CO₂ Fixation & RuBisCO Role — NEET Biology
📚 Practice ConceptCarboxylation – 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 of 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.
Which of the following statements are correct regarding the Calvin Cycle and related processes in photosynthesis? S1: Carboxylation in the Calvin cycle involves the fixation of CO₂ to RuBP, a 5-carbon ketose sugar, catalyzed by the enzyme RuBisCO in the stroma. S2: For every CO₂ molecule fixed in the Calvin cycle, 3 ATP and 2 NADPH molecules are consumed during the reduction and regeneration phases. S3: In C4 plants, the enzyme RuBisCO is primarily located in the mesophyll cells, where it catalyzes the primary CO₂ fixation. S4: Photorespiration, catalyzed by RuBisCO's oxygenase activity, forms a 2-carbon phosphoglycolate and does not lead to the synthesis of sugars or ATP. S5: The biosynthetic phase of photosynthesis, also known as the Calvin cycle, is directly light-dependent and requires the presence of light for its enzymatic reactions to proceed.
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