Which statement about telomerase activity in human somatic cells is true?

Which statement about telomerase activity in human somatic cells is true?

• A. Telomerase actively lengthens telomeres in most somatic cells.
• B. Telomerase is completely absent in all human cells.
• C. Telomerase is active only during mitosis.
• D. Telomerase is usually inactive in somatic cells, leading to progressive telomere shortening.

Answer: (D)

Telomeres protect chromosome ends and tend to shorten with every cell division in human somatic cells. Telomerase can lengthen telomeres by adding repetitive DNA, but its activity is largely off in ordinary somatic cells. Because telomerase is usually inactive, telomeres shorten progressively as cells divide, which contributes to cellular aging. Telomerase is active in cells that require long-term replication, such as germ cells and some stem cells, and it is often reactivated in many cancer cells to maintain telomere length. The statements claiming telomerase lengthens telomeres in most somatic cells, or that it is completely absent in all human cells, aren’t accurate. It isn’t restricted to mitosis; when present, telomerase activity aligns with the replication process to preserve telomeres rather than being limited to a single phase.

Telomeres protect chromosome ends and tend to shorten with every cell division in human somatic cells. Telomerase can lengthen telomeres by adding repetitive DNA, but its activity is largely off in ordinary somatic cells. Because telomerase is usually inactive, telomeres shorten progressively as cells divide, which contributes to cellular aging.

Telomerase is active in cells that require long-term replication, such as germ cells and some stem cells, and it is often reactivated in many cancer cells to maintain telomere length. The statements claiming telomerase lengthens telomeres in most somatic cells, or that it is completely absent in all human cells, aren’t accurate. It isn’t restricted to mitosis; when present, telomerase activity aligns with the replication process to preserve telomeres rather than being limited to a single phase.