Approximately 90 percent of human tumours maintain telomere length through expression of telomerase. Which statement correctly describes the enzymatic activity of telomerase?

• A A DNA-dependent DNA polymerase that fills the gap left after primer removal on the lagging strand
• B An RNA-dependent DNA polymerase that adds TTAGGG repeats using its own intrinsic RNA template ✓
• C A DNA ligase that directly joins the blunt ends of sister chromatids at the telomere
• D An ATP-dependent helicase that unwinds telomeric G-quadruplex structures

Explanation

Telomerase is a specialized reverse transcriptase. Its catalytic subunit hTERT copies the template region of its own integral RNA component (hTR or TERC) to add hexameric TTAGGG repeats onto the 3' overhang, solving the end-replication problem that erodes telomeres each division. The key point against option A is that the template is RNA carried within the enzyme itself, so telomerase is RNA-dependent, unlike conventional DNA-dependent DNA polymerases that cannot fully replicate linear chromosome ends.

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

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Written and medically reviewed by the StethoPrep medical team.