科普專欄–薯不揀單 - 深入淺出–無病無痛的話，人類是否會永生？

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？791Please respect copyright.ＰＥＮＡＮＡNMX9lj1pEX
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答案是，不會。791Please respect copyright.ＰＥＮＡＮＡAbkZy5GluJ
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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。791Please respect copyright.ＰＥＮＡＮＡwj2XVIqhOn
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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。791Please respect copyright.ＰＥＮＡＮＡLV4AufvqHq
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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。791Please respect copyright.ＰＥＮＡＮＡ5eVyejgxM3
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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。791Please respect copyright.ＰＥＮＡＮＡgwepRUtd52
然而，當幹細胞變成正常細胞後，Telomerase的功能便會消失。791Please respect copyright.ＰＥＮＡＮＡj38pmzfokm
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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。791Please respect copyright.ＰＥＮＡＮＡgFSDpZUlUJ
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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。791Please respect copyright.ＰＥＮＡＮＡusjaEzc8hq
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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？791Please respect copyright.ＰＥＮＡＮＡNxHtS83M1j
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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。791Please respect copyright.ＰＥＮＡＮＡKrCVC0S1uW
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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。791Please respect copyright.ＰＥＮＡＮＡHqofPNahcx
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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。791Please respect copyright.ＰＥＮＡＮＡJhJW1GpNrL
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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？791Please respect copyright.ＰＥＮＡＮＡbFqleeRmmG
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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。791Please respect copyright.ＰＥＮＡＮＡXK9PzS1pNG
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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；791Please respect copyright.ＰＥＮＡＮＡmhgKk5SPpN
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。791Please respect copyright.ＰＥＮＡＮＡTI6OXsZxiX
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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。791Please respect copyright.ＰＥＮＡＮＡgsAKoRtMZL
而老鼠每年會減少7000單位Telomere長度，最高壽命為5歲。791Please respect copyright.ＰＥＮＡＮＡUXcNRpCBPS
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人類：每年減少71；120歲791Please respect copyright.ＰＥＮＡＮＡaOVA6Q2LDn
大象：每年減少109；66歲791Please respect copyright.ＰＥＮＡＮＡ4pogmaIiWy
紅鸛：每年減少105；60歲791Please respect copyright.ＰＥＮＡＮＡduvEI7YiQX
海豚：每年減少766；52歲791Please respect copyright.ＰＥＮＡＮＡzNKqP14jKa
兀鷲：每年減少209；41歲791Please respect copyright.ＰＥＮＡＮＡ3cyfz3dOkx
海鷗：每年減少771；25歲791Please respect copyright.ＰＥＮＡＮＡr6ayzBE94l
馴鹿：每年減少531；22歲791Please respect copyright.ＰＥＮＡＮＡsqlh9imy9w
山羊：每年減少363；21歲791Please respect copyright.ＰＥＮＡＮＡ6bxqVv8tiB
老鼠：每年減少7000；5歲791Please respect copyright.ＰＥＮＡＮＡkCRf8P599Y
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龜又是每年減少幾多呢？有待有心人發掘。791Please respect copyright.ＰＥＮＡＮＡtweWrMzKmY
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https://www.penana.com/user/27349/%E8%96%AF%E4%BB%94%E8%81%9E%E8%8C%B1%E8%8E%89/portfolio791Please respect copyright.ＰＥＮＡＮＡJkr6rHpx3k
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有興趣接收科學資訊的話，歡迎follow IG: potatopigtongue。791Please respect copyright.ＰＥＮＡＮＡfDJEhXlzA7
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Ref1:https://www.pnas.org/content/116/30/15122791Please respect copyright.ＰＥＮＡＮＡ2NXLthClXo

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