1 / 52

Chapter 2

Chapter 2. Fuel for Exercise: Bioenergetics and Muscle Metabolism. Chapter 2 Overview. Substrates: fuel for exercise Controlling the rate of energy production Stored energy: high-energy phosphates Bioenergetics: basic energy systems Interaction among energy systems. Terminology.

ishana
Download Presentation

Chapter 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 2 • Fuel for Exercise:Bioenergetics and Muscle Metabolism

  2. Chapter 2 Overview • Substrates: fuel for exercise • Controlling the rate of energy production • Stored energy: high-energy phosphates • Bioenergetics: basic energy systems • Interaction among energy systems

  3. Terminology • Substrates • Fuel sources from which we make energy (adenosine triphosphate [ATP]) • Carbohydrate, fat, protein • Bioenergetics • Process of converting substrates into energy • Performed at cellular level • Metabolism: chemical reactions in the body

  4. Measuring Energy Release • Can be calculated from heat produced • 1 calorie (cal) = heat energy required to raise 1 g of water from 14.5°C to 15.5°C • 1,000 cal = 1 kcal = 1 Calorie (dietary)

  5. Substrates: Fuel for Exercise • Carbohydrate, fat, protein • Carbon, hydrogen, oxygen, nitrogen • Energy from chemical bonds in food stored in high-energy compound ATP • Resting: 50% carbohydrate, 50% fat • Exercise (short): more carbohydrate • Exercise (long): carbohydrate, fat

  6. Carbohydrate • All carbohydrate converted to glucose • 4.1 kcal/g; ~2,500 kcal stored in body • Primary ATP substrate for muscles, brain • Extra glucose stored as glycogen in liver, muscles • Glycogen converted back to glucose when needed to make more ATP • Glycogen stores limited (2,500 kcal), must rely on dietary carbohydrate to replenish

  7. Fat • Efficient substrate, efficient storage • 9.4 kcal/g • +70,000 kcal stored in body • Energy substrate for prolonged, less intense exercise • High net ATP yield but slow ATP production • Must be broken down into free fatty acids (FFAs) and glycerol • Only FFAs are used to make ATP

  8. Table 2.1

  9. Protein • Energy substrate during starvation • 4.1 kcal/g • Must be converted into glucose (gluconeogenesis) • Can also convert into FFAs (lipogenesis) • For energy storage • For cellular energy substrate

  10. Figure 2.1

  11. Controlling Rate of Energy Production by Substrate Availability • Energy released at a controlled rate based on availability of primary substrate • Mass action effect • Substrate availability affects metabolic rate • More available substrate = higher pathway activity • Excess of given substrate = cells rely on that energy substrate more than others

  12. Controlling Rate of Energy Production by Enzyme Activity • Energy released at a controlled rate based on enzyme activity in metabolic pathway • Enzymes • Do not start chemical reactions or set ATP yield • Do facilitate breakdown (catabolism) of substrates • Lower the activation energy for a chemical reaction • End with suffix -ase • ATP broken down by ATPase

  13. Figure 2.2

  14. Controlling Rate of Energy Production by Enzyme Activity • Each step in a biochemical pathway requires specific enzyme(s) • More enzyme activity = more product • Rate-limiting enzyme • Can create bottleneck at an early step • Activity influenced by negative feedback • Slows overall reaction, prevents runaway reaction

  15. Figure 2.3

  16. Stored Energy: High-Energy Phosphates • ATP stored in small amounts until needed • Breakdown of ATP to release energy • ATP + water + ATPase  ADP + Pi + energy • ADP: lower-energy compound, less useful • Synthesis of ATP from by-products • ADP + Pi + energy  ATP (via phosphorylation) • Can occur in absence or presence of O2

  17. Figure 2.4

  18. Bioenergetics: Basic Energy Systems • ATP storage limited • Body must constantly synthesize new ATP • Three ATP synthesis pathways • ATP-PCr system (anaerobic metabolism) • Glycolytic system (anaerobic metabolism) • Oxidative system (aerobic metabolism)

  19. ATP-PCr System • Anaerobic, substrate-level metabolism • ATP yield: 1 mol ATP/1 mol PCr • Duration: 3 to 15 s • Because ATP stores are very limited, this pathway is used to reassemble ATP

  20. ATP-PCr System • Phosphocreatine (PCr): ATP recycling • PCr + creatine kinase  Cr + Pi + energy • PCr energy cannot be used for cellular work • PCr energy can be used to reassemble ATP • Replenishes ATP stores during rest • Recycles ATP during exercise until used up (~3-15 s maximal exercise)

  21. Figure 2.5

  22. Figure 2.6

  23. Control of ATP-PCr System:Creatine Kinase (CK) • PCr breakdown catalyzed by CK • CK controls rate of ATP production • Negative feedback system • When ATP levels  (ADP ), CK activity  • When ATP levels , CK activity 

  24. Glycolytic System • Anaerobic • ATP yield: 2 to 3 mol ATP/1 mol substrate • Duration: 15 s to 2 min • Breakdown of glucose via glycolysis

