The Calvin cycle
Introduced| English | Meaning |
|---|---|
| fixation/fɪkˈseɪʃn/ | In photosynthesis, building carbon dioxide into an organic molecule by RuBisCO. |
| rubisco/ruːˈbɪskəʊ/ | rubisco |
| RuBP/ruː ˌbiːˈpiː/ | RuBP |
| regeneration/riːˌdʒenəˈreɪʃn/ | TP → RuBP (more ATP) to keep the cycle going. |
| triose phosphate/ˈtraɪəʊs ˈfɒsfeɪt/ | triose phosphate |
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Rubisco catalyses carbon fixation: CO₂ + RuBP → 2 GP.
The enzyme that joins CO₂ to RuBP in the fixation step is ______.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
The reduction step uses the reduced NADP and ATP made in the light-dependent stage.
Put the steps of the Calvin cycle in order.
Difficulty 3/5 · 200 coins + a small bonus on first completion today
CO₂ is fixed onto RuBP (fixation) → GP reduced to TP (reduction) → RuBP regenerated (regeneration).
Match each step or molecule to its role.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
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?
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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