2. Metabolism Continued

3. Aerobic Respiration Principle means of synthesizing ATP in animals Three stages 1.Glycolysis (cytosol) glucose  pyruvate 2.Krebs Cycle (mitochondria) formation of electron carriers and CO 2 3.Oxidative Phosphorylation (mitochondria) electron carriers create proton gradient used to generate ATP

4. 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 O 2 consumed) of 3 ATP per NADH and 2 ATP per FADH 2 –10 NADH  3 = 30 ATP –2 FADH 2  2 = 4 ATP Maximum yield = 38 ATP per glucose

5. How Much ATP is REALLY Generated? Less than 38 ATP (~30 in humans) Most cells transfer electrons from cytosolic NADH to FADH 2 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 FADH 2

6. 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

7. 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

8. Other Ways of Generating ATP Phosphagen Usage –Molecules store high energy phosphate groups Arginine phosphate (invertebrates) Creatine phosphate (vertebrates) –Transfer PO 4 groups to ADP as ATP/ADP ratio lowers –Take up PO 4 groups from ATP as ATP/ADP ratio increases

9. 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 O 2 if intracellular P O2 drops

10. Metabolism in Low O 2 Metabolism is independent of O 2 concentrations to some degree (O 2 regulation) Low O 2 may affect metabolism (O 2 conformity)

11. Responses to Low O 2 Increase ability to uptake O 2 Increased tolerance of hypoxia –Reliance on anaerobic metabolism

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

13. 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

14. 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

15. 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

16. Energetic Cost of Transport COT = O 2 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

17. 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

18. Flight U-shaped relationship between O 2 consumption and flight speed –O 2 consumption minimized at a certain flight velocity –  O 2 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

19. Cost of Flight Speed of lowest cost of transport  speed of minimum VO 2 e.g. parakeets – min VO 2 at 35 kph –Min COT (V O2 *kg -1 *km -1 ) at 40 kph

20. 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  velocity 2

21. 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