What is telomerase's role in protecting linear chromosomes?

• A. Repairs double-strand breaks
• B. Synthesizes the RNA primer
• C. Replicates mitochondria DNA
• D. It extends telomeres by adding repeats to the ends, protecting coding regions from erosion

Answer: (D)

Telomere length maintenance protects chromosome ends from erosion during replication. Telomeres are repetitive, noncoding sequences at the ends of linear chromosomes, acting as buffers so essential genes aren’t lost with every division. Telomerase extends these ends by adding repeats to the 3′ end, using its own RNA template, which replenishes the telomere so the coding regions remain intact as cells divide. After telomerase lengthens the end, the lagging-strand synthesis machinery can fill in the rest, and the chromosome end is kept from being treated as a DNA break. So, the key function is extending telomeres by adding repeats to the ends, protecting coding regions from erosion. The other options describe processes that are not roles of telomerase: repairing double-strand breaks, synthesizing the RNA primer for replication, or replicating mitochondrial DNA.