AQA Biology A2 Unit 4 Respiration

Aerobic
1. Oxygen present
2. 4 stages: Glycolysis, Link Reaction, Krebs Cycle & Electron Transport Chain
  1. 1: GLYCOLYSIS
    1. Occurs in the cytoplasm
    2. Break down of Glucose 6C into 2 x Pyruvate 3C
      1. 1. Phosphorylation of Glucose
        Glucose + 2 Pi from hydrolysis of ATP gives energy (Lower AE for next reactions)
      2. 2. Splitting of phosphorylated Glucose.
        1 x Glucose (6C) ---> 2 x Triose Phosphate molecules (3C)
      3. 3. Oxidation (H loss) of Triose Phosphate
        NAD + H ---> Reduced NAD
      4. 4. 2 x ATP Produced ( Direct Substrate Level Phosphorylation).
        Enzymes control reaction to 2 x Triose Phosphate ---> 2 x Pyruvate (3C)
        Pi + ADP ---> 4 x ATP However, 2 x ATP hydrolysed at start, so NET ATP = 2. (+ 2 x Pyruvate & 2 x Reduced NAD)
    3. Does not require oxygen
  2. 2: LINK REACTION
    1. Occur in the mitochondria.
    2. Oxidation (H loss) of Pyruvate from Glycolysis.
      1. 2 x Pyruvate actively transported from cytoplasm to mitochondria.
  3. 4: ELECTRON TRANSPORT CHAIN
    1. Occurs on the cristae using enzymes on the membrane to synthesise ATP.
    2. The H on the reduced coenzymes loss the eletrons; it is these that are transported along the ETC.
      1. 1: Coenzymes Reduced NAD & FAD are OXIDISED (loss) and releases electrons and H to create a proton gradient.
      2. 2: Electron is passed along protein carriers, losing energy as it goes.
      3. 3: Series of Oxidation and Reduction reactions. OXYGEN is the FINAL RECEPTOR and combines with H ---> WATER.
      4. 4: Electron energy is now stored in the proton gradient. This energy synthesises ATP (INDIRECT OXIDATIVE PHOSPHORYLATION) + ATP synthase on the stalked particles..
  4. 3: KREBS CYCLE
    1. Occurs in the matrix of the mitochondria.
    2. Break down of Acetylcoenzyme (2C + 4C molecule) into smaller (4C) molecule.
    3. Produces 1 x ATP + Reduced FAD & NAD + 2 x Carbon Dioxide.
Anaerobic
1. In Animals. NO Carbon Dioxide is released. However, In plants, Carbon Dioxide is released!
2. If no Oxygen is available, the H from reduced NAD (glycolysis) + pyruvate ---> lactate.
3. Oxidised NAD recombines with H in glycolysis.

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AQA Biology A2 Unit 4 Respiration

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