Telomere Maintenance by Telomerase in Stem Cells

Steps:

• Telomeres are protective caps on chromosome ends that normally shorten during cell division due to incomplete DNA replication.
• Embryonic stem cells express high levels of telomerase, a reverse transcriptase enzyme.
• Telomerase adds telomeric DNA repeats to chromosome ends, counteracting shortening.
• This allows continuous replication without telomere loss, enabling indefinite division.

Why D is correct:

• Telomerase continuously replenishes telomeres in embryonic stem cells, maintaining their length as defined by the enzyme's role in preventing replicative senescence.

Why the others are wrong:

• A: Telomeres are maintained, not elongated beyond original length.
• B: Telomerase prevents the typical decrease seen in somatic cells.
• C: Telomeres do not erode to zero; telomerase ensures stability.

Final answer: D