Q.74 Match List I with List II
| LIST I | LIST II |
|---|---|
| A. Cyclin D/CDK4 B. Cyclin E/CDK2 C. Cyclin B/CDK1 D. p53 |
I. Triggers cell death II. Transition from G2 to M III. Initiation of DNA synthesis IV. G1 checkpoint |
Choose the correct answer from the options given below:
- (A)–(IV); (B)–(I); (C)–(II); (D)–(III)
- (A)–(III); (B)–(II); (C)–(IV); (D)–(I)
- (A)–(I); (B)–(II); (C)–(III); (D)–(IV)
- (A)–(IV); (B)–(III); (C)–(II); (D)–(I)
Correct Answer: (A)–(IV); (B)–(III); (C)–(II); (D)–(I)
Cyclin-CDK complexes and p53 are key regulators of the cell cycle, ensuring progression through phases like G1, S, G2, and M while preventing errors that could lead to uncontrolled division.
Option Analysis
A. Cyclin D/CDK4 → IV. G1 checkpoint
True. Cyclin D pairs with CDK4 (or CDK6) in early G1 phase to phosphorylate Rb protein, passing the G1 restriction point/checkpoint and committing the cell to division.B. Cyclin E/CDK2 → III. Initiation of DNA synthesis
True. This complex activates at the G1/S transition, fully phosphorylating Rb to release E2F transcription factors that trigger S-phase genes for DNA replication initiation.C. Cyclin B/CDK1 → II. Transition from G2 to M
True. Known as mitosis-promoting factor (MPF), Cyclin B/CDK1 peaks in late G2, phosphorylating targets to break down nuclear lamina and initiate mitosis (prophase).D. p53 → I. Triggers cell death
True. p53 acts as a tumor suppressor; if DNA damage is detected (e.g., at G1 checkpoint), it can induce apoptosis via genes like BAX or PUMA, halting faulty cells.Other Choices Incorrect
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First option mismatches B to I (Cyclin E/CDK2 doesn’t trigger death) and D to III (p53 isn’t for DNA synthesis).
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Second option mismatches A to III (Cyclin D/CDK4 is G1, not DNA synthesis), B to II (Cyclin E/CDK2 is S-phase initiation), and C to IV (Cyclin B/CDK1 isn’t G1 checkpoint).
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Third option mismatches entirely, e.g., A to I (Cyclin D/CDK4 doesn’t trigger death).
Cyclin D CDK4 G1 checkpoint and other cyclin-CDK matches are essential for cell cycle regulation, helping students ace matching questions on checkpoints, DNA synthesis, and apoptosis in competitive biology exams.
Cell Cycle Overview
The cell cycle progresses via cyclin-CDK complexes: Cyclin D/CDK4 handles G1 checkpoint by inactivating Rb; Cyclin E/CDK2 initiates DNA synthesis at G1/S; Cyclin B/CDK1 drives G2 to M transition; p53 triggers cell death on DNA damage.
Key Complex Functions
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Cyclin D/CDK4: Responds to growth factors, phosphorylates Rb for G1 progression.
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Cyclin E/CDK2: Triggers S-phase entry and DNA replication start.
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Cyclin B/CDK1: Activates mitosis entry from G2.
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p53: Monitors damage, induces apoptosis if irreparable.
Exam Tips
Focus on phase-specific pairings for questions like this—G1 (D4/E2), S (E2/A2), G2/M (B1), checkpoints (p53). Matches A-IV, B-III, C-II, D-I are standard in NCERT and standard texts.
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