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Fueling Exercise & Energy Systems (Stored Energy: High-Energy…

- - - - All carbohydrate converted to glucose
      - Glycogen converted back to glucose when needed to make more ATP
      - Glycogen stores limited (2,500 cal), must rely on dietary carbohydrate to replenish
      - Oxidation of Carbohydrate
        
        Stage 1: Glycolysis
        
        Glycolysis can occur with or without O2
        
        Stage 2: Krebs cycle
        
        Stage 3: Electron transport chain
        
        H+, electrons carried to electron transport chain via NADH, FADH molecules
        
        H+, electrons travel down the chain
        
        Energy Yield
        
        1 glucose = 32 ATP
        
        1 glycogen = 33 ATP
        
        Breakdown of net totals
    - - Efficient substrate, efficient storage
      - Energy substrate for prolonged, less intense exercise
      - Oxidation of Fat
        
        Triglycerides: major fat energy source
        
        Rate of FFA entry into muscle depends on concentration gradient
        
        Yields ~3 to 4 times more ATP than glucose
        
        Slower than glucose oxidation
      - beta-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
      - 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
    - - Energy substrate during starvation
      - Can also convert into FFAs (lipogenesis)
      - Oxidation of Protein
        
        Rarely used as a substrate
        
        Energy yield not easy to determine
- - - - ATP-PCr system (anaerobic metabolism)
        
        Anaerobic, substrate-level metabolism
        
        ATP yield: 1 mol ATP/1 mol PCr
        
        Duration: upto 15 s
        
        Because ATP stores are very limited, this pathway is used to reassemble ATP
        
        Phosphocreatine (PCr): ATP recycling
        
        Replenishes ATP stores during rest
        
        Recycles ATP during exercise until used up (~3-15 s maximal exercise)
        
        PCr breakdown catalyzed by CK
        CK controls rate of ATP production
      - Glycolytic system (anaerobic metabolism)
        
        ATP yield: 2 to 3 mol ATP mol substrate
        
        Duration: upto 2 mins
        
        Breakdown of glucose via glycolysis
        
        Uses glucose or glycogen as its substrate
        
        Pathway starts with glucose-6-phosphate, ends with pyruvic acid
        
        Phosphofructokinase (PFK)
        
        Glycolysis = ~2 min maximal exercise
        
        Need another pathway for longer durations
      - Oxidative system (aerobic metabolism)
        
        ATP yield: depends on substrate
        
        Duration: steady supply for hours
        
        Most complex of three bioenergetic systems
        
        Occurs in the mitochondria, not cytoplasm