Structures and Roles of Telomeres

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Structures and Roles of Telomeres
Telomeres are essential structures in eukaryotic cells. Through repeat nucleotide sequencing of TTAGGG and their six associated protein complexes, they provide a “cap” over the rest of the chromosome, which protects the genetic material contained within the chromosome from instability1. Without the telomere structures, chromosomes are prone to tearing due to the action of nucleases and other damaging components within the nucleus. Torn chromosomes prove to be unstable, often fusing end-to-end or rearranging. The result can be catastrophic for the cell and eventually bring about cellular death.2 Consequently, telomeres are essential to cellular homeostasis.
In many cells, telomere length decreases with each replication. Because of this phenomenon, the cell has a limited number of divisions before apoptosis occurs. The number of divisions a cell can undergo before apoptosis ensues is known as the Hayflick limit3. The Hayflick limit states that there are about 50 generations of cellular division within each cell before cellular proliferation ceases due to apoptosis3. Therefore, telomere length has a direct correlation to how many times a cell divides. Once the telomeres are too short to protect the rest of the chromosome, degradation can occur. This creates a barrier to cellular immortality. Telomerase can help remove that barrier by its reverse transcriptase action4.
Composition and Function of Telomerase
Telomerase is a ribonucleoprotein DNA polymerase that catalyzes the lengthening of DNA on telomeres5. It accomplishes this by adding repetitive sequences of nucleic acid that are abundant in guanine2. Human telomerase consists of two major complexes, one being human telomerase reverse ...

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...Bache Nicolai. Robinson Phillip J. Reddel Roger R. Protein composition of catalytically active human telomerase from immortal cells. Science 2007:352:1850-1853.
7Mason Mark. Schuller Anthony. Skordalakes Emmanuel. Telomerase structure function. Current Opinion in Structural Biolog. 2011:21(1):92-100.
8Friedman K L. Cech TR. Essential functions of amino terminal domains in the yeast telomerase catalytic subunit revealed by selection for viable mutants. Genes Dev. 1999:13(21):2863-2874.
9Hengesbach Martin. Akiyama Benjamin M. Stone Michael D. Single-molecule analysis of telomerase function and structure. Current Opinion in Structural Biology. 2011:15(6):845-852.
10Podlevsky Joshua D. Chen Julian. It all comes together at the ends: Telomerase structure, function and biogenesis. Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis. 2012:730(1-2):3-11.

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