Light independent reaction

Question 1

Explain carbon dioxide fixation

Answer 1

CO2 enters the Calvin cycle, and is fixed by combining with a 5C compound called RUBP, catalyzed by RUBP carboxylase to form an unstable intermediate 6C compound. The unstable 6C compound immediately splits into half to form 2 molecules of PGA

Question 2

Explain PGA reduction

Answer 2

PGA is reduced to PGAL. The electrons for this reduction come from NADPH produced from the light-dependent reactions.
The energy for this step comes from ATP produced from the light-dependent reactions. For every 3 molecules of CO2, there are 6 molecules of PGAL but only 1 molecule of PGAL exits the cycle, and will be used by the plant cell to synthesize glucose

Question 3

Explain RUBP regeneration

Answer 3

in a complex series of reactions, the carbon skeletons of 5 molecules of PGAL are rearranged by the last steps of the Calvin cycle in to 3 molecules of RUBP.
3 more molecules of ATP from light dependent reaction used. The RUBP is now prepared to receive CO2 again, and the cycle continues