Light Independant Reactions(Calvin cycle)

What are the key steps of the Calvin cycle?

1. CO₂ combines with RuBP (5C), catalysed by RuBisCO, forming an unstable 6C compound that splits into two molecules of GP (3C). (FIXATION)

2. GP is reduced to TP using ATP and reduced NADP.(REDUCTION)

3. Some TP is used to make glucose and other organic molecules.

4. Most TP is used to regenerate RuBP, using ATP.(REGENERATION)

What is RuBisCO?

Ribulose bisphosphate carboxylase, the enzyme that fixes CO₂ by catalysing its combination with RuBP.

What happens to the TP produced?

Some is converted to carbohydrates, lipids (via glycerol and fatty acids) and amino acids (with nitrate). The rest is used to regenerate RuBP.

How many carbons are in RuBP, GP and TP?

RuBP has 5, GP has 3 and TP has 3.

Why does the Calvin cycle stop in the dark?

No ATP or reduced NADP is being made by the light-dependent reaction, so GP cannot be reduced to TP and RuBP cannot be regenerated.

What happens to the levels of GP, TP and RuBP if light intensity drops?

GP rises, because less ATP and reduced NADP are available to convert it. TP and RuBP fall, because TP is no longer being made and RuBP is not regenerated.

What happens to the levels of GP and RuBP if CO₂ concentration drops?

GP falls, because less is being made. RuBP rises, because it is not being used to fix CO₂ but is still being regenerated.