Reduced NAD and the chain: Higher Level only: This statement is Higher Level only. It opens the last stage of aerobic respiration, continued in 3.2.14 to 3.2.16.
Practise this as you read
- Outline how reduced NAD passes energy to the chain.
- Predict the effects of blocking the chain.
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The big idea: The energy from glucose now sits in reduced NAD (and reduced FAD). Reduced NAD hands a pair of electrons to the first carrier of the electron transport chain in the inner mitochondrial membrane. As the electrons pass from carrier to carrier, their energy is released in small steps.
The points to remember
- The chain is a series of carrier proteins in the inner membrane (cristae).
- Reduced NAD gives 2 electrons to the first carrier and becomes NAD again.
- Electrons pass from carrier to carrier, releasing energy in steps.
- Reduced FAD gives its electrons further along, so it yields less ATP than reduced NAD.
- If the chain is blocked, reduced NAD builds up and ATP production falls.
Remember it as: Reduced NAD is a delivery van: it drops off electrons at the first carrier and goes back for more.
Real example: rotenone. Rotenone, a plant toxin once used to kill fish and insect pests, blocks the first carrier. Electrons from reduced NAD cannot enter the chain, so aerobic respiration slows dramatically.
Trap: Reduced NAD does not make ATP itself; it delivers electrons whose energy the chain uses.
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How it is asked: Expect an Outline of what happens when the chain is blocked by a toxin, or of how reduced NAD passes energy to the chain.
IB-style questionOutline[4 marks]
A toxin blocks the electron transport chain. Outline the consequences for cell respiration.
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