GATE BT 2019 • Q46
MCQ • 2 Marks
Section 3: Genetics, Cellular and Molecular Biology
Classical Genetics and Epistasis
Subtopic: Mendelian Genetics & Gene Interactions
Question Statement:
Which one of the following covalent linkages exists between 7-Methyl guanosine (m'G)
and mRNAs?
Options:
-
(A) 2'-3' triphosphate
-
(B) 3'-5' triphosphate
-
(C) 5'-5' triphosphate
-
(D) 2'-5' triphosphate
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2019 Q.46)**
**1. Governing Concept**:
- **Topic**: Biochemistry & Polysaccharide Glycosidic Bonds
- Identifying covalent linkages in natural biopolymers:
- Starch (amylose): $\alpha(1 \rightarrow 4)$ glycosidic bonds.
- Starch (amylopectin) / Glycogen: $\alpha(1 \rightarrow 4)$ with $\alpha(1 \rightarrow 6)$ branch points.
- **Cellulose**: Unbranched linear polymer of D-glucose linked by **$\beta(1 \rightarrow 4)$ glycosidic bonds**.
- **Chitin**: Linear polymer of $N$-acetylglucosamine (GlcNAc) linked by **$\beta(1 \rightarrow 4)$ glycosidic bonds**.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Alpha linkage found in storage carbohydrates, not structural cell wall polymers.
- **Option (B) is INCORRECT**: Beta 1-3 linkage found in callose/curdlan.
- **Option (C) [β(1→4) glycosidic linkage] is CORRECT**: The specific covalent bond forming rigid structural fibers in cellulose and chitin.
- **Option (D) is INCORRECT**: Alpha 1-6 branching linkage.
**3. Final Answer**:
- **Correct Choice**: **C**
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