  25. Glycolytic System • Uses glucose or glycogen as its substrate • Must convert to glucose-6-phosphate • Costs 1 ATP for glucose, 0 ATP for glycogen • Pathway starts with glucose-6-phosphate, ends with pyruvic acid • 10 to 12 enzymatic reactions total • All steps occur in cytoplasm • ATP yield: 2 ATP for glucose, 3 ATP for glycogen

  26. Glycolytic System • Cons • Low ATP yield, inefficient use of substrate • Lack of O2 converts pyruvic acid to lactic acid • Lactic acid impairs glycolysis, muscle contraction • Pros • Allows muscles to contract when O2 limited • Permits shorter-term, higher-intensity exercise than oxidative metabolism can sustain

  27. Glycolytic System • Phosphofructokinase (PFK) • Rate-limiting enzyme ATP ( ADP)   PFK activity  ATP   PFK activity • Also regulated by products of Krebs cycle • Glycolysis = ~2 min maximal exercise • Need another pathway for longer durations

  28. Oxidative System • Aerobic • ATP yield: depends on substrate • 32 to 33 ATP/1 glucose • 100+ ATP/1 FFA • Duration: steady supply for hours • Most complex of three bioenergetic systems • Occurs in the mitochondria, not cytoplasm

  29. Oxidation of Carbohydrate • Stage 1: Glycolysis • Stage 2: Krebs cycle • Stage 3: Electron transport chain

  30. Figure 2.8

  31. Oxidation of Carbohydrate:Glycolysis Revisited • Glycolysis can occur with or without O2 • ATP yield same as anaerobic glycolysis • Same general steps as anaerobic glycolysis but, in the presence of oxygen, • Pyruvic acid  acetyl-CoA, enters Krebs cycle

  32. Oxidation of Carbohydrate:Krebs Cycle • 1 Molecule glucose  2 acetyl-CoA • 1 molecule glucose  2 complete Krebs cycles • 1 molecule glucose  double ATP yield • 2 Acetyl-CoA  2 GTP  2 ATP • Also produces NADH, FADH, H+ • Too many H+ in the cell = too acidic • H+ moved to electron transport chain

  33. Figure 2.9

  34. Oxidation of Carbohydrate:Electron Transport Chain • H+, electrons carried to electron transport chain via NADH, FADH molecules • H+, electrons travel down the chain • H+ combines with O2 (neutralized, forms H2O) • Electrons + O2 help form ATP • 2.5 ATP per NADH • 1.5 ATP per FADH

  35. Oxidation of Carbohydrate:Energy Yield • 1 glucose = 32 ATP • 1 glycogen = 33 ATP • Breakdown of net totals • Glycolysis = +2 (or +3) ATP • GTP from Krebs cycle = +2 ATP • 10 NADH = +25 ATP • 2 FADH = +3 ATP

  36. Figure 2.10

  37. Figure 2.11

  38. Oxidation of Fat • Triglycerides: major fat energy source • Broken down to 1 glycerol + 3 FFAs • Lipolysis, carried out by lipases • Rate of FFA entry into muscle depends on concentration gradient • Yields ~3 to 4 times more ATP than glucose • Slower than glucose oxidation

  39. b-Oxidation of Fat • Process of converting FFAs to acetyl-CoA before entering Krebs cycle • Requires up-front expenditure of 2 ATP • Number of steps depends on number of carbons on FFA • 16-carbon FFA yields 8 acetyl-CoA • Compare: 1 glucose yields 2 acetyl-CoA • Fat oxidation requires more O2 now, yields far more ATP later

  40. Oxidation of Fat:Krebs Cycle, Electron Transport Chain • Acetyl-CoA enters Krebs cycle • From there, same path as glucose oxidation • Different FFAs have different number of carbons • Will yield different number of acetyl-CoA molecules • ATP yield will be different for different FFAs • Example: for palmitic acid (16 C): 129 ATP net yield

  41. Table 2.2

  42. Oxidation of Protein • Rarely used as a substrate • Starvation • Can be converted to glucose (gluconeogenesis) • Can be converted to acetyl-CoA • Energy yield not easy to determine • Nitrogen presence unique • Nitrogen excretion requires ATP expenditure • Generally minimal, estimates therefore ignore protein metabolism

  43. Control of Oxidative Phosphorylation:Negative Feedback • Negative feedback regulates Krebs cycle • Isocitrate dehydrogenase: rate-limiting enzyme • Similar to PFK for glycolysis • Regulates electron transport chain • Inhibited by ATP, activated by ADP

  44. Figure 2.12

  45. Interaction Among Energy Systems • All three systems interact for all activities • No one system contributes 100%, but • One system often dominates for a given task • More cooperation during transition periods

  46. Figure 2.13

  47. Table 2.3

  48. Oxidative Capacity of Muscle • Not all muscles exhibit maximal oxidative capabilities • Factors that determine oxidative capacity • Enzyme activity • Fiber type composition, endurance training • O2 availability versus O2 need

  49. Enzyme Activity • Not all muscles exhibit optimal activity of oxidative enzymes • Enzyme activity predicts oxidative potential • Representative enzymes • Succinate dehydrogenase • Citrate synthase • Endurance trained versus untrained

  50. Figure 2.14

More Related