Light Independent Stage

Light Independent Stage

Hydrogen from reduced NADP (NADPH) and carbon dioxide is used to build organic molecules, such as glucose. ATP supplies the required energy.

Where does the LIR / Calvin cycle take place?

Stroma

1)

- Carbon fixation

CO2 is combined with 5C molecule "ribulose bisphosphate" (RuBP)

The enzyme "Ribulose bisphosphate carboxylase" (RuBisCO) catalyses the reaction and an unstable 6C intermediate is produced

What is RuBisCO completely inhibited by?

Oxygen

2)

The unstable 6C compound breaks down to form 2x 3C glycerate 3-phosphate (GP) molecules

3)

- Each GP molecule is converted to another 3C molecule, triose phosphate (TP)

- It converted by using a H atom from reduced NADP (NADPH - this is oxidation of NADPH) and energy supplied by ATP (ATP --> ADP).

- Both of these are from the LDR

4)

TP is a carbohydrate 3C sugar, and the majority of which is recycled to regenerate RuBP so that the Calvin cycle can continue.

Fixation

Carbon dioxide is fixed (incorporated into in organic molecule) in the first step

Reduction

GP is reduced to TP by the addition of hydrogen from reduced NADP using energy supplied by ATP

Regeneration

RuBP is regenerated from the recycled TP

1) Regeneration of RuBP

For 1 glucose molecule to be produced, 6 carbon dioxide molecules have to enter the Calvin cycle, resulting in 6 full turns of the cycle

2) Regeneration of RuBP

This will result in 12 TP molecules, 2 of which will be removed to make the glucose molecule

3) Regeneration of RuBP

This means 10x TP molecules are recycled to regenerate 6x RuBP molecules

4) Regeneration of RuBP

10 x 3C TP = 30 carbons

5) Regeneration of RuBP

This gives 5 x 5C RuBP = 30 carbons

6) Regeneration of RuBP

Energy is supplied by ATP for the reactions involved in the regeneration of RuBP