Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
Ras protein is a signalling GTPase that acts as a binary molecular switch in cellular signal transduction. Functionally, Ras is a:
Options:
(A) trimeric GTPase involved in relaying signal from cell surface to nucleus.
(B) monomeric GTPase involved in relaying signal from cell surface to nucleus.
(C) trimeric GTPase involved in regulation of cytoskeleton.
(D) monomeric GTPase involved in regulation of cytoskeleton.
Official Answer Key:
B OR D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2020 Q.12)**
**1. Governing Concept**:
- **Topic**: Cell Signaling & Small GTPases (Ras Superfamily)
- **Ras** is a canonical **monomeric small GTPase** ($\sim 21\text{ kDa}$) that operates as a molecular binary switch:
- Active when bound to GTP, inactive when bound to GDP.
- Downstream of receptor tyrosine kinases (RTKs), Ras activates the Raf-MEK-ERK (MAP kinase) cascade to relay signals from the cell surface to the nucleus, regulating gene expression and proliferation.
- In addition, Ras and related small GTPases participate in downstream cytoskeletal modulation.
- **Official GATE Status**: Both **B** (*monomeric GTPase involved in relaying signal from cell surface to nucleus*) and **D** (*monomeric GTPase involved in regulation of cytoskeleton*) were officially credited.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Ras is monomeric, not a heterotrimeric G-protein ($\text{G}\alpha\beta\gamma$).
- **Option (B) is CORRECT (Officially Accepted)**: Canonical MAPK signaling transducer from plasma membrane to nucleus.
- **Option (C) is INCORRECT**: Ras is monomeric.
- **Option (D) is CORRECT (Officially Accepted)**: Monomeric GTPase also modulating actin cytoskeletal dynamics.
**3. Final Answer**:
- **Correct Choice**: **B OR D**
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