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PowerPoint ® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College C H A P T E R © 2013 Pearson Education, Inc.© Annie Leibovitz/Contact.

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Presentation on theme: "PowerPoint ® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College C H A P T E R © 2013 Pearson Education, Inc.© Annie Leibovitz/Contact."— Presentation transcript:

1 PowerPoint ® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College C H A P T E R © 2013 Pearson Education, Inc.© Annie Leibovitz/Contact Press Images 9 Muscles and Muscle Metabolism

2 5/5/2015 MDufilho2 Introduction: Muscle Metabolism – Energy for Contraction Energy is never created nor destroyed, only stored or released Bonds = energy – ATP is the currency for cellular energy Energy is stored in the bonds.

3 MDufilho Muscle Metabolism: Energy for Contraction ATP only source used directly for contractile activities –Move and detach cross bridges, calcium pumps in SR, return of Na + & K + after excitation-contraction coupling Available stores of ATP depleted in 4–6 seconds 5/5/20153

4 MDufilho Muscle Metabolism: Energy for Contraction ATP regenerated by: –Direct phosphorylation of ADP by creatine phosphate (CP) –Anaerobic pathway (glycolysis  lactic acid) –Aerobic respiration 5/5/20154

5 MDufilho Figure 9.19a Pathways for regenerating ATP during muscle activity. Direct phosphorylation Coupled reaction of creatine Phosphate (CP) and ADP Energy source: CP Oxygen use: None Products: 1 ATP per CP, creatine Duration of energy provided: 15 seconds Creatine kinase Creatine 5/5/20155

6 MDufilho Figure 9.19b Pathways for regenerating ATP during muscle activity. Anaerobic pathway Glycolysis and lactic acid formation Energy source: glucose Glucose (from glycogen breakdown or delivered from blood) Glycolysis in cytosol Pyruvic acid net gain Released to blood Lactic acid Oxygen use: None Products: 2 ATP per glucose, lactic acid Duration of energy provided: seconds, or slightly more 2 5/5/20156

7 MDufilho Anaerobic Pathway At 70% of maximum contractile activity –Bulging muscles compress blood vessels; oxygen delivery impaired –Pyruvic acid converted to lactic acid Lactic acid –Diffuses into bloodstream –Used as fuel by liver, kidneys, and heart –Converted back into pyruvic acid or glucose by liver 5/5/20157

8 MDufilho8 Anaerobic Glycolysis Fast pathway, but does not produce much ATP Important for the first 30 – 40 sec. of strenuous activity if enzymes and fuel are available Stored ATP, CP and glycolysis can support strenuous muscle activity for 60 sec. At full speed lactic acid accumulates, lowering pH which halts reaction At full speed, glucose might not be supplied fast enough

9 MDufilho Aerobic Pathway Produces 95% of ATP during rest and light to moderate exercise; slow Series of chemical reactions that require oxygen; occur in mitochondria –Breaks glucose into CO 2, H 2 O, and large amount ATP Fuels - stored glycogen, then bloodborne glucose, pyruvic acid from glycolysis, and free fatty acids 5/5/20159

10 MDufilho Figure 9.19c Pathways for regenerating ATP during muscle activity. Aerobic pathway Aerobic cellular respiration Energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism Glucose (from glycogen breakdown or delivered from blood) Pyruvic acid Fatty acids Amino acids net gain per glucose Oxygen use: Required Products: 32 ATP per glucose, CO 2, H 2 O Duration of energy provided: Hours Aerobic respiration in mitochondria Aerobic respiration in mitochondria 32 5/5/201510

11 5/5/2015 MDufilho11 Aerobic Respiration – Krebs Cycle Occurs in the mitochondrial matrix and is fueled by pyruvic acid (from glucose) and fatty acids Prep. Step - Pyruvic acid is converted to acetyl CoA Requires oxygen, but does not directly use it Preferred method of ATP production During rest/light exercise AR yields 95% of ATP needed

12 Krebs Cycle Coenzyme A shuttles acetic acid to an enzyme of the Krebs cycle Each acetic acid is decarboxylated and oxidized, generating: –3 NADH + H + –1 FADH 2 –2 CO 2 –1 ATP 5/5/ MDufilho

