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 the Concept:
Telomerase is a specialized enzyme responsible for maintaining the length of telomeres, which are repetitive nucleotide sequences at the ends of linear chromosomes. Chromosomes shorten with each cell division, and telomerase counteracts this by adding telomeric repeats to the chromosome ends.

Step 2: Detailed Explanation:
Telomerase is a ribonucleoprotein, meaning it is composed of both a protein component (TERT - telomerase reverse transcriptase) and an RNA component (TERC - telomerase RNA component).
The enzyme functions by using its internal RNA component (TERC) as a template to synthesize DNA.
- It synthesizes DNA, so it is a DNA polymerase.
- It uses an RNA molecule as a template, so its activity is RNA-dependent.
Therefore, telomerase is an RNA-dependent DNA polymerase. This type of enzyme is also known as a reverse transcriptase.

Step 3: Analyzing the Options:
- (A) DNA-dependent DNA polymerase: An enzyme that synthesizes DNA using a DNA template (e.g., DNA polymerase during replication).
- (B) DNA-dependent RNA polymerase: An enzyme that synthesizes RNA using a DNA template (e.g., RNA polymerase during transcription).
- (C) RNA-dependent DNA polymerase: An enzyme that synthesizes DNA using an RNA template. This correctly describes telomerase.
- (D) RNA-dependent RNA polymerase: An enzyme that synthesizes RNA using an RNA template (e.g., found in some viruses).

Step 4: Final Answer:
The activity of telomerase is to synthesize DNA using an RNA template, which is defined as RNA-dependent DNA polymerase activity. Thus, option (C) is correct.