Subtopic: Fundamentals of Downstream processing (chromatography, filtration)
Question Statement:
Correctly match the Enzyme with its respective Function.
Enzyme Function
P. Gyrase 1. Removes a damaged base by cleaving the bond
between sugar and base
Q. Deadenylase 2. Provides a swivel allowing one DNA strand to rotate
around the other
R. Glycosylase 3. Catalyses bond formation between 3′-OH and
5′-phosphate end of nucleotides in duplex DNA
S. DNA ligase 4. Is an exoribonuclease that removes the poly(A) tail
Options:
(A) P-2; Q-4; R-1; S-3
(B) P-1; Q-4; R-2; S-3
(C) P-2; Q-1; R-4; S-3
(D) P-3; Q-2; R-1; S-4
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.40)**
**1. Governing Concept**:
- **Topic**: Cell Biology & Mitochondrial Apoptotic Pathway (Intrinsic Pathway)
- The intrinsic (mitochondrial) apoptotic pathway is regulated by Bcl-2 family proteins:
- Pro-apoptotic BH123 pore-formers (**Bax** and **Bak**) oligomerize in the mitochondrial outer membrane to cause **MOMP (mitochondrial outer membrane permeabilization)**.
- **Cytochrome c** is released from the intermembrane space into the cytosol.
- Cytosolic cytochrome c binds **Apaf-1 (Apoptotic Protease Activating Factor-1)** in the presence of dATP/ATP, assembling into a heptameric wheel-like complex called the **apoptosome**.
- The apoptosome recruits and activates the initiator caspase, **Procaspase-9**.
- Active Caspase-9 cleaves and activates executioner caspases (**Caspase-3 and Caspase-7**).
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Caspase-8 is the initiator caspase of the extrinsic (death receptor) pathway, activated by DISC.
- **Option (B) is CORRECT**: Cytochrome c binds Apaf-1 to assemble the apoptosome, which activates initiator Caspase-9.
- **Option (C) is INCORRECT**: Cytochrome c does not directly activate Caspase-3 without assembling the Apaf-1 apoptosome first.
- **Option (D) is INCORRECT**: Bcl-2 is anti-apoptotic and prevents cytochrome c release.
**3. Final Answer**:
- **Correct Choice**: **B**
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