13 Figure 24.7 Simplified version of the Krebs (citric acid) cycle. Glycolysis Krebs cycle Electron trans- port chain and oxidative phosphorylation Carbon atom Inorganic phosphate Coenzyme A Cytosol Mitochondrion (matrix) Transitional phase Oxaloacetic acid (pickup molecule) Malic acid Fumaric acid Succinic acid Pyruvic acid from glycolysis Krebs cycle Citric acid (initial reactant) Isocitric acid α-Ketoglutaric acid Succinyl-CoA 5/5/201513

14 MDufilho Summary of ATP Production Complete oxidation of 1 glucose molecule Glycolysis + Krebs cycle + electron transport chain  CO 2 + H 2 O  32 molecules ATP –By both substrate-level and oxidative phosphorylation But, energy required to move NADH + H + generated in glycolysis into mitochondria  final total ~ 30 molecules ATP –Still uncertainty on final total 5/5/201514

15 MDufilho Figure Energy yield during cellular respiration. Cytosol Electron shuttle across mitochondrial membrane Glycolysis Glucose Pyruvic acid (4 ATP – 2 ATP used for activation energy) by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation Typical ATP yield per glucose Krebs cycle 2 Acetyl CoA Electron transport chain and oxidative phosphorylation Mitochondrion 5/5/201515

16 MDufilho Energy Systems Used During Sports Aerobic endurance –Length of time muscle contracts using aerobic pathways Anaerobic threshold –Point at which muscle metabolism converts to anaerobic 5/5/201516

17 MDufilho Figure 9.20 Comparison of energy sources used during short-duration exercise and prolonged-duration exercise. Short-duration exercise 6 seconds ATP stored in muscles is used first. 10 seconds ATP is formed from creatine phosphate and ADP (direct phosphorylation). 30–40 seconds Glycogen stored in muscles is broken down to glucose, which is oxidized to generate ATP (anaerobic pathway). End of exercise Prolonged-duration exercise Hours ATP is generated by breakdown of several nutrient energy fuels by aerobic pathway. 5/5/201517

18 MDufilho Muscle Fatigue Physiological inability to contract despite continued stimulation Occurs when –Ionic imbalances (K +, Ca 2+, P i ) interfere with E ‑ C coupling –Prolonged exercise damages SR and interferes with Ca 2+ regulation and release Total lack of ATP occurs rarely, during states of continuous contraction, and causes contractures (continuous contractions) 5/5/201518

19 MDufilho Excess Postexercise Oxygen Consumption To return muscle to resting state –Oxygen reserves replenished –Lactic acid converted to pyruvic acid –Glycogen stores replaced –ATP and creatine phosphate reserves replenished All require extra oxygen; occur post exercise 5/5/201519

20 MDufilho Heat Production During Muscle Activity ~40% of energy released in muscle activity useful as work Remaining energy (60%) given off as heat Dangerous heat levels prevented by radiation of heat from skin and sweating Shivering - result of muscle contractions to generate heat when cold 5/5/201520

21 5/5/2015 MDufilho21 Skeletal Muscle Cramps Cause Insufficient blood flow or oxygen = anaerobic ATP production Lactic acid accumulates and causes muscle irritation Due to dehydration and insufficient K +, Ca 2+ and rarely Na + Prevention Hydration, fitness and adequate diet

22 MDufilho Muscular Dystrophy Duchenne muscular dystrophy (DMD): –Most common and severe type –Inherited, sex-linked, carried by females and expressed in males (1/3500) as lack of dystrophin Cytoplasmic protein that stabilizes sarcolemma Fragile sarcolemma tears  Ca 2+ entry  damaged contractile fibers  inflammatory cells  muscle mass drops –Victims become clumsy and fall frequently; usually die of respiratory failure in 20s 5/5/201522

23 MDufilho Muscular Dystrophy –No cure –Prednisone improves muscle strength and function –Myoblast transfer therapy disappointing –Coaxing dystrophic muscles to produce more utrophin (protein similar to dystrophin) successful in mice –Viral gene therapy and infusion of stem cells with correct dystrophin genes show promise 5/5/201523


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