Telomerase adds hexanucleotide repeats (TTAGGG) to chromosomal ends to prevent replicative senescence. In which of the following scenarios is telomerase activity pathologically re-activated?

• A Approximately 85-90% of human malignant tumors, enabling replicative immortality ✓
• B Dyskeratosis congenita, an inherited telomere maintenance disorder
• C Normal stem cells in the bone marrow and germ cells as a physiological mechanism
• D Neurons during long-term potentiation to protect against oxidative DNA damage

Explanation

Telomerase is silenced in most somatic cells but is re-activated in approximately 85-90% of human cancers, where TERT (telomerase reverse transcriptase) promoter mutations are particularly common. This re-activation prevents telomere shortening and enables replicative immortality, one of the hallmarks of cancer. Dyskeratosis congenita involves dysfunctional telomere maintenance (mutations in dyskerin, TERT, TERC) causing premature telomere shortening, not re-activation. Normal stem cells and germ cells do express low-level telomerase physiologically.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.