The Calvin cycle
| English | Chinese | Pinyin |
|---|---|---|
| fixation | 固定 | gù dìng |
| rubisco | 核酮糖二磷酸羧化酶 | hé tóng táng èr lín suān suō huà méi |
| RuBP | 核酮糖二磷酸 | hé tóng táng èr lín suān |
| regeneration | 再生 | zài shēng |
| triose phosphate | 丙糖磷酸 | bǐng táng lín suān |
Building sugar from air
- The light-independent stage builds sugars in the stroma.
- It uses the ATP and reduced NADP made by the light stage.
- It runs as a cycle, in three main steps.
Step 1: Fixation 固定
- The enzyme rubisco 核酮糖二磷酸羧化酶 joins carbon dioxide to a 5-carbon molecule, RuBP 核酮糖二磷酸 (ribulose bisphosphate).
- This makes two molecules of a 3-carbon compound, GP (glycerate 3-phosphate).
The Calvin cycle: fixation, reduction and regeneration 再生
The Calvin cycle
Step around the cycle. CO₂ is fixed onto RuBP, reduced to sugar using the light-stage's ATP and NADP, and RuBP is regenerated.
In fixation, the enzyme rubisco:
Rubisco catalyses carbon fixation: CO₂ + RuBP → 2 GP.
The enzyme that joins CO₂ to RuBP in the fixation step is ______.
Rubisco is the most abundant enzyme on Earth — it fixes nearly all the carbon in the living world.
The Calvin cycle is the light-independent stage; it uses the ATP and reduced NADP made by the light-dependent stage.
It does not need light directly, but it cannot run without the ATP and reduced NADP from the light reactions.
Steps 2 & 3: Reduction and regeneration
- Reduction: GP is reduced to TP (triose phosphate 丙糖磷酸), using reduced NADP and ATP.
- Regeneration: most TP is used (with more ATP) to regenerate RuBP, so the cycle keeps running.
GP is reduced to TP using:
The reduction step uses the reduced NADP and ATP made in the light-dependent stage.
Put the steps of the Calvin cycle in order.
CO₂ is fixed onto RuBP (fixation) → GP reduced to TP (reduction) → RuBP regenerated (regeneration).
Match each step or molecule to its role.
Fix the carbon, reduce GP to sugar, then regenerate the RuBP acceptor so the cycle keeps turning.
Making useful molecules
- Some TP leaves the cycle to make carbohydrates, lipids and amino acids.
- GP can also be used to make some amino acids.
What happens to the TP that leaves the cycle?
TP that leaves the cycle builds useful molecules: carbohydrates, lipids and amino acids.
You've got it
- fixation: rubisco + CO₂ + RuBP (5C) → 2 GP (3C)
- reduction: GP → TP using reduced NADP + ATP
- regeneration: TP → RuBP (more ATP) to keep the cycle going
- some TP leaves → carbohydrates, lipids, amino acids