Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
Which of the following strategies are used by cells for metabolic regulation?
[P] Phosphorylation - dephosphorylation
[Q] Allostery
[R] Feedback inhibition
Options:
(A) P and Q only
12 ---
(B) P and R only
(C) Q and R only
(D) P, Q and R
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2020 Q.49)**
**1. Governing Concept**:
- **Topic**: Molecular Cell Biology & Cellular Stress Responses
- Strategies utilized by cells to survive unfolded/misfolded protein stress in the endoplasmic reticulum (**Unfolded Protein Response, UPR**):
- Upregulation of ER chaperones (BiP/GRP78) to assist refolding.
- Global attenuation of translation initiation (via PERK phosphorylation of eIF2$\alpha$) to reduce protein load.
- Retrotranslocation of terminally misfolded proteins into the cytosol for proteasomal degradation (**ERAD**).
- Selective activation of autophagy to clear aggregated complexes.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Incomplete set of mechanisms.
- **Option (B) is INCORRECT**: Incomplete set.
- **Option (C) is INCORRECT**: Incomplete set.
- **Option (D) is CORRECT**: Comprehensive enumeration of UPR cellular survival mechanisms.
**3. Final Answer**:
- **Correct Choice**: **D**
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