AQA Unit 4 Respiration

Glycolysis, Link Reaction, Kreb's Cycle, Electron Transport Chain

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  • Occurs in the cytoplasm
  • Glucose is activated by the addition of phosphate (from the hydrolysis of ATP to ADP)
  • Phosphorylated glucose is split into two molecules of 3-carbon TP (triose phosphate)
  • Hydrogen is removed from each TP and transferred to NAD
  • NAD is reduced by the addition of hydrogen
  • Enzyme controlled reactions convert each TP to pyruvate
  • Two molecules of TP are regenerated from ADP
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Link reaction

  • The pyruvate molecules in the cytoplasm are actively transported into the mitochondrial matrix
  • Here, pyruvate is oxidised by removing hydrogen
  • This hydrogen is accepted by and reduces NAD
  • The 2-carbon molecule that is produced, acetyl group, combines with coenzyme A
  • AcetylcoenzymeA is formed
  • A molecule of CO2 is formed
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Kreb's Cycle

  • The 2-carbon molecule acetylcoenzyme A from the link reaction combines with a 4-carbon molecule
  • A 6-carbon molecule is produced
  • 6-carbon molecule is oxidised by the loss of hydrogen and a molecule of carbon dioxide
  • A 4-carbon molecule and a single molecule of ATP is formed in substrate-level phosphorylation
  • The 4-carbon molecule that is formed can recombine with another molecule of acetylcoenzyme A
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Electron transport chain

  • The hydrogen atoms produced in glycolysis and the Kreb's Cycle combine with NAD and FAD
  • The reduced NAD and FAD donate electrons to the first molecule in the electron transport chain
  • This releases protons from the hydrogen atoms, the protons are then actively transported across the inner mitochondrial membrane
  • The electrons pass down the electron transport chain in a series of redox reactions
  • The electrons lose energy as they pass down the chain
  • Some of this energy is used to combine ADP and Pi to form ATP, and the remaining energy is used as heat
  • The protons accumulate in the space between the two mitochondrial membranes before they diffuse back into the mitochondrial matrix through protein channels
  • The electrons combine with protons and oxygen to form water
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