Summary of Eduqas Component 1, Unit 1: ATP Synthesis (also applicable to WJEC). Easy to digest but comprehensive information, including diagrams and highlighted key words. Written by a Year 13 student, predicted A-A*.
Based on official Eduqas teacher guidance:
(a) the synthesis of ATP involving...
ATP can be reformed from ADP + Pi in a condensation reaction. This occurs in 3 ways:
• Photophosphorylation – occurs in the chloroplast during photosynthesis. Energy originates from light.
• Oxidative phosphorylation – occurs in the mitochondria during respiration. Energy comes from high energy bonds in organic
molecules.
• Substrate level phosphorylation – occurs in the mitochondria during aerobic and anaerobic respiration.
Photophosphorylation and oxidative phosphorylation take place in the thylakoid membrane of the chloroplast, and the inner
membrane of the mitochondria.
These membranes contain the electron transport chain – a series of alternating proton pumps and electron carriers.
The passing of electrons along the chain results in chemiosmosis – the movement of ions across a selectively permeable
membrane down their electrochemical gradient. This results in the formation of ATP.
1. Hydrogen atoms split into H+ (protons) and e- (electrons).
2. Electrons are passed through the electron transport chain in a series of REDOX reactions (Oxidation Is Loss, Reduction Is Gain
– of electrons).
They lose energy as they pass from carrier to carrier.
3. The energy from the electrons is used to ‘pump’ the protons across the membrane.
This creates a higher concentration of protons on one side of the membrane – an electrochemical gradient, which has
potential energy.
4. The protons diffuse down the electrochemical/proton gradient through ATP synthetase enzyme located in the stalked
particles in the membrane (chemiosmosis).
5. The energy is used by the enzyme to synthesise ATP from ATP and Pi.
Evidence for chemiosmosis:
• pH of intermembrane space is lower than pH of matrix.
Shows there is a proton gradient between the intermembrane space and matrix, as low pH = high concentration of protons.
• Mitochondria in pH8 solution produced no ATP.
Shows that proton gradient is used by mitochondria to make ATP; acidic conditions are not maintained in the intermembrane
space in pH8 solution, so the proton gradient is lost.
• No ATP produced with uncouplers.
Shows that a proton gradient is used by mitochondria to make ATP.
Uncoupling proteins can be found on the inner mitochondrial membrane and act as proton channels. They allow electron
transport, but it is ‘uncoupled’ from ATP synthesis as no proton gradient is generated. The energy from electron transfer is
lost as heat instead, leading to over-heating and sometimes death.
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