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Chapter 7C: Electron Transport Chain, Regulation of metabolism,…

- - - - ends up at strong electron acceptor (oxygen)
- - - - result: high H+ in intermembrane space, low in matrix
      - The gradient of protons provides a source of potential energy that's converted into chemical energy stored in ATP
        
        protons in the intermembrane space diffuse DOWN their gradients through a channel into the matrix
        
        movement of protons through the channel is coupled by ATP synthesis (ATP synthase forms the channel in the inner membrane through which protons flow, proton flow through the channel makes it possible for the ATP synthase to synthesize ATP)
- - - - Variety of possible outputs
        
        intermediates in the citric acid cycle can be used in anabolism to build many other molecules
      - Variety of possible inputs
        
        ex. amino acids --> acetyl-CoA
        
        fatty acids can be broken down into Acetyl-CoA, used for the citric acid cycle
    - - can be stored for later
        
        starch (plants)
        
        glycogen (animals)
      - What decides where glucose-6Phosphate goes?
        
        the activity of enzyme PFK-1 controls the fate of Glc-6P
        
        PFK1 catalyzes putting the second phosphate on the 6-carbon sugar (then glycolysis happens)
        
        PFK-1 is highly regulated by allostery
        
        Activation vs. Inhibition of PFK-1
        
        Low ATP levels: activation of PFK-1 (ADP and AMP are allosteric activators), allows glycolysis to continue
        
        High ATP/citrate levels: inhibits PFK-1 (ATP and citrate are allosteric inhibitors), glycolysis slows
- - - - oxidized electron carriers (NAD+) would disappear - nowhere to put electrons
  - - - Fermentation disadvantages
        
        wasteful
        
        put electrons back into pyruvate (reduce pyruvate to oxidize NADH)
        
        only produces a modest amount of ATP (2ATP/ glucose)
        
        could've used potential of pyruvate to do more
        
        products are toxic
        
        pyruvate generates derivative that accepts electrons from NADH with an enzyme and generates ethanol (toxic)
      - Pyruvate can accept electrons directly with enzyme from NADH to generate NAD+
      - Why ferment at all?
        
        Organism can survive when there's no oxygen (they've found out how to generate ATP without oxygen)
        
        Fermentation is fast
        
        Aerobic organisms use it too
        
        ex. budding yeast
        
        preferentially runs fermentation even though oxygen is present
        
        grow on tree exudates and rotting fruit
        
        very high in glucose and directly usable sugar, but they're not always there
        
        1 more item...
        
        Muscle contraction
        
        under duress (when you run fast), oxygen levels drop
        
        muscles can generate ATP faster using fermentation than using respiration
        
        1 more item...
        
        Many cancer cells do this too
        
        tumor cells frequently run glycolysis full tilt, allowing them to grow faster and suppress growth of cells around it
        
        Fermentation preserves food
        
        fermentation end products are growth inhibitory (prevents growth of bacteria)