Wednesday, 21 March 2012

What do Aglets have to do with Genetics?


Christopher Timmins
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BScience                                              BIOL1020 Blog Assisnment.

What do Aglets have to do with Genetics?
What is an ‘Aglet’? An aglet is defined asa metal tag or sheath at the end of a lace used for tying, as of a shoelace.”  (Dictionary.com 2012)  
How does this fit into a genetics context? The Hayflick limit, discovered by Prof. Lenhard Hayflick in 1961, shows that cells can only divide a specific number of times before ‘ageing’ to the point of cell death. It took until 1990 to realize why this limit exists when Calvin Harley at McMaster University and Carol Greider at Cold Spring Harbor Laboratory found that there is a fragment on the end of DNA that shortens with every cell cycle and this is what causes the Hayflick limit. Although they did not yet know what this segment might be. (telomeres.net 2011/2012)
 When DNA replicates it is found that a small potion on the strand end cannot be copied due to no 3’ carbon being available to add a nucleotide to, this leads to the strand becoming progressively shorter on each occasion that DNA is reproduced. Therefore, it appears our genetic code needs it’s own ‘aglet’ and such a device exists, these have been named after the Greek nouns ‘telos’ and ‘meros’ or ‘end part’ hence; telomeres. (Reece etal 2011 p322)
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Telomeres contain no explicit genetic sequence and hence do not code for any particular proteins, and this is the secret to how they perform their function. Consisting of a short strand of nucleotides that repeats itself, possibly many times, this is the section of DNA that is shortened instead of the precious protein sequencing genes. (Reece etal 2011 p323) Short term postulation on this leads an idea of a ‘biological clock’, that this mechanism might be linked directly to ageing and a possible answer to the ‘fountain of youth’ itself! If this shortening could somehow be halted or even reversed, could this lead to longer life?
A further question arises out of this however, if our sex cells (sperm & ova) are progressively shortened in this manner, would there not be a potential loss of genetic information? This idea lead to a discovery by Australian scientist Elizabeth Blackburn and Carol Greider of ‘telomerase’ the enzyme that catalyses creation of telomere DNA, and it is this medium that  maintains germ cell total length, including full length telomeres, for passing on to offspring. (Blackburn Lab 2011)
Extended tissue life might appeal to our utopian human urges; however, a more practical use of telomerase knowledge is it’s implications in disease. Telomerase does not function in non-sex cells as it does in eukaryotic germ cells, it still shortens with replication after mitosis. It is believed that it is this function that controls cell division from continuing unchecked and thus becoming malignant. Conversely, the short telomeres have also proven to create instability, which has an opposing effect, creating cancerous cells. This has been shown by experiment, “In vivo, mice models have indisputably shown both the protective and the promoting role of very short telomeres in cancer development.” (Arturo Londono-Vallejo 2007)
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A - Germ cell, control.
B- Cell containing stem cell compartments.
C- Somatic cell (&In Vitro).


Even with this limited knowledge, profiteers have sort to pray on the suggestive human psyche. Products such as fad diets that recommend cycling of telomerase activation and inhibition by use of ‘dietary polyphenols’ or supplements including astragalus extract, cyloastragnol, colostrum and even a spray of IGF-1 liposomal are being peddled as ‘life extension’ options.  (Life Extention 1995-2012) For the future of genetic research, care must be taken to utilize breakthroughs in a pragmatic manner and to remain diligent in their assessment.



Reference List
. Blackburn Lab, University of California, San Francisco 2012. biochemistry.ucsf.edu/labs/blackburn  viewed 10Mar2012
. Dictionary.com 2012 dictionary.reference.com viewed 17Mar 2012
. J. Arturo Lonono-Vallejo 2007 Telomere instablilty and cancer. Biochimie vol.90, issure1, January 2008 pp73-82.
. Reece, Meyers, Urry, Cain, Wasserman, Minorsky, Jackson and Cooke, 2011, Campbell Biology, Ninth Ed., (Australian Version) Pearson Education Inc. United States
. Telomeres.net 2011/2012 telomeres.net/why-do-our-bodies-age/#more-276 viewed 10 Mar2012

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