RuBisCO: Enzyme Specificity & Competitive Binding — NEET Biology
✅ Asked in NEET 2023Given below are two statements: (NEET 2023) Statement I: RuBisCO is the most abundant enzyme in the world. Statement II: Photorespiration does not occur in C₄ plants. Choose the most appropriate answer:
Given below are two statements: (NEET 2023) Statement I: RuBisCO is the most abundant enzyme in the world. Statement II: Photorespiration does not occur in C₄ plants. Choose the most appropriate answer:
Answer & NCERT explanation
Correct answer: C — Both Statement I and Statement II are correct
Both statements are correct. RuBisCO is indeed the most abundant enzyme in the world due to its presence in all photosynthetic organisms. Photorespiration does not occur in C₄ plants because they have CO₂ concentrating mechanisms that prevent RuBisCO from binding with oxygen.
Read more NCERT concept on the PYQ
RuBisCO that is the most abundant enzyme in the world (Do you wonder why?) is characterised by the fact that its active site can bind to both CO₂ and O₂ – hence the name. Can you think how this could be possible? RuBisCO has a much greater affinity for CO₂ when the CO₂: O₂ is nearly equal. Imagine what would happen if this were not so! This binding is competitive. It is the relative concentration of O₂ and CO₂ that determines which of the two will bind to the enzyme.
NTA tests RuBisCO's dual substrate affinity—its ability to bind both CO₂ and O₂ competitively at its active site, making it the world's most abundant enzyme. Students mistakenly think RuBisCO exclusively binds only CO₂, or assume O₂ binding is irrelevant. The key point: RuBisCO's outcome depends on the relative concentration ratio of CO₂ to O₂ in the environment, not just presence or absence. Remember: Higher CO₂:O₂ ratio favors photosynthesis (CO₂ fixation), while higher O₂ concentration favors photorespiration (O₂ fixation), reducing photosynthetic efficiency. This concept explains why C₃ plants struggle in hot, dry conditions.
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