Aerobic and Anaerobic Forms of Metabolism

1. Aerobic and Anaerobic Forms of Metabolism

2. Exercise and energy • Energy is needed for all exercises • ATP, the most important molecule carrying energy, can be stored in small amount but is not exchange à need to be made on a constant

3. Mechanisms of ATP production • All 3 major categories of food can be degraded through these processes • 4 major sets of reactions in aerobic catalysis: • Glycolysis • Krebs cycle • Electron transport chain (ETC) • Oxidative phosphorylation

5. Electron transport chain

6. Net results from glycolysis and Krebs cycle • Glycolysis: 1 glucose + 2 ADP + 2 NAD + 2 P à 2 pyruvic acid + 2 ATP + 2 NADH+ + 2 H2O • Krebs cycle 2 pyruvic acid + 6 NAD + 2 FAD à 8 NADH+ + 2 FADH + 2 GTP + 6CO2 Electron Transport Chain (ETC) NADH+ + ADP + ½ O2 à NAD + 3 ATP + H2O FADH + ADP + ½ O2 à FAD + 2 ATP + H20 Oxidative phosphorylation ADP + Pi à ATP

7. P/O ratio = expresses the yield of ATP formation by oxidative phosphorylation (OP) per atom of O2 reduced to H2O • If complete coupling between ETC and OP: 3 ATP formed • If completely uncoupled: 0 ATP • During uncoupling, NAD and FAD are formed but instead of ATPs formed, heat is produced à used by mammals to produce heat during cold seasons and a mean to control weight. • Max of 34 ATPs from OP • Additional ATPs from substrate phosphorylation • Total ATPs = 40-2 = 38

8. Consequences of O2 deficiency • Lack of O2à ETC becomes fully reduced and is blocked à no ATP, no NAD and FAD regenerations • Some tissues can generate some ATP without O2 à anaerobic glycolysis • Formation of lactic acid and regeneration of NAD • Muscles can do that, not brain • Net production of 2 ATP / glucose

9. Mammalian brains use ATP much faster than can be produced anaerobically à these brains must have O2! • If no ATP à Na+ K+ pump, Ca++ pump do not function à neurons destroyed

10. Fates of catabolic end-products • Aerobic glycolysis: • Glucose is fully degraded à CO2 + H2O production à respiration • Anaerobic end-products: lactic acid: • molecule still rich in energyà wasteful to eliminate • But too toxic to retain in large amount • Anaerobic conditions are usually short à possibility to use lactic acid later

11. Vertebrates can metabolize lactic acid • Gluconeogenesis (6 ATP + O2 used) • Or full oxidation to CO2 + H2O and 36 ATP formation

12. Steady / Non-steady state • Steady-state mechanism of ATP production if: • 1. ATP produced as fast as it is used • 2. uses raw materials no faster than it is replenished • 3. chemical by-products voided as fast as produced • 4. cell remains in homeostatic equilibrium • Non-steady state: • ATP is consumed faster than it is produced • Wastes are accumulating faster than they can be eliminated • Ex: phosphagen system

13. Patterns of Energy Use • Sustained or short burst • Mild or Strenuous

14. Patterns of Energy Use During sustained exercise: - ATP is consumed - when the ATP stores are down, use of the phosphagen compounds - creatinine phosphate found in vertebrate muscle, - arginine phosphate in invertebrates Then, ATP is aerobically synthesized from fatty-acids and/or glucose • Muscles are especially geared to use fatty-acids à derived from fat (triglycerides through b-oxidation in the liver) • Glucose is used or synthesized from glycogen reserves

15. Aerobic ATP synthesis needs….. O2! • If the exercise is strenuous, the O2 store might not be adequate to support this synthesis • Then, the body has no choice but to turn to anaerobic glycolysis à less efficient ATP synthesis + lactic acid accumulation

16. Muscle fatigue and return to resting state • Many causes: • Lack of O2 in the muscle or in the blood • Lack of glucose or glycogen store • Accumulation of lactic acid • Accumulation of calcium ions in inappropriate cell compartments

17. Mechanisms of ATP production and use

18. Muscle fiber types • Slow oxidative (SO) • Rich in mitochondria • High level of enzymes involvd in oxidative pathways • Muscle rich in blood vessels and myoglobin à red color • Fast glycolytic (FG) • Rich in ATPase • Less blood vessels, mitochondria à white color

21. Uses of energy in animals ?? • Birds during migration • Lobsters during escape behavior (short burst of tail muscle contraction) • Salmons during upstream migration • Antelope during escape run

22. Response to decreased O2 in environment • Shut-down metabolism à dormancy (brine-shrimp embryo • Diving animals: dive long enough to use O2 store and/or use anaerobic glycolysis à lactic acid use à must be eliminated prior to next dive

23. Some animals (diving turtles) can sustain long periods without oxygen: • Uses metabolic depression to maintain brain tissue integrity • Turtles become comatose, accumulate large store of lactic acid

24. ATP synthesis under reduced O2 availability • O2 regulation: steady rate of O2 consumption and ATP synthesis despite changing level of O2. possible only over a certain range of [O2] • O2 conformity: O2 rate of consumption falls with O2 in environment

25. Water-breathing anaerobes • Uncommon: some clams, mussels, worms, some goldfishes à buried in marsh sediments (no O2) • Strategy to survive anoxia: • metabolic depression • ATP synthesis through acetic, succinic, proprionic acids and alanine synthesis à excreted in environment à less acidity

26. Anaerobiosis in goldfish and crucian carp • These fishes synthesize LDH à lactic acid formation • Muscles can convert lactic acid to ethanol + CO2 • Consequences?