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<p>Week11</p>
<pstyle="text-align: center;"><span style="font-size:14px"><strong>Why do comparing telomere length and telomerase activity between species not much show any tendency? </strong></span></p>
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<pstyle="text-align: center;"> Chaeeun Lee</p>
<p><span style="font-size:14px"><strong> Abstract</strong></span></p>
<pstyle="margin-left: 40px;"> Telomere is the parts which is located at each ends of chromosomes. As DNA replicates, the end part become shorten. So, this part can protect the end parts of chromosome. As time goes by, telomere length became shorter because somatic cells do not activate telomerase which generate the sequence of telomere. By this mechanism, nowadays, telomere length and the activity of telomerase is researched to learn about aging. However, as seeing some papers there are not much relevance between telomere length and life span when comparing different species. Rather, life span and telomere length are inversely proportional. So, I wonder why this result came out.</p>
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<p><span style="font-size:14px"><strong> Introduction </strong></span></p>
<pstyle="margin-left: 40px;"> When considering just one species, longer telomere length can mean longer life. According to paper ‘Telomere length in early life predicts lifespan’, we can predict life span by using telomere length in early life and seeing their result, longer telomere means longer life. Also, there are some biologically immortal animals, and they activate their telomerase in most of their cell even in adult stage. However, when comparing different species, the activity of telomerase is not much related with their life span. Furthermore, telomere lengths are even inversely proportional to their life spans. Therefore, finding difference between species and their relevance with telomere is needed.</p>
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<p><span style="font-size:14px"><strong> Discussion</strong></span></p>
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<pstyle="margin-left: 40px;"><span style="font-size:12px"><strong> Difference between land life and sea life</strong></span></p>
<pstyle="margin-left: 40px;"> Among the biologically immortal organisms, most of them are sea life such as jelly fish, lobsters, turtles and Rougheye rockfish. Therefore, we thought about the difference between sea life and land life.</p>
<pstyle="margin-left: 40px;"> To begin with, the main difference is sun light. As animals began to live in land, they are exposed to sun light. Also, UV light can damage the DNA of land animals. So, land animals become aged and damaged from sunlight as time goes by because telomere cannot recover the UV damaged site. In other words, they are eventually aged even if they activate the telomerase to elongate telomere length. Therefore, land life might not require longer telomere and the higher activity of telomerase. For example, in case of lobsters, they express telomerase as adults through most tissue but for vertebrates, it is generally absent from adult stages of life.</p>
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<pstyle="margin-left: 40px;"><span style="font-size:12px"><strong> Body Temperature</strong></span></p>
<pstyle="margin-left: 40px;"> Second concern is the difference between homeotherm and cold- blood animals. Homeotherm should maintain their body temperature and generate heat. In other words, they have to use enzymes and need metabolic systems. Consequently, more chemical reactions occur in their body and it leads to oxidative damage in the DNA. This kind of damage cannot be recovered by telomere and telomerase. Rather, the action of telomerase can bad for damaged DNA because it can cause cancer. Therefore, to adapt as homeotherm, they might have short telomeres and repressed activity of telomerase.</p>
<pstyle="margin-left: 40px;"> For example, Ancestral placental mammals which is homeotherm, had short telomeres and repressed telomerase. While, Aquatic poikilothermic species which is not homeotherm, have short telomeres but they express telomerase in many of their tissues.</p>
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<pstyle="margin-left: 40px;"><span style="font-size:12px"><strong> Body size and cancer problem</strong></span></p>
<pstyle="margin-left: 40px;"> According to paper, ‘Comparative biology of mammalian telomeres: hypotheses on ancestral states and the roles of telomeres in longevity determination’, activity of telomerase is related with body mass but not much related with life span. Also, large animals suppress the activity of the telomerase. So it might be related with cancer problem.</p>
<pstyle="margin-left: 40px;"> In case of large species by considering the number of cell, they have more chance to get cancer because they have more cells than small species. Also, the large activity of telomerase can help causing tumor. Therefore, large animal might have to prevent the activity of telomerase to prevent causing cancer. For example, as seeing some papers (reference), it is said that large species tend to have short telomeres and they repress telomerase.</p>
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<p><span style="font-size:14px"><strong> Conclusion</strong></span></p>
<pstyle="margin-left: 40px;"> Telomere and the activity of telomerase can prevent aging, by protect DNA. Also, long telomere can be meant longer life when considering only within one organism. However, longer length of telomere and high activity of telomerase do not necessarily means longer life. As considering their habitat such as sea-life and land-life, their metabolism like homeotherm, and their body size relating with cancer there is a lot of variables in different species. For these reasons, each species might have certain telomere length and the activity of telomerase which are<strong> </strong>optimized to its own situation. In other words, each species has evolved to maintain their longer life or for their own profit considering numerous variables in their own condition.</p>
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