADH

  19. Alcohol fermentation • pyruvate decarboxylated to form acetaldehyde • NADH transfers electrons and protons to acetaldehyde reducing it to ethanol

  20. Catabolism of Other Organic Compounds • Carbohydrates are the main energy source • glucose • Microbes may also utilize lipids and proteins • Both must be broken down into their individual components • Each component is oxidized separately

  21. Lipid Catabolism • Lipases • Fatty acids and glycerol • Fatty acid converted into acetyl CoA, enters TCA cycle • Glycerol converted into DHAP, enters glycolysis

  22. Protein Catabolism • Proteases • Amino acids • can NOT be catabolized directly • transamination • decarboxylation • dehydrogenation

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