72. Which statement is correct in relation of activity of telomerase?

(1) Increase with age

(2) Observed in all cancers and responsible for immortality

(3) Responsible for apoptosis but not for ageing

(4) Elongate telomeres

Introduction

Telomerase is a specialized enzyme complex that maintains the length of telomeres — the protective caps at the ends of chromosomes. Its activity is intricately linked to cellular aging, cancer progression, and genome stability. Understanding the dynamics of telomerase activity provides insights into age-related diseases and cancer biology.

What Is Telomerase Activity?

Telomerase is an RNA-dependent DNA polymerase that adds repetitive nucleotide sequences to the ends of chromosomes, compensating for the shortening that occurs during DNA replication. This activity is crucial for maintaining telomere length and, consequently, the replicative capacity of cells.

Analysis of the Statements

1. Telomerase activity increases with age

   • Incorrect. In most human somatic cells, telomerase activity is low or absent and does not increase with age. Instead, telomeres progressively shorten as cells divide, contributing to aging and cellular senescence.

2. Telomerase activity is observed in all cancers and responsible for immortality

   • Partially correct but not absolute. Telomerase activity is detected in over 85% of malignant tumors, enabling cancer cells to maintain telomere length and achieve replicative immortality. However, some cancers use alternative lengthening mechanisms, so telomerase is not universally active in all cancers.

3. Telomerase is responsible for apoptosis but not for aging

   • Incorrect. Telomerase prevents apoptosis and cellular aging by maintaining telomere length. Telomere shortening, not telomerase activity, triggers apoptosis and senescence.

4. Telomerase elongates telomeres

   • Correct. The primary function of telomerase is to add telomeric repeats to chromosome ends, thereby elongating telomeres and maintaining genome stability.

Telomerase and Aging

• Telomerase activity is generally low in most somatic cells, leading to gradual telomere shortening with each cell division.

• Shortened telomeres signal replicative senescence or apoptosis, contributing to the aging process and age-related diseases.

• Stem cells and certain immune cells retain telomerase activity to support tissue renewal.

• Studies suggest that maintaining telomerase activity or telomere length may delay aging phenotypes.

Telomerase and Cancer

• Reactivation of telomerase is a hallmark of many cancers, granting cells the ability to divide indefinitely.

• Telomerase expression correlates with tumor progression and poor prognosis in various cancers.

• Targeting telomerase is a promising therapeutic strategy in oncology.

Summary Table

Conclusion

The correct statement regarding telomerase activity is that it elongates telomeres (option 4). Telomerase plays a pivotal role in maintaining chromosome ends, thereby influencing cellular aging and cancer development. While telomerase activity is low in most normal somatic cells and does not increase with age, it is reactivated in the majority of cancers, contributing to cellular immortality. Understanding telomerase dynamics is essential for developing anti-aging and cancer therapies.

Keywords

telomerase activity, telomere elongation, aging, cellular senescence, cancer immortality, telomere shortening, replicative senescence, telomerase in cancer, genome stability, telomerase regulation

Final answer:
(4) Elongate telomeres