Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYPhotosynthesis in Higher Plants5 Marks
Question
What conditions enable RuBisCO to function as an oxygenase? Explain the ensuing process.
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Answer
Carboxylation is the most crucial step of Calvin cycle, which involves the fixation of $\mathrm{CO}_2$ into a stable organic intermediate. Ribulose 1, 5-bisphosphate combines with $\mathrm{CO}_2$, and fixes it to a stable organic intermediate 3C compound called 3-phosphoglycerate ( 2 molecules). This reaction is catalysed by the enzyme RuBisCO (RuBP Carboxylase-Oxygenase). Since, this enzyme has high affinity for oxygen, it shows oxygenation activity when the $\mathrm{CO}_2$ concentration decreases. During high temperature, the RuBP binds to $\mathrm{O}_2$ and act as oxygenase enzyme, this forces $\mathrm{CO}_2$ to enter $\mathrm{C}_2$ cycle thus leading to photorespiration and loss of $\mathrm{CO}_2$.
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