Electron transport chain

Biology Unit 5

Electron transport chain

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Biology Unit 5
Revision Notes
Topic 7: Run for your life
10. Describe the synthesis of ATP by oxidative
phosphorylation, associated with the electron
transport chain in mitochondria, including the role of
chemiosmosis and ATPase.
Aerobic respiration takes place in two stages:
First the Krebs Cycle, as seen previously
In the second stage, most of the ATP generated in aerobic respiration is synthesised by
oxidative phosphorylation associated with the electron transport chain. This involves
chemiosmosis and the enzyme ATPase. It takes place on the Cristae of the mitochondria
Electron Transport Chain
This is how molecules of ATP are produced. The process is called Oxidative Phosphorylation:
ADP + Pi ATP (in the presence of O)
1. Hydrogen released from the Krebs Cycle is accepted by NAD to form NADH (reduction)
2. NADH `gives' its hydrogen to FAD (FAD is now reduced to FADH) and produces 1 x ATP
3. FADH `gives' its hydrogen (and electrons) to cytochrome (a protein pigment containing Fe
ions, similar to haemoglobin) and this produces 1 x ATP
4. The cytochrome then reduces (gives hydrogen and electrons to) the enzyme Cytochrome
Oxidase, producing 1 x ATP
5. Oxygen (originally from the lungs) accepts the final hydrogen to form water (reduction)
Therefore, each NADH results in 3 x ATP molecules.
Text Book: p.138 - 140

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Biology Unit 5
Revision Notes
Chemiosmotic Theory
In 1961, Peter Mitchell put forward a theory to explain the production of ATP. Previously, it was
thought that a high-energy phosphate group was directly transferred to ADP from another
intermediate. No intermediate was ever found and evidence built up to support Mitchell's theory
The Theory
Hydrogen ions from the ETC (after step 4) move across the inner membrane of the mitochondria
against the concentration gradient (Active Transport). The energy needed for this is supplied by the
ETC.…read more


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