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Introduction:
Telomeres are an important and relatively new branch of study in science today. It has been discovered that telomeres are linked with the process of aging, as well as formation of cancer [1] [4] [5] [8]. These links give us an insight into the life of a cell, and the potential for cells to undergo immortalisation [4] [5]. In theory this knowledge could improve the quality of human life and be utilised in potential cancer treatments [4] [5] [7].

**Telomeres:**
Telomeres are repetitive strands of DNA on the ends of a chromosome [3]. Their main function is to protect the DNA and prevent the chromosome ends from fusing together [2] [3] [8]. When a cell divides it cannot completely replicate due to incomplete division, so the ends of the telomeres are lost [2] [6]. This is reflective of cell aging. When the telomeres get too short, the cell reaches a point called senescence in which it can no longer divide, and therefore dies [1]. This point is known as the Hayflick limit, and is the basis of cellular aging [1] [8].

Figure 1: Structure of a Chromosome (Picture obtained from Dahse, Fiedler and Ernst 1997)

Telomerase:
It is possible for a cell to extend its telomere by producing an enzyme called telomerase [5] [10]. This enzyme allows a telomere to produce DNA sequences and hence maintain its length [4] [7]. The cells which normally produce telomerase are gametes (sex cells), stem cells and immune cells [6] [9] [10]. Normal body cells, or somatic cells, do not usually produce telomerase [7] [8]. These cells are the cells which "age". Under certain conditions, however, these cells may produce telomerase. An example of this is cancer cells. These cells produce telomerase in order to continue dividing indefinitely, and hence become immortalised [4] [5]. Though telomerase helps cancer cells to continue to replicate, it may also be the key to learning more about how these cells work and provide new avenues into cancer treatments [4] [5] [7].

By Ashlea Norton, Josh Campe, Peter Knipler and Yong Min Kim //Last edited 11/11/2011//

References:
 [1] Aubert, G. & Landsdorp, P.M. 2008, "Telomeres and Aging", //Physiological Reviews,// vol. 88, no. 2, pp. 557-579.

[2] Autexier, C. & Lue, N.F. 2006, "The Structure and Function of Telomerase Reverse Transcriptase", //Annual Review of Biochemistry,// vol. 75, pp. 493-517.

[3] Capper, R., Britt-Compton, B., Tankimanova, M., Rowson, J., Letsolo, B., Man, S., Haughton, M. & Baird, D.M. 2007, "The Nature of Telomere Fusion and a Definition of the Critical Telomere Length in Human Cells", //Genes and Development,// vol. 21, no. 19, pp. 2508.

[4] Dahse, R., Fiedler, W. & Ernst, G. 1997, "Telomeres and Telomerase: Biological and Clinical Importance", //Clinical Chemistry,// vol. 43, no. 5, pp. 708-714.

[5] Greider, C.W. & Blackburn, E.H. 1996, "Telomeres, Telomerase and Cancer", //Scientific American,// vol. 96, no. 2, pp. 92.

[6] Hodes, R.J. 1999, "Telomere Length, Aging and Somatic Cell Turnover", //The Journal of Experimental Medicine,// vol. 190, no. 2, pp. 153-156.

[7] Shay, J.W., Zou, Y., Hiyama, E. & Wright, W.E. 2001, "Telomerase and Cancer", //Human Molecular Genetics,// vol. 10, no. 7, pp. 677-685.

[8] Wai, L.K. 2004, "Telomeres, Telomerase and Tumorigenesis - A Review", //Medscape General Medicine,// vol. 6, no. 3, pp. 19.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 80%; vertical-align: super;">[9] Wright, D.L., Jones, E.L., Mayer, J.F., Oehninger, S., Gibbons, W.E. & Lanzendorf, S.E. 2001, "Characterisation of Telomerase Activity in the Human Oocyte and Preimplantation Embryo", //Molecular Human Reproduction,// vol. 7, no. 10, pp. 947-955.

<span style="font-family: Arial,Helvetica,sans-serif; font-size: 9pt;"><span style="font-family: Arial,Helvetica,sans-serif; font-size: 80%; vertical-align: super;">[10] Zvereva, M.I., Shcherbakova, D.M. & Dontsova, O.A. 2010, "Telomerase: Structure, Functions, and Activity Regulation", //Biochemistry (Moscow),// vol. 75, no. 13, pp. 1563-1583.