The stages of aerobic respiration and what happens in each stage

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Stage 1: Glycolysis

  • Happens in the cytoplasm
  • Breakdown of Glycogen

1. Glycogen converted to glucose (6 carbons)

2. 2 ATP break down glucose to intermediate 3C compounds

3. Intermediate 3C compound is oxidised

4. 2 hydrogen atoms removed and taken up by coenzyme NAD

5. Pyruvate produced

6. Substrate level phosphorylation occurs- phosphate from intermediate compounds is transferred to ADP creating ATP

  • Net gain of 2 ATP
  • 2 Pairs of hydrogen atoms produced
  • 2 pyruvate molecules produced
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Stage 2: Link reaction

  • Pyruvate from glycolysis passes into mitochondria

1. Pyruvate is decarboxylated (Carbon dioxide is released as a waste product)

2. It is then dehydrogenated (2 hydrogens are removed and taken up by coenzyme NAD)

3. resulting 2 carbon molecule combines with coenzyme A to form Acetyl CoA (2C)

  • Products: 2 Acetyl CoA, 2 CO2, 2 Pairs Hydrogen atoms
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Stage 3: Krebs cycle

1. Acetyl CoA combines with a 4C compound to create a 6C compound.

2. Decarboxylation (release of CO2) and dehydrogenation (release of H2, taken up by NAD) occur

3. 5C compound is left

4. Decarboxylation reoccurs

5. Substrate level phosphorylation occurs (releasing 1 ATP)

6. Dehydrogenation happens 3 more times (twice taken up by NAD, once by FAD)

7. 4C compound remains, to start cycle again, combining with a new Acetyl CoA molecule

8. This happens twice as there were 2 pyruvate molecules(therefore 2 Acetyl CoA) from one glucose

  • Products for 2 Acetyl CoA: 4 CO2, 2ATP, 16 pairs H atoms
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Stage 4: Electron transport chain

  • Inner mitochondrial membrane

1. Reduced coenzyme (Red.NAD and Red. FAD) carries H+ and electron to electron transport chain

2. Electrons pass from one electron carrier to the next in a series of redox reactions (Carrier is reduced when recieves the electrons and oxidised when it passes them on)

3. Protons (H+) move across inner mitochondrial membrane creating high H+ Concentrations.

4.H+ diffuse back into mitochndrial matrix down electrochamical gradient

5.H+ diffusion allows ATPase to catalyse ATP synthesis

6. Electrons and H+ ions combine to form hydrogen atoms which combine with oxygen to create water

  • This method of producing ATP is called Oxidative Phosphorylation
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How much ATP is produced?

  • Each Reduced NAD produces 3ATP when reoxidised
  • Each Reduced FAD produces 2ATP when reoxidised


Glycolysis- 2ATP, 2NAD

Link reaction- 2NAD (one for each Pyruvate molecule)

Krebs Cycle- 2ATP (one for each Acetyl CoA), 6NAD (3 for each Acetyl CoA), 2FAD (one for each Acetyl CoA)

Electron transport chain- 10 reduced NAD (3x10=30ATP), 2 reduced FAD (2x2=4ATP)

2ATP(glyc.)+2ATP(Krebs)+34ATP(ETC)= 38ATP

  • Total of 38ATP produced per glucose molecule
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