AQA Biology A2 Unit 4 Respiration

AQA Biology A2 Unit 4 Respiration

1. Aerobic

   • Oxygen present
   • 4 stages: Glycolysis, Link Reaction, Krebs Cycle & Electron Transport Chain
     • 1: GLYCOLYSIS
       • Occurs in the cytoplasm
       • Break down of Glucose 6C into 2 x Pyruvate 3C
         • 1. Phosphorylation of Glucose
           • Glucose + 2 Pi from hydrolysis of ATP gives energy (Lower AE for next reactions)
         • 2. Splitting of phosphorylated Glucose.
           • 1 x Glucose (6C) ---> 2 x Triose Phosphate molecules (3C)
         • 3. Oxidation (H loss) of Triose Phosphate
           • NAD + H ---> Reduced NAD
         • 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)
       • Does not require oxygen
     • 2: LINK REACTION
       • Occur in the mitochondria.
       • Oxidation (H loss) of Pyruvate from Glycolysis.
         • 2 x Pyruvate actively transported from cytoplasm to mitochondria.
     • 4: ELECTRON TRANSPORT CHAIN
       • Occurs on the cristae using enzymes on the membrane to synthesise ATP.
       • The H on the reduced coenzymes loss the eletrons; it is these that are transported along the ETC.
         • 1: Coenzymes Reduced NAD & FAD are OXIDISED (loss) and releases electrons and H to create a proton gradient.
         • 2: Electron is passed along protein carriers, losing energy as it goes.
         • 3: Series of Oxidation and Reduction reactions. OXYGEN is the FINAL RECEPTOR and combines with H ---> WATER.
         • 4: Electron energy is now stored in the proton gradient. This energy synthesises ATP (INDIRECT OXIDATIVE PHOSPHORYLATION) + ATP synthase on the stalked particles..
     • 3: KREBS CYCLE
       • Occurs in the matrix of the mitochondria.
       • Break down of Acetylcoenzyme (2C + 4C molecule) into smaller (4C) molecule.
       • Produces 1 x ATP + Reduced FAD & NAD + 2 x Carbon Dioxide.

2. Anaerobic

   • In Animals. NO Carbon Dioxide is released. However, In plants, Carbon Dioxide is released!
   • If no Oxygen is available, the H from reduced NAD (glycolysis) + pyruvate ---> lactate.
   • Oxidised NAD recombines with H in glycolysis.

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