The calvin Cycle

• 1. Carbon dioxide combines with a molecule of RuBP. This reaction is catalysed by RuBisCo.
• 2. RuBP becomes carboxylated by accepting a COO group. This forms an unstable intermediate six carbon compound which will immediately break down.
• 3. The product of the unstable 6 carbon compound breaking down is two molecules of GP. GP is glycerate 3 phosphate.
• 4. The GP (glycerate 3 phosphate) is reduced using protons, from reduced NADP made from the light dependent stage, to TP (triose phosphate). Energy from ATP, also from the light dependent stage, is used at this stage.
• What is the rate of how ATP from the light dependent stage is used?

  Two molecules of ATP for every molecule of carbon dioxide
• 5. for 10 of 12 triose phosphate molecules, the atoms are rearranged to regenerate six molecules of RuBP. This process requires phosphate groups. Chloroplasts contain low levels of RuBP as it is constantly converted into GP but is also continually regenerated.
• During the light dependent stage, hydrogen ions are pumped from the stroma into the thylakoid space. so the concentrations of protons in the stroma will fall and raise the pH to about 8. This pH value is optimum for RuBisCo to function.
• RuBisCo is activated by the presence of the extra ATP in the stroma
• in the daylight, the concentration of magnesium ion increases in the stroma. These ions attach to the active site of RuBisCo, which activates RuBisCo because they act as cofactors.