What is the role of telomerase in maintaining telomeres?

• A. Telomerase shortens telomeres
• B. Telomerase repairs double-strand breaks in DNA
• C. Telomerase unwinds telomeres during replication
• D. Telomerase extends telomeres by using its RNA template to add repetitive sequences

Answer: (D)

The main idea here is how telomerase maintains chromosome ends by adding DNA repeats. Telomerase is a ribonucleoprotein that carries its own RNA template. This RNA template provides the sequence that will be copied back into DNA to create new telomeric repeats. Using its reverse transcriptase activity, telomerase extends the 3′ end of the telomere by adding repetitive sequences (in humans, TTAGGG). This elongation counters the end-replication problem, allowing chromosomes to be replicated without losing essential genes. It isn’t primarily a repair enzyme for double-strand breaks, nor does it unwind DNA during replication. Its job is to extend telomeres using its RNA template to add those repetitive sequences.