What problem do telomeres solve and which enzyme extends them?

• A. Telomeres prevent loss of important DNA at ends; telomerase extends telomeres in germ and certain cells using an RNA template.
• B. Telomeres regulate transcription; primase extends them.
• C. Telomeres unwind DNA; helicase extends them.
• D. Telomeres repair double-strand breaks; ligase extends them.

Answer: (A)

Telomeres protect the ends of linear chromosomes from being lost or misinterpreted as DNA damage during replication, addressing the end-replication problem where DNA polymerases can’t fully copy the very ends. The enzyme that extends telomeres is telomerase, a reverse transcriptase that carries an RNA template and adds telomeric repeats to the chromosome ends, helping germ cells and some other cells maintain their length. Other enzymes listed play different roles in replication or repair (primase makes RNA primers, helicase unwinds DNA, ligase seals breaks) and do not extend telomeres. So the combination of protecting essential DNA ends and using an RNA template to elongate those ends makes this choice the best fit.