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Metabolism

Metabolism. Continued. Aerobic Respiration. Principle means of synthesizing ATP in animals Three stages Glycolysis (cytosol) glucose  pyruvate Krebs Cycle (mitochondria) formation of electron carriers and CO 2 Oxidative Phosphorylation (mitochondria)

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Metabolism

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  1. Metabolism Continued

  2. Aerobic Respiration • Principle means of synthesizing ATP in animals • Three stages • Glycolysis (cytosol) • glucose  pyruvate • Krebs Cycle(mitochondria) • formation of electron carriers and CO2 • Oxidative Phosphorylation(mitochondria) • electron carriers create proton gradient used to generate ATP Figs 6.1-6.2

  3. How Much ATP Can Be Generated? • 4 ATP gross (2 ATP net) in glycolysis • 2 GTP in the Krebs cycle • Theoretical maximum P/O ratios (#ATP per molecule of O2 consumed) of 3 ATP per NADH and 2 ATP per FADH2 • 10 NADH  3 = 30 ATP • 2 FADH2  2 = 4 ATP • Maximum yield = 38 ATP per glucose

  4. How Much ATP is REALLY Generated? • Less than 38 ATP (~30 in humans) • Most cells transfer electrons from cytosolic NADH to FADH2 in the mitochondrial matrix • Lose 2 ATP • Proton leakage across inner mitochondrial membrane • Lower actual P/O ratios: ~2.5 for NADH and 1.5 for FADH2 Box 6.1

  5. Other Ways of Generating ATP • Anaerobic Fermentation • Glycolysis used to generate ATP • NAD+ reduced to NADH • Must oxidize NADH back to NAD+ • Reduce pyruvate into lactate • Aquatic invertebrates • more complex pathways • Involve Krebs cycle reactions and truncated electron transport activity Fig 6.3

  6. Anaerobic Metabolism • Problems • Low energy yield • Acid production affects cell/body pH • What do you do with it? • Reuse it • Lactate used by liver to regenerate glycogen (Cori cycle) • Get rid of it • Carp convert lactate to ethanol and release it through gills • Aquatic invertebrates release various organic molecules Figs 6.4, 6.13

  7. Other Ways of Generating ATP • Phosphagen Usage • Molecules store high energy phosphate groups • Arginine phosphate (invertebrates) • Creatine phosphate (vertebrates) • Transfer PO4 groups to ADP as ATP/ADP ratio lowers • Take up PO4 groups from ATP as ATP/ADP ratio increases Fig 6.5

  8. Other Ways of Generating ATP • Stored Oxygen • Gas-binding pigments in tissues (e.g., myoglobin) can provide a reservoir of oxygen for aerobic respiration • Release O2 if intracellular PO2 drops Fig 22.7a

  9. Metabolism in Low O2 • Metabolism is independent of O2 concentrations to some degree (O2 regulation) • Low O2 may affect metabolism (O2 conformity) Fig 6.12a

  10. Responses to Low O2 • Increase ability to uptake O2 • Increased tolerance of hypoxia • Reliance on anaerobic metabolism Fig 6.12b

  11. Metabolism and Locomotion • Types of Locomotion • Cursorial • Swimming • Flight • How do these compare in energetic efficiency?

  12. Factors Influencing Cost of Locomotion • Support for body weight provided by the media • e.g. water – high support of body weight • e.g. air – low support for body weight • Resistance to movement • Dependent on density and viscosity of media • e.g. water – high resistance • e.g. air – lower resistance

  13. Cursorial Movement • Use limbs as levels to push against solid substrate • More energy required to run at higher velocities • Generally linear increase • Curvilinear at high speeds

  14. Cursorial Movement • Different patterns of limb movement (gaits) most efficient at different speeds • With increased speed, gait transitions occur • E.g. humans: walk  run • E.g. horses: walk  trot  gallop

  15. Energetic Cost of Transport • COT = O2 consumed/distance traveled • Certain gaits are most efficient at a set speed • E.g. horses: run at speeds in each gait that minimize cost of transport

  16. Cost of Transport and Body Size • Small animals tend to have greater increases in energy expenditure with increasing velocity • Energetic cost of transport higher for smaller animals • Similar relationship among diverse animal taxa Fig 7.4

  17. Flight • U-shaped relationship between O2 consumption and flight speed • O2 consumption minimized at a certain flight velocity • O2 consumption at higher AND lower speeds • Wing beats generate thrust and lift • Bernoulli effect •  speed,  lift • At low speeds, more lift has to be generated by downward beating of wings Fig 7.5

  18. Cost of Flight • Speed of lowest cost of transport  speed of minimum VO2 • e.g. parakeets – min VO2 at 35 kph • Min COT (VO2*kg-1*km-1) at 40 kph Fig 7.6

  19. Swimming • Dense, viscous medium • Supports body mass • Generates high levels of drag • Force exerted in opposite direction of movement • Affected by media density, shape, size and velocity •  w/ density and viscosity •  with streamlining • Drag  surface area • Drag  velocity2 Fig 7.3

  20. Which is the Most Efficient? • Swimming has the least expensive COT • Low speed, but no need for body support • Flight has the next least expensive COT • High energy input required, but high speeds and low drag increase efficiency Fig 7.7

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