Telomeres and telomerase
Introduction
Telomeres are a region of repetitive nucleotide sequences at each end of a chromosome, which protect the end of the chromosome from deterioration or from fusion with neighboring chromosomes. The enzyme telomerase, also called telomere terminal transferase, is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres. These two components play a crucial role in cell division, aging, and cancer.
Structure and Function of Telomeres
Telomeres consist of repetitive DNA sequences and associated proteins that protect the ends of chromosomes. In humans, the DNA sequence of the telomere is TTAGGG, and this sequence is repeated approximately 2,500 times. The primary function of telomeres is to prevent the degradation of genes near the ends of chromosomes by serving as a cap. This cap ensures that the cell's genetic data is accurately copied during cell division.
Role of Telomerase
Telomerase is an enzyme that adds DNA sequence repeats ("TTAGGG" in all vertebrates) to the 3' end of DNA strands in the telomere regions, which are found at the ends of chromosomes. This addition of repeated DNA sequences offsets the shortening of telomeres that occurs during DNA replication. Telomerase is active in germ cells and some adult stem cells, but is normally absent from, or at very low levels in, most somatic cells. This low level of telomerase in normal somatic cells contributes to the process of cellular aging.
Telomeres, Telomerase and Aging
The role of telomeres and telomerase in aging has been the subject of extensive research. Each time a cell divides, the telomeres become shorter. When they get too short, the cell can no longer divide and becomes inactive or "senescent" or dies. This shortening process is associated with aging, cancer, and a higher chance of death. Thus, telomeres act as the aging clock in every cell.
Telomeres, Telomerase and Cancer
Cancer cells are considered immortal because of their ability to divide indefinitely. This ability is related to the presence of active telomerase. In normal somatic cells, telomerase is absent, and telomeres shorten with each round of cell division. However, in cancer cells, telomerase is active, and it maintains the length of the telomeres, allowing the cells to divide indefinitely. This characteristic of cancer cells has made telomerase an attractive target for cancer therapeutics.