Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
Which of the following statements are CORRECT about eukaryotic cell cycle?
[P] CDKs can phosphorylate proteins in the absence of cyclins
[Q] CDKs can be inactivated by phosphorylation
[R] Degradation of cyclins is required for cell cycle progression
[S] CDKs are not involved in chromosome condensation
Options:
(A) S ...→ W→ x → Y→ Z
Z2
Z4
(B) S
(C) S
..→ W→ X → Y→ z
Z3
Z2
Z4
(D) S
•..→ W→ X→ Y→ Z
Z4
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2020 Q.39)**
**1. Governing Concept**:
- **Topic**: Cell Biology & Cytoskeletal Filaments
- Evaluating cytoskeletal filaments:
- **[P] Microtubules**: Polymers of $\alpha/\beta$-tubulin heterodimers; polarized ($+$ and $-$ ends) showing dynamic instability $\rightarrow$ **CORRECT**.
- **[Q] Microfilaments (Actin filaments)**: Polymers of globular G-actin forming polarized two-stranded helical F-actin $\rightarrow$ **CORRECT**.
- **[R] Intermediate filaments**: Non-polarized, rope-like structural fibers assembled from apolar anti-parallel tetramers (e.g., keratins, vimentin, lamins); lack nucleotide triphosphate binding $\rightarrow$ **CORRECT**.
- All statements characterizing their structural polarity and subunit composition are correct (Option D).
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Incomplete statement set.
- **Option (B) is INCORRECT**: Incomplete set.
- **Option (C) is INCORRECT**: Incomplete set.
- **Option (D) is CORRECT**: All cytoskeletal structural and kinetic assertions are verified.
**3. Final Answer**:
- **Correct Choice**: **D**
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