Question

Which type of polymerase activity is shown by the enzyme telomerase?

• A. DNA-dependent DNA polymerase
• B. DNA-dependent RNA polymerase
• C. RNA-dependent DNA polymerase
• D. RNA-dependent RNA polymerase

Hint:

Remember the name "reverse transcriptase" for RNA-dependent DNA polymerase. Telomerase performs reverse transcription to extend the ends of chromosomes. This is a key concept in both molecular biology and cancer studies, as telomerase is often reactivated in cancer cells.

Answer 1

The Correct Option is C

Step 1: Understanding Telomerase:
Telomerase is a specialized enzyme that maintains telomere length. Telomeres are repetitive DNA sequences at the ends of chromosomes. Chromosomes shorten during cell division, and telomerase prevents this by adding telomeric repeats.

Step 2: Telomerase Mechanism:
Telomerase is a ribonucleoprotein, composed of a protein component (TERT - telomerase reverse transcriptase) and an RNA component (TERC - telomerase RNA component).
Telomerase uses its internal RNA (TERC) as a template for DNA synthesis.
- It synthesizes DNA, making it a DNA polymerase.
- It uses RNA as a template, making its activity RNA-dependent.
Therefore, telomerase is an RNA-dependent DNA polymerase, also known as a reverse transcriptase.

Step 3: Option Analysis:
- (A) DNA-dependent DNA polymerase: Synthesizes DNA using a DNA template (e.g., DNA polymerase in replication).
- (B) DNA-dependent RNA polymerase: Synthesizes RNA using a DNA template (e.g., RNA polymerase in transcription).
- (C) RNA-dependent DNA polymerase: Synthesizes DNA using an RNA template. This accurately describes telomerase.
- (D) RNA-dependent RNA polymerase: Synthesizes RNA using an RNA template (e.g., some viruses).

Step 4: Conclusion:
Telomerase synthesizes DNA using an RNA template, which is RNA-dependent DNA polymerase activity. Therefore, option (C) is correct.