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Question
What conditions enable Rubirco to function as an oxygenase? Explain the ensuing process.
Solution
In the first step of the Calvin pathway, RuBP combines with CO2 to form 2 molecules of 3PGA, which is catalysed by RuBisCO.
\[\ce{RuPB + CO2 ->[RuBisCo] 2 × 3PGA}\]
RuBisCO which is the most abundant enzyme in the world is characterised by the fact that its active site can bind to both CO2 and O2 – hence the name. RuBisCO has a much greater affinity for CO2 than for O2. This binding is competitive. It is the relative concentration of O2 and CO2 that determines which of the two will bind to the enzyme.
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RELATED QUESTIONS
Even though a very few cells in a C4 plant carry out the biosynthetic – Calvin pathway, yet they are highly productive. Can you discuss why?
Calvin cycle occurs in ______.
In calvin cycle, carboxylation of RuBP fixed CO2 in number of PGA molecules
The reaction that is responsible for the primary fixation of CO2 is catalysed by ______.
\[\ce{3CO2 + 9ATP + 6NADPH + Water -> glyceraldehyde 3 – phosphate + 9 ADP + 6 NADP+ + 8 Pi}\]
Analyze the above reaction and answer the following questions:
- How many molecules of ATP and NADPH are required to fix one molecule of CO2?
- Where in the chloroplast does this process occur?
Six turns of calvin cycle are required to generate one mole of glucose. Explain.
Why is the RuBisCo enzyme more appropriately called RUBP Carboxylase-Oxygenase and what important role does it play in photosynthesis?
