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 sequences replenishes the telomere 'end cap' of the DNA. Without telomerase, the telomeres of dividing cells progressively shorten, leading to cell death (senescence) or cancer. In humans, telomerase is present in fetal tissues, adult germ cells, and also in tumor cells. Telomerase activity is regulated during development and has a very low, almost undetectable activity in somatic (body) cells. This is because telomerase is not expressed in most somatic cells, or is expressed at a level that is unable to maintain telomere length.

Structure

Telomerase is a ribonucleoprotein that contains a RNA component and a protein component. It synthesizes short segments of DNA, which are repeated to form the telomere. The RNA component serves as a template for the telomere repeat and the protein component (known as telomerase reverse transcriptase, or TERT) is the catalytic subunit of the enzyme.

Function

The primary role of telomerase in cells is to maintain the length of telomeres, which allows cells to divide without losing important DNA from the ends of chromosomes. In humans, the rapid cell division in the embryo is facilitated by the expression of telomerase. In adult tissues, telomerase is generally repressed, with exceptions in certain types of cells that need to divide regularly, such as blood cells and germ cells.

Clinical significance

Telomerase has been the focus of much research in the field of aging and cancer. In cancer cells, telomerase is often activated, which allows these cells to divide indefinitely without undergoing senescence or apoptosis. This has led to the development of therapies that target telomerase in cancer cells. On the other hand, the lack of telomerase activity in most somatic cells leads to telomere shortening and can limit the lifespan of the cell, contributing to aging and age-related diseases.

See also

• Telomere
• Aging
• Cancer
• DNA replication
• Chromosome

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