Question

Give an account of carboxylation ($C{O}_2$ fixation) stage of Calvin cycle.

Answer 1

Calvin cycle was discovered by Melvin Calvin while radioactive studies of alga. It occurs in all photosynthetic plants whether they have $C_3$ or $C_4$ pathway. Calvin cycle can be described under three stages: Carboxylation, reduction and regeneration.

Carboxylation is the first step of Calvin cycle. It is the fixation of $C{O}_2$ into a stable organic intermediate. In this, $C{O}_2$ is utilised for the carboxylation of RuBP. This reaction is catalysed by the enzyme RuBisCO and it results in the formation of two molecules of 3-PGA (3-Phosphoglyceric acid). It is the first stable product of photosynthesis.