The role of telomeres

Telomeres are protective sequences of non-coding DNA found at the ends of chromosomes. They are often compared to the plastic tips on shoelaces due to their protective function. Their structure consists of short base sequences repeated many times, such as 'TTAGGG' repeated up to a thousand times. One strand of the telomere DNA is rich in guanine (G), and the other is rich in complementary cytosine (C). They can be observed when chromosomes are stained appropriately.

The primary role of telomeres is to prevent the loss of vital genetic information during DNA replication. During the S phase of the cell cycle, when a cell replicates its DNA, the copying enzyme (DNA polymerase) cannot fully replicate the very ends of the DNA strands. If these ends contained essential genes, this information would be progressively lost with each subsequent cell division, eventually leading to cell death. Telomeres act as a "buffer" region of non-essential DNA, ensuring that no important coding sections are left out of the replication process.

To counteract this shortening, an enzyme called telomerase adds additional bases to the telomeres during each cell cycle, effectively "topping up" their length. This mechanism allows for the continued replication of cells without the loss of genes.

The role of telomeres is particularly significant in understanding aging and cancer:

• Aging: In many specialized or fully differentiated cells, telomerase is not active or does not "top up" the telomeres. Consequently, with each cell division, their telomeres progressively shorten. Once the telomeres become too short, the vital coding DNA is no longer protected, which can lead to cell death. This progressive shortening of telomeres and the resulting limit on cell division is considered one of the mechanisms of aging. Studies have shown that telomere length generally decreases with age, and factors like high BMI and smoking are associated with reduced telomere length.

• Cancer: Cancer cells are often described as "immortal" because they can divide repeatedly and uncontrollably. This immortality is achieved because cancer cells typically renew their telomeres after each division using the telomerase enzyme, unlike normal cells that would eventually reach a limit on their divisions. This uncontrolled division leads to the formation of a mass of cells called a tumour, and if the tumour invades surrounding tissue, it is defined as cancer. Cancer treatments are often designed to control the rate of cell division in tumour cells by disrupting the cell cycle. Research into inactivating telomerase in cancer cells is explored as a way to prevent their unlimited division and subsequent tumour growth.

Mitosis is a precisely controlled process, and the cell cycle, including the replication of DNA during interphase, is regulated by genes. Mutations in these controlling genes can lead to uncontrolled cell division and the formation of tumours and cancers.