Q.42 Match the enzymes in Group I with their corresponding activity in Group II
| Group I |
Group II |
| P. Flippase |
1. Catalyzes the movement of any phospholipid across the lipid bilayer down its concentration gradient |
| Q. Floppase |
2. Catalyzes the translocation of amino-phospholipids from the extracellular to the inner leaflet |
| R. Lipase |
3. Catalyzes the translocation of membrane phospholipids from cytosolic to the extracellular leaflet |
| S. Scramblase |
4. Degradation of phospholipids from the lipid bilayer including the inner and outer leaflets |
Options:
(A) P-2, Q-3, R-4, S-1
(B) P-1, Q-2, R-3, S-4
(C) P-4, Q-1, R-2, S-3
(D) P-3, Q-2, R-4, S-1
Introduction
Cell membranes are asymmetric structures composed of phospholipids arranged in two leaflets. This asymmetry is actively maintained and regulated by specialized enzymes such as flippase, floppase, scramblase, and lipase.
This question tests your understanding of membrane lipid transport and degradation mechanisms, a common topic in cell biology, biochemistry, and competitive exams.
Correct Answer
✅ Option (A): P-2, Q-3, R-4, S-1
Detailed Explanation of Each Enzyme
1. Flippase (P → 2)
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Flippase is an ATP-dependent enzyme
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Specifically transports amino-phospholipids (like phosphatidylserine and phosphatidylethanolamine)
-
Direction: Outer (extracellular) → Inner (cytosolic) leaflet
-
Maintains membrane asymmetry
✔ Correct match: P-2
2. Floppase (Q → 3)
-
Also an ATP-dependent transporter
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Moves phospholipids in the opposite direction of flippase
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Direction: Cytosolic (inner) → Extracellular (outer) leaflet
✔ Correct match: Q-3
3. Lipase (R → 4)
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Lipase breaks down phospholipids
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Acts on phospholipids present in both inner and outer leaflets
-
Responsible for lipid degradation, not transport
✔ Correct match: R-4
4. Scramblase (S → 1)
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Scramblase is ATP-independent
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Randomly moves any phospholipid
-
Direction: Down the concentration gradient
-
Leads to loss of membrane asymmetry, especially during apoptosis
✔ Correct match: S-1
Why Option (A) Is Correct
| Enzyme |
Correct Activity |
| Flippase |
Amino-phospholipids → inner leaflet |
| Floppase |
Inner → outer leaflet |
| Lipase |
Phospholipid degradation |
| Scramblase |
Random movement down gradient |
This exactly matches Option (A).
Why Other Options Are Incorrect
Option (B)
Option (C)
Option (D)
Exam Tip
Memory Trick
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Flip-IN → Flippase
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Flop-OUT → Floppase
-
Scramble = Random
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Lipase = Breaks lipids
Conclusion
Understanding the distinct roles of membrane enzymes is essential for mastering cell biology.
The correct matching is:
✅ P-2, Q-3, R-4, S-1 (Option A)
This concept frequently appears in CSIR-NET, GATE, JAM, NEET-PG, and MSc entrance exams.
