Senescence is the failure of cells to divide due to shortened telomeres that result in aging.

As organisms age, changes occur in both molecular and cellular structures that result in metabolism disruption and, eventually, death. Senescence, or biological aging, occurs as these changes build up. It results in the failure of cells to divide. Telomeres prevent the loss of genetic information from the ends of chromosomes and help prevent the DNA from unraveling. However, they are difficult to replicate, so they shorten during each round of DNA synthesis. As the telomeres become too short, the cell can no longer replicate. The shortening of the telomeres that occurs during normal aging is controlled by the activity of specialized enzyme telomerase. This enzyme is a reverse transcriptase that can synthesize the ends of chromosomes, preventing senescence. Although telomerase is ordinarily active in cells, it is commonly expressed in human cancer cells that may play a role in cancer cell survival.

Cells that undergo cell division shorten their telomeres because most somatic cells do not make telomerase. This means that telomere shortening is associated with aging. Aging is complex and often involves not only cellular senescence but also the accumulation of chemical and environmental insults over time.

Key Points

• Senescence is the result of multiple molecular and metabolic processes, most notably the shortening of telomeres during cell division.

• Some cells express enzyme telomerase, which can synthesize the ends of chromosomes, preventing senescence. 

• The shortening of the telomeres that occurs during normal aging is controlled by the activity of specialized enzyme telomerase.

• Cells that undergo cell division shorten their telomeres because most somatic cells do not make telomerase.

• Telomerase allows for cells to divide continually and may play a role in the survival of cancer cells.

• Aging is complex and usually involves not only cellular senescence but also the accumulation of chemical and environmental insults over time.

Key Terms

senescence: the loss of a cell’s power of division and growth

telomeres: a compound structure at the end of a chromosome

telomerase: a region of repetitive sequences at each end of eukaryotic chromosomes

somatic cells: any cell of a living organism other than the reproductive cells