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Question on Telomeres
#1
I understand the general concept of Telomeres buffering the genetic sequence, and that they degrade over time with each division of the cell. My question is: What creates and/or repairs the Telomeres in sex cells and related cells, to ensure a full amount of cell divisions for the resultant zygote? Is it Telomerase, and if so, why is the process specific to only the sexual reproduction process? If this didn't happen, wouldn't the genetic code of even sex cells degrade with every iteration meiosis? I know sex cells only divide once, however after many generations? wouldn't their DNA degrade without the protection provided by Telomeres?

I apologize for the bulk of questions, I am only trying to clarify my exact question, so as to avoid general answers that may be found online with a quick web query.

Thank you for your time and effort!
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#2
The body continually replenishes cells. As telomeres shorten, eventually old cells die by apoptosis or become senescent. This would normally be after about 50-70 cell divisions, although this can vary between cell types. There are many scholarly articles examining the connections between telomere length, telomere shortening and apoptosis or senescence. Telomeres are repeated sequences at the ends of strands of DNA that protect the DNA from degradation; they consist of repeats of the sequence TTAGGG on one strand paired with AATCCC on the other strand. Telomere shortening is associated with normal aging.

As I understand it, your question relates specifically to sex cells and how telomeres are protected from shortening in order to allow a sufficient number of cell divisions. It appears that sex cells can activate the enzyme telomerase in order to protect against telomere shortening and ensure sufficient cell divisions. This effectively makes sex cells ‘immortal’. Telomerase is an enzyme that adds repeat sequences to the end of genes. Telomerase is active at a much higher level in sex cells, which are passed on from one generation to the next, than in somatic cells. If the DNA in sex cells degraded after only a small number of cell divisions, the species could not survive. As you suggest in your original question, without telomerase, the DNA in sex cells would degrade too quickly. However, with somatic cells, it is desirable that old cells be cleared by apoptosis and senescence, to be replaced with new cells.

High telomerase levels is a strategy that has been hijacked by some tumour cells, making telomerase and telomere length subjects of interest to cancer researchers. The human telomerase gene TERT was mapped in 2013 (Bojesen et al, 2013) by researchers with an interest in its role in breast and ovarian cancer.
I hope this helps with your question; if not, please get back on to the forum. Below are some references and sources that may help further.

Stig E Bojesen et al. Multiple independent variants at the TERT locus are associated with telomere length and risks of breast and ovarian cancer. Nature Genetics, 2013; 45 (4): 371 DOI: 10.1038/ng.2566

http://learn.genetics.utah.edu/content/c...telomeres/

http://www.lef.org/magazine/mag2009/aug2...ion_01.htm

http://www.sciencedaily.com/releases/201...133341.htm

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#3
That was exactly my question, thank you for your reply. I was imagining as much about the presence of telomerase, however I found the question curious enough to merit a detailed answer! I will definitely be exploring this subject more in depth.

Thanks again
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#4
(07-15-2014, 10:42 PM)zuzufarah Wrote: That was exactly my question, thank you for your reply. I was imagining as much about the presence of telomerase, however I found the question curious enough to merit a detailed answer! I will definitely be exploring this subject more in depth.

Thanks again

You're welcome :-)
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