respiration

• what are the 4 stages of aerobic respiration glycolysis link reaction krebs cycle oxidative phosphorylation
• glycolysis products net 2 ATP 2 reduced NAD 2 pyruvate
• glycolysis 1. glucose phosphorylated to glucose phosphate then hexose bisphosphate by hydrolysis of 2 ATP 2. hexose bisphosphate hydrolysed to 2 triose phosphate (TP) 3. each TP loses 2H+ to reduce 1 NAD 4. for each TP, 2 ATP synthesised from ADP + Pi 5. forms 2 pyruvate
• link reaction 1. pyruvate loses 1 CO2 + 2H+ to form acetate + reduce 1 NAD 2. acetate combines with coenzyme A to form acetylcoenzyme A
• link reaction products 1 acetyl coenzyme A 1 reduced NAD 1 CO2
• krebs cycle 1. acetyl CoA combines with 4C oxaloacetate to form 6C citrate 2. coenzyme A recycled into link reaction 3. citrate loses 1 CO2 4. 1 NAD reduced 5. 5C intermediate formed 6. loses 1 CO2 7. 1 NAD reduced 8. forms 4C intermediate 9. 1 ATP formed by substrate-level phosphorylation 10. 1 FAD reduced 11. 1 NAD reduced 12. 4C oxaloacetate formed
• krebs cycle products 2 CO2 1 coenzyme A 3 reduced NAD 1 reduced FAD 1 ATP
• how much ATP per reduced FAD 1.5
• how much ATP per reduced NAD 2.5
• why is the krebs cycle important in the cells of organisms 1. breaks down macromolecules into smaller ones 2. produces H atoms that are carried by NAD to the ETC and provide energy for oxidative phosphorylation 3. regenerates oxaloacetate which would otherwise accumulate 4. source of intermediate compounds used by cells in manufacture of other important substances e.g. fatty acids, amino acids, chlorophyll
• oxidative phosphorylation (electron transport chain) 1. in matrix of mitochondria, reduced NAD oxidised to NAD, 2H released split into 2H+ and 2e- 2. e- move down ETC in mitochondrial membrane in series of redox reactions, releasing small amount of energy 3. energy used to actively pump H+ through electron carriers into intermembrane space, establishing concentration + electrochemical gradient of H+; high in intermembrane space, low in matrix 4. H+ passively move through ATP synthase channels in membrane down conc + EC gradient 5. stimulates ATP synthase to catalyse 2ADP + 2Pi -> 2ATP per H+ via oxidative phosphorylation 6. 2e- which leave ETC combine with 1/2 O2 and 2H+ to form 2H2O (oxygen acts as final e- acceptor)
• why is anaerobic respiration necessary krebs cycle + ETC cannot continue as all NAD + FAD will become reduced leaves only glycolysis as potential source of ATP for glycolysis to continue, hydrogen must be released from reduced NAD to regenerate NAD to take up hydrogen newly produced from glycolysis
• why is anaerobic respiration unsustainable lactic acid denatures enzymes
• anaerobic respiration in plants + some microorganisms pyruvate loses a CO2 and accepts hydrogen from reduced NAD to produce ethanol pyruvate + reduced NAD -> ethanol + CO2 + NAD
• how is anaerobic respiration of yeast exploited by humans

  in brewing, ethanol is the important product yeast grown in anaerobic conditions in which it ferments natural carbohydrates in plant products into ethanol
• anaerobic respiration in animals

  • pyruvate takes up the 2 hydrogen atoms from the reduced NAD produced in glycolysis to form lactate
  • pyruvate + reduced NAD -> lactate + NAD
• what happens to the lactate once oxygen is available

  • oxidised back to pyruvate
  • can then be either further oxidised to release energy or taken to the liver and converted into glycogen
• oxygen debt

  the amount of oxygen required after physical exercise to convert accumulated lactate to glucose
• when does oxygen debt occur

  when oxygen is used up more rapidly than it can be supplied