C3 cycle or Calvin cycle | neet biology | class 11th biology |

Описание: C3 cycle or Calvin cycle | neet biology | class 11th biology
The Calvin cycle proceeds in three stages: (1) carboxylation, during which CO2
combines with
ribulose-1,5-bisphosphate; (2) reduction during which carbohydrate is formed at the expense of the
photochemically made ATP and NADPH; and (3) regeneration during which the CO2
acceptor ribulose-
1,5-bisphosphate is formed again so that the cycle continues.
Carboxylation: Carboxylation is the fixation of CO2 into a stable organic intermediate.
Carboxylation is the most crucial step of the Calvin cycle where CO2 is utilised for the carboxylation
of RuBP. This reaction is catalysed by the enzyme RuBP carboxylase which results in the formation
to two molecules of 3-PGA. Since this enzyme also has an oxygenation activity it would be more
correct to call it RuBP carboxylase-oxygenase or RuBisCO.
2. Reduction: These are a series of reactions that lead to the formation of glucose. The steps involve
uitlisation of 2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO2
molecule fixed. The fixation of six molecules of CO2 and 6 turns of the cycle are required for the
removal of one molecule of glucose from the pathway.
3. Regeneration: Regeneration of the CO2 acceptor molecule RuBP is crucial if the cycle is to
continue uninterrupted. The regeneration steps require one ATP for phosphorylation to form RuBP.
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