Krebs cycle and oxidative phosphorylation
Introduced| English | Meaning |
|---|---|
| oxaloacetate/ˈɒksələʊsɪteɪt/ | A four-carbon compound that combines with an acetyl group to form citrate at the start of the citric acid cycle. |
| citrate/ˈsɪtreɪt/ | The six-carbon compound formed when an acetyl group combines with oxaloacetate in the citric acid cycle. |
| decarboxylation/dɪˌkɑːbəksɪˈleɪʃn/ | Removal of a carboxyl group from a molecule, releasing carbon dioxide. |
| dehydrogenation/ˌdiːhaɪˈdrɒdʒəneɪʃn/ | Removal of hydrogen from a substance, usually as part of an oxidation reaction. |
| electron transport chain/ɪˈlektrɒn ˈtrænspɔːt tʃeɪn/ | A series of electron carriers that transfer electrons through redox reactions and can establish a proton gradient for ATP production. |
| ATP synthase/ˌeɪ tiː ˈpiː ˈsɪnθeɪs/ | An enzyme complex that uses the movement of protons down their electrochemical gradient to synthesise ATP. |
| final electron acceptor/ˈfaɪnl ɪˈlektrɒn əkˈseptə/ | final electron acceptor |
| cristae/ˈkrɪstiː/ | Folds of a mitochondrion's inner membrane that increase the surface available for respiratory electron transport and ATP production. |
Squeezing out the last energy
- Acetyl CoA now enters the Krebs cycle in the matrix.
- Then the carried hydrogen powers oxidative phosphorylation — making most of the ATP.
- It all happens inside the mitochondrion.
The Krebs cycle
- The 2C acetyl group joins a 4C oxaloacetate 草酰乙酸 to make a 6C citrate 柠檬酸.
- Citrate is changed back to oxaloacetate in small steps, ready for the next acetyl group. Along the way:
- decarboxylation 脱羧 removes carbon as CO₂,
- dehydrogenation 脱氢 removes hydrogen, reducing NAD and FAD.
- The reduced NAD and FAD carry the hydrogen to the inner membrane.
The Krebs cycle releases carbon dioxide and reduced coenzymes
The Krebs cycle
Step around the cycle. Each turn strips off CO₂ and hydrogen, loading up the reduced coenzymes that make most of the ATP later.
During the Krebs cycle, what is removed?
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Each turn removes CO₂ (decarboxylation) and hydrogen (dehydrogenation), reducing the coenzymes NAD and FAD.
Each turn of the Krebs cycle removes carbon dioxide and hydrogen, reducing NAD and FAD.
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The reduced NAD and FAD then carry the hydrogen to oxidative phosphorylation, where most ATP is made.
Oxidative phosphorylation
- This stage makes most of the ATP:
- hydrogen splits into protons and energetic electrons.
- electrons pass along the electron transport chain 电子传递链, releasing energy.
- that energy pumps protons across the inner membrane.
- protons flow back through ATP synthase ATP合酶, making ATP (chemiosmosis).
- oxygen is the final electron acceptor 最终电子受体, joining electrons and protons to form water.
Chemiosmosis on the inner mitochondrial membrane
Match each term to what it means.
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Krebs strips off CO₂ and H; the reduced coenzymes feed oxidative phosphorylation, where oxygen is the final electron acceptor.
Which stage of respiration produces most of the ATP?
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Oxidative phosphorylation, using the reduced coenzymes, makes the great majority of the ATP.
In oxidative phosphorylation, the final electron acceptor is ______, which forms water.
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Oxygen accepts the electrons at the end of the chain and combines with protons to form water — this is why we need to breathe.
ATP is made as protons flow back through:
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Protons pumped across the inner membrane flow back through ATP synthase, driving ATP synthesis — chemiosmosis.
Mitochondria, built for the job
- The inner membrane is folded into cristae 嵴 — a large surface for the electron transport chain and ATP synthase.
- The matrix holds the substances and helpers for the link reaction and Krebs cycle.
The cristae of a mitochondrion are useful because they:
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The folded inner membrane (cristae) maximises the area for the electron carriers and ATP synthase.
You've got it
- Krebs cycle: acetyl + oxaloacetate → citrate → back; decarboxylation (CO₂) + dehydrogenation (reduced NAD/FAD)
- oxidative phosphorylation makes most ATP: electron transport chain pumps protons → ATP synthase (chemiosmosis)
- oxygen is the final electron acceptor → water
- cristae give a large surface; the matrix runs the link reaction + Krebs