無病無痛，沒有任何交通或人為意外的話，人類是否會進入不死永生狀態呢？709Please respect copyright.ＰＥＮＡＮＡ9URxDyWx5H
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答案是，不會。709Please respect copyright.ＰＥＮＡＮＡFNHIbuf26E
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箇中的原因，就是在於染色體亦即是DNA的運作機制之上。709Please respect copyright.ＰＥＮＡＮＡOHSPGKgZqW
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（圖1）正常人體細胞分裂的時候，染色體的長度會越來越短。709Please respect copyright.ＰＥＮＡＮＡZaEBCys0nL
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（圖2）染色體的頂端區域，我們稱之為Telomere。正常細胞分裂後，Telomere的長度便會越來越短，所以導致染色體的總長度亦會有所減少。709Please respect copyright.ＰＥＮＡＮＡKiKzz63lXN
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（圖3）而幹細胞進行分裂的時候，則會有著Telomerase的協助，導致Telomere的長度便並不會有所減少。709Please respect copyright.ＰＥＮＡＮＡFXGBhOeERV
然而，當幹細胞變成正常細胞後，Telomerase的功能便會消失。709Please respect copyright.ＰＥＮＡＮＡOhoyGbZBJN
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（圖4）當Telomere長度削減到一定程度的時候，細胞便會自行啟動機制滅亡，又或者陷入衰老(Senescence)狀態。709Please respect copyright.ＰＥＮＡＮＡm9ubhlXDV1
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細胞滅亡或衰老的話，器官的功能便會衰退，最後亦會支撐不住，無法正常運作，促成死亡。709Please respect copyright.ＰＥＮＡＮＡGabwWylYOA
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你可能會問，現在科技如此倡明，那麼我們只要學習幹細胞的那一套方式，動用外力重啟Telomerase功能，那不就能踏入永生嗎？709Please respect copyright.ＰＥＮＡＮＡuYKc6sh3Pn
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這個思路並沒有錯，只不過代價就是會增加患癌的風險。709Please respect copyright.ＰＥＮＡＮＡ0fru8sOTPn
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事實上，不少癌細胞的特徵就是Telomere長度非常之短，但又有著一定水平的Telomerase功能穩定維持著Telomere的長度，逃避進入滅亡的命運。709Please respect copyright.ＰＥＮＡＮＡWjUiiJo5FG
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另一方面的想，如果細胞真的是踏入「永生」狀態的話，終有一天無可避免會累積各種的DNA變異，促成癌細胞的誕生。709Please respect copyright.ＰＥＮＡＮＡJ0SFaZ9NTH
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（圖5）既然Telomere對細胞的壽命有著重要影響的話，那麼一些較為長壽的物種是否擁有較長的Telomere呢？709Please respect copyright.ＰＥＮＡＮＡZ16s6YAvdI
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科學家比較各物種的Telomere後（Ref1)，發現海豚的起始Telomere長度比人類高出6倍以上，但壽命長度始終是人類佔優。709Please respect copyright.ＰＥＮＡＮＡTfh5ZZapR7
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反而，決定物種壽命長度的其中一種因素，則是Telomere衰減的速度；709Please respect copyright.ＰＥＮＡＮＡhehjhFwQv4
Telomere衰減的速度只是一個參考性的指標，並非絕對。物種的大小、新陳代謝機制的不同等等均會對壽命長度有著影響。709Please respect copyright.ＰＥＮＡＮＡeG6VbcCBCD
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人類每年約會減少71單位Telomere的長度，最高壽命為120歲。709Please respect copyright.ＰＥＮＡＮＡNdW1wv3wwd
而老鼠每年會減少7000單位Telomere長度，最高壽命為5歲。709Please respect copyright.ＰＥＮＡＮＡRQFShtolxX
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人類：每年減少71；120歲709Please respect copyright.ＰＥＮＡＮＡbcK9FZh8YV
大象：每年減少109；66歲709Please respect copyright.ＰＥＮＡＮＡO6c4UVwXor
紅鸛：每年減少105；60歲709Please respect copyright.ＰＥＮＡＮＡPQtIF2ycm5
海豚：每年減少766；52歲709Please respect copyright.ＰＥＮＡＮＡIFenq6XKiW
兀鷲：每年減少209；41歲709Please respect copyright.ＰＥＮＡＮＡMaSgaFnuGa
海鷗：每年減少771；25歲709Please respect copyright.ＰＥＮＡＮＡ4Z9W74TSLY
馴鹿：每年減少531；22歲709Please respect copyright.ＰＥＮＡＮＡ5X1ePwHgc4
山羊：每年減少363；21歲709Please respect copyright.ＰＥＮＡＮＡoZIVMXWPdJ
老鼠：每年減少7000；5歲709Please respect copyright.ＰＥＮＡＮＡscgre6LCXa
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龜又是每年減少幾多呢？有待有心人發掘。709Please respect copyright.ＰＥＮＡＮＡxvuyPmi0h8
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如果想我快啲出文的話，請入去Penana網站科普專欄–薯不揀單俾一個like以及Bookmark，這對我非常之重要。709Please respect copyright.ＰＥＮＡＮＡfSUHLC5Hx5
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Link: https://www.penana.com/story/66244/%E7%A7%91%E6%99%AE%E5%B0%88%E6%AC%84-%E8%96%AF%E4%B8%8D%E6%8F%80%E5%96%AE/toc709Please respect copyright.ＰＥＮＡＮＡFyEjEB2Egy
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同時亦可以在Penana網站裡按「買一嚿/半嚿薯仔」，以課金的方式推動我繼續搜羅資料寫文，多謝。709Please respect copyright.ＰＥＮＡＮＡCldCXu5mKj
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Link:709Please respect copyright.ＰＥＮＡＮＡXjI7RFuSCw
https://www.penana.com/user/27349/%E8%96%AF%E4%BB%94%E8%81%9E%E8%8C%B1%E8%8E%89/portfolio709Please respect copyright.ＰＥＮＡＮＡFUTXRfmzC5
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有興趣接收科學資訊的話，歡迎follow IG: potatopigtongue。709Please respect copyright.ＰＥＮＡＮＡa9HN3ZXIvZ
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Ref1:https://www.pnas.org/content/116/30/15122709Please respect copyright.ＰＥＮＡＮＡJgi3nIubXL
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