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12.2.712 · Energy and Respiration

Aerobic Respiration- Oxidative Phosphorylation — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 9 parts Lesson 13 of 18 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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12.2.7 Aerobic Respiration: Oxidative Phosphorylation — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how the electron transport chain and chemiosmosis make ATP and why oxygen is essential.Where — the inner mitochondrial membrane.Energy source — electrons ca…

  • Importance
  • Hydrogen donation
  • Proton pumping
  • Impermeable membrane
  • End of the chain
  • Return of protons

Part 1 of 7Location and overview

Location and overview
Where
  • Where the inner mitochondrial membrane.
Energy source
  • Energy source electrons carried by reduced NAD and reduced FAD.
Parts
  • Parts the electron transport chain and chemiosmosis.
Importance
  • Importance it makes most of the ATP of aerobic respiration.

Part 2 of 7The electron transport chain

Hydrogen donation
  • Hydrogen donation reduced NAD and FAD donate hydrogen, which splits into protons (H+) and electrons, regenerating NAD and FAD.
Carriers
  • Carriers electrons pass along protein complexes and mobile carriers in a series of redox reactions.
  • Carriers sit close together so electrons pass from carrier to carrier.
  • At each step electrons move to a carrier with a lower energy level.
Proton pumping
  • Proton pumping the energy released at three complexes pumps H+ from the matrix across the inner membrane into the intermembrane space.
Impermeable membrane
  • Impermeable membrane the inner membrane is impermeable to H+, so carriers must pump protons to set up the gradient.
End of the chain
  • End of the chain oxygen accepts electrons and combines with protons from the matrix to form water: 4H+ + 4e- + O2 → 2H2O.

Part 3 of 7Chemiosmosis

Gradient
  • Gradient pumping makes a high H+ concentration in the intermembrane space and a low one in the matrix, an electrochemical (proton) gradient.
Return of protons
  • H+ can return only through channels in ATP synthase, by facilitated diffusion.
ATP synthesis
  • ATP synthesis flow down the gradient rotates ATP synthase, which catalyses ADP + Pi → ATP.
Theory
  • Theory chemiosmosis was proposed by Peter Mitchell.
Energy form
  • Energy form energy is stored first in the gradient and then in ATP.
    • (proton-motive force)

Part 4 of 7Why oxygen is essential

Final acceptor
  • Final acceptor it keeps the chain running because electrons need somewhere to go.
Without oxygen
  • Without oxygen carriers become fully reduced, protons are not pumped and the gradient collapses.
Knock-on effect
  • Knock-on effect reduced NAD and FAD cannot be re-oxidised, so the Krebs cycle and link reaction also stop.
Cyanide
  • Cyanide it inhibits cytochrome oxidase, the final enzyme, and stops ATP production.
Uncouplers
  • DNP makes the membrane permeable to protons, so energy is lost as heat rather than ATP.
Thermogenin
  • Thermogenin this uncoupling protein in brown adipose tissue of newborns and hibernators lets protons leak to generate heat.

Part 5 of 7Yield

Reduced NAD
  • Reduced NAD about 2.5 ATP each.
Reduced FAD
  • Reduced FAD about 1.5 ATP each, because it donates electrons later in the chain so fewer protons are pumped.
Per glucose
  • 10 reduced NAD and 2 reduced FAD give about 28 ATP from oxidative phosphorylation.
Total
  • Total adding 4 from substrate-level phosphorylation gives about 32, reduced to about 30 after transport costs.
Older values
  • Older values some textbooks give 34 or 38.

Part 6 of 7Evidence and structure

Evidence and structure
Mitchell's theory (Nobel prize, 1978)
  • Mitchell's theory (Nobel prize, 1978) it was supported by experiments.
  • Isolated mitochondria given a substrate lowered the pH of the medium as protons were pumped out.
  • An uncoupler such as DNP removed the gradient, and ATP synthesis stopped though oxygen was still used.
  • Vesicles with ATP synthase and a light-driven bacterial proton pump made ATP in light, showing that a proton gradient alone can drive synthesis.
Chloroplasts
  • Chloroplasts similar mechanisms operate in them.
ATP synthase structure
  • Fo is embedded in the membrane and passes protons, and F1 projects into the matrix.
  • Proton flow rotates the central part.
  • Shape changes in the catalytic subunits bind ADP and phosphate and release ATP.
Cristae
  • Cristae they maximise the number of ATP synthase units and electron carriers.

Part 7 of 7More from the specification

1
ATP synthase mechanical rotary function
  • ATP synthase mechanical rotary function proton motive force across the inner mitochondrial membrane drives ATP synthase rotation, executing vital phosphorylation function.
2
Oxidative phosphorylation mechanism
  • Reduced NAD and FAD pass electrons through inner mitochondrial membrane complexes, using the released free energy to pump protons into the intermembrane space.
3
Chemiosmosis and ATP synthase
  • Protons flow down their electrochemical gradient through the hydrophilic channel of ATP synthase back into the matrix, coupling proton-motive force to ADP phosphorylation.
4
Oxygen as the terminal electron acceptor
  • Molecular oxygen acts as the final electron and proton acceptor at complex IV, combining to form metabolic water and preventing electron transport stall.
5
Cytoplasmic glycolysis stages
  • Cytoplasmic glycolysis stages glycolysis breaks down each glucose molecule into two pyruvate molecules within cell cytoplasm, yielding net ATP.
6
Anaerobic respiration in yeast versus muscle
  • Anaerobic respiration in yeast versus muscle anaerobic pathways reduce pyruvate to ethanol in yeast cells or lactate in mammalian muscle cells.
7
Mitochondrial respiratory stages
  • Mitochondrial respiratory stages pyruvate enters mitochondria where link reaction, Krebs cycle,
  • and oxidative phosphorylation complete aerobic breakdown at optimal metabolic temperatures.
8
Anaerobic
  • Without oxygen.
9
Glycolysis
  • Splitting of glucose to pyruvate in the cytoplasm.
10
Pyruvate
  • A 3-carbon product of glycolysis.
11
Ethanol
  • Alcohol produced by yeast in anaerobic respiration.
12
Lactate
  • The product of anaerobic respiration in human cells.
13
Fermentation
  • Anaerobic respiration by yeast producing ethanol and carbon dioxide.
14
Anaerobic respiration
  • Respiration without oxygen, releasing much less energy per glucose molecule.
15
Ethanol fermentation
  • Decarboxylation of pyruvate to ethanal, then reduction to ethanol.

Key terms

TermMeaning
Electron transport chainA series of carriers in the inner membrane passing electrons and pumping protons.
ChemiosmosisATP synthesis driven by proton flow through ATP synthase.
Proton gradientA difference in H^{+} concentration across the inner membrane.
Final electron acceptorOxygen, which combines with electrons and protons to form water.
UncouplerA substance that makes the membrane leak protons, losing energy as heat.
Cytochrome oxidaseThe final enzyme of the chain, inhibited by cyanide.

Avoid these mistakes

1
Saying oxygen is used to make ATP directly — it is the final electron acceptor forming water.
2
Saying protons cross the membrane freely — the membrane is impermeable and they pass through ATP synthase.
3
Saying electrons are pumped across the membrane — the energy from electrons pumps protons.
4
Saying reduced FAD gives the same ATP as reduced NAD — it gives fewer.

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