Immortalization of malignant cells requires maintenance of telomere length despite repeated division. Which enzymatic activity accomplishes this in approximately 90% of human cancers?
- A Reverse transcriptase activity of telomerase extending the 3' end using its own RNA template ✓
- B RNA-dependent RNA polymerase activity copying the telomeric strand directly
- C DNA ligase I-mediated joining of telomeric fragments recycled from senescent cells
- D Topoisomerase II-mediated relaxation allowing conservative replication of telomeres
Correct answer: A. Reverse transcriptase activity of telomerase extending the 3' end using its own RNA template
Explanation
Telomerase contains an RNA template and the catalytic reverse transcriptase subunit hTERT; it extends the 3' G-rich telomeric overhang, compensating for the end-replication problem. Somatic cells repress hTERT, but most cancers reactivate it, conferring unlimited replicative potential. Telomerase is not an RNA-dependent RNA polymerase, and no ligase or topoisomerase mechanism maintains telomeres in this way.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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