Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
Which of the following statements is/are true about telomerase?
Options:
(A) Telomerase has 5′-3′ DNA-dependent DNA polymerisation activity
(B) Telomerase has 5′-3′ RNA-dependent DNA polymerisation activity
(C) Telomerase contains an RNA subunit
(D) Telomerase has 3′-5′ DNA-dependent DNA polymerisation activity
Official Answer Key:
B;C
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.52)**
**1. Governing Concept**:
- **Topic**: Molecular Biology & Chromosome End Replication (Telomerase)
- **Telomerase** is a specialized ribonucleoprotein (RNP) reverse transcriptase that solves the end-replication problem of linear eukaryotic chromosomes:
- Consists of a catalytic protein subunit **TERT (Telomerase Reverse Transcriptase)** and an integral RNA component **TERC (Telomerase RNA Component)**.
- TERC provides an internal RNA template (e.g. $3'-\text{AAUCCC}-5'$ in humans) that base-pairs with the $3'$ overhang to direct elongation of telomeric tandem repeats ($5'-\text{TTAGGG}-3'$).
- Extends the $3'$ single-stranded overhang of the telomere, which is subsequently converted to duplex DNA by standard lagging-strand synthesis (DNA Polymerase $\alpha$-primase).
**2. Option Analysis**:
- **Option (A) [It contains an internal DNA template] is INCORRECT**: Telomerase contains an internal **RNA** template (TERC), not a DNA template.
- **Option (B) [It is a reverse transcriptase] is CORRECT**: Its catalytic protein subunit (TERT) uses an RNA template to synthesize DNA, functioning as an RNA-dependent DNA polymerase.
- **Option (C) [It extends the 3' end of the telomeric DNA strand] is CORRECT**: Telomerase specifically adds tandem nucleotide repeats to the 3'-hydroxyl terminal overhang of the G-rich telomeric strand.
- **Option (D) [It extends the 5' end of the telomeric strand] is INCORRECT**: DNA polymerases and reverse transcriptases synthesize exclusively in the $5' \to 3'$ direction and cannot extend 5' ends.
**3. Final Answer**:
- **Correct Options**: **B, C**
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.