<p><span style="font-size:24px"><u><strong>Ageing</strong></u></span></p>
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<p><span style="font-size:20px"><strong>What is the meaning of ageing?</strong></span></p>
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<p><span style="font-size:14px">The process of becoming older. It is a measurement of change dependent to time. Ageing is resulted from combinational process of physical, psychological, and especially biological change. As organism ages the risk of occurring disease increases. There are several diseases whose occurrence correlates with ageing such as Alzheimer's disease, vascular disease, Parkinson's disease and Lou Gehrig's disease. The causes of ageing are unknown. Currently, researchers hypothesize that it is related with the accumulation of environmental damages (external) or to the programmed ageing of cells (internal).</span></p>
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<p><span style="font-size:20px"><strong>Why organisms are aged over time?</strong></span></p>
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<p><span style="font-size:14px">Genetic damage, including mutations of DNA and epimutations which is mutation of regulatory scaffold of gene expression, causes abnormal gene expression and can lead to diseases. Also, accumulation of waste products in cells interferes normal metabolism. The waste accumulates in the cells as small granule which increase size over time. In addition, wear-and-tear theory that changes are resulted from accumulation of random chance of being damaged over time.</span></p>
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<p><span style="font-size:20px"><strong>What can be the criteria for measuring age?</strong></span></p>
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<p><span style="font-size:14px">Telomere is a region at each end of a chromosome with repetitive nucleotide sequences, which protects the end of the chromosome from loss or from fusion with neighboring chromosomes. Shortening of telomeres in cell division can result in cellular senescence. When telomeres become too short, the cells stop to divide then senesce or die. Therefore, the length of telomeres can be used as the molecular clock. The rate of shortening can be either increased or decreased by internal or external factors.</span></p>
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<p><strong><span style="font-size:20px">References</span></strong></p>
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<ol>
<li><span style="font-size:14px"><a href="https://en.wikipedia.org/wiki/Ageing#Biological_basis_of_ageing">https://en.wikipedia.org/wiki/Ageing#Biological_basis_of_ageing</a></span></li>
<li><span style="font-size:14px"><a href="https://en.wikipedia.org/wiki/Telomere">https://en.wikipedia.org/wiki/Telomere</a></span></li>
<li><span style="font-size:14px">Masood, A. S. (2012). Telomeres, lifestyle, cancer, and aging. <em>Curr Opin Clin Nutr Metab Care</em>. <em>14</em>(1): 28–34.</span></li>
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