胶纯化是用来在琼脂糖凝胶中回收电泳分离的DNA片段的标准步骤。将胶溶解后，让它通过一种特殊的滤膜，这一步骤使得DNA与其他杂质，如盐，游离核苷酸，酶等分离开，从而可以进行下游的应用操作。
胶纯化的基本原理
从琼脂糖凝胶中回收DNA的基本原理涉及到一系列的结合，清洗和洗脱步骤。当胶完全溶解在溶解缓冲液中后，上样到一个“离心柱”上，它通过离心可使DNA分子特异性的结合到硅胶膜上，而其他的杂质则通过柱子到了收集管。
由于凝胶溶解缓冲液中的高盐浓度，使得DNA可以结合到硅胶上。该缓冲液会破坏膜周围的水合结构，在强阴性的膜和阴性的DNA之间建立一个阳离子盐桥。剩余的杂质则被乙醇清洗去掉。
水或低盐缓冲液加到柱子上，被认为会打断阳离子盐桥而将DNA洗脱下来。这样DNA就从胶中被纯化出来。
胶纯化步骤
胶纯化步骤中的第一步是要制备琼脂糖凝胶和对DNA样品跑电泳。跑胶完成后，在紫外灯下观察DNA片段并通过与分子量标准样进行比较来选择要回收的片段。
如果凝胶未被染色，可通过DNA标准样来大致判断带的位置。当用刀片切割胶时，要一定小心用尽可能小体积的凝胶回收到尽可能多的DNA样品。
使用溴化乙锭染色凝胶和在紫外灯前操作时，必须要带上手套和防护眼镜。将目的DNA从凝胶中切割出来后，要依据实验室安全条例步骤正确地处理凝胶和跑胶溶液。
将切割下来的胶条放在一个微量离心管中并在电子称上称重。100毫克的胶重被大致算作100微升体积，将4倍于胶重体积的溶解缓冲液加入含胶条的小管。然后放置在50度孵育来熔化胶。
胶熔化后，将它们加入到离心柱上，离心去掉溶液，这样所有的DNA和其他的颗粒都附着到了滤膜上。
接下来，在滤膜上加入70%乙醇并离心来清洗结合的DNA，去除滤膜上残余的杂质。弃去洗脱物，重复该清洗步骤三次。再将空的滤膜离心一次来去除所有剩余的乙醇，将硅胶滤膜放室温下晾干。最后，加入水或洗脱缓冲液到滤膜并离心，纯化的DNA就被收集到了管子的底部。
您刚看到的是使用硅胶滤膜离心管来进行胶纯化。还有其他的方法也同样用到了DNA先与硅胶结合，然后进行清洗和洗脱的原理。例如，DNA可与被称之为玻璃奶的硅胶悬液混合，然后将其离心下来，清洗，再进行洗脱。此外，也可以使用抽真空的方式来让DNA通过硅胶膜，然后洗脱。一定要了解您所在实验室用到的胶回收流程。
应用
现在，您已经学习了如何从琼脂糖凝胶中回收DNA。让我们再来看看对这些胶回收的DNA的下游的一些应用。
例如，胶纯化可以是染色质免疫沉淀中的一个中间步骤，该技术是用来分离与基因组DNA结合的调节蛋白，从而可以判断哪些序列受到调控。将分离得到的片段进行胶纯化并进行测序，这样可将它们定位到各自的染色体区域。
亚克隆, 是一种将基因从一个载体转移到另一个载体的过程, 其中也会用到胶纯化。例如，一个载体上的基因序列会酶切下来，然后通过PCR嵌合上其他序列，再被胶纯化并插入到其他载体上。
胶纯化最简单的应用也许用它来回收-80度长期保存的电泳后切割下来的DNA。
结语
您现在已经了解了如何从琼脂凝胶中回收DNA片段，根据不同要求来改动结合，清洗和洗脱流程，以及该方法下游的一些应用。我们一如既往地感谢您的观看。
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