推荐回答（1个）
引物（primer），又名引子。是一小段单链DNA或RNA，作为DNA复制的起始点，在核酸合成反应时，作为每个多核苷酸链进行延伸的出发点而起作用的多核苷酸链，在引物的三′-OH上，核苷酸以二酯链形式进行合成，因此引物的三′-OH，必须是游离的。之所以需要引物是因为在DNA合成中DNA聚合酶仅仅可以把新的核苷酸加到已有的DNA链上。引物是人工合成的两段寡核苷酸序列，一个引物与目的基因一端的一条DNA模板链互补，另一个引物与目的基因另一端的另一条DNA模板链互补。 在PCR（聚合酶链式反应）技术中，已知一段目的基因的核苷酸序列，根据这一序列合成引物，利用PCR扩增技术，目的基因DNA受热变性后解链为单链，引物与单链相应互补序列结合，然后在DNA聚合酶作用下进行延伸，如此重复循环，延伸后得到的产物同样可以和引物结合。PCR引物设计的目的是找到一对合适的核苷酸片段，使其能有效地扩增模板DNA序列。如前述，引物的优劣直接关系到PCR的特异性与成功与否。对引物的设计不可能有一种包罗万象的规则确保PCR的成功，但遵循某些原则，则有助于引物的设计。引物设计有 三 条基本原则： 一、首先引物与模板的序列要紧密互补， 二、其次引物与引物之间避免形成稳定的二聚体或发夹结构， 三、再次引物不能在模板的非目的位点引发DNA聚合反应(即错配)。 具体实现这 三 条基本原则需要考虑到诸多因素，如引物长度，产物长度，序列 Tm 值 ，引物与模板形成双链的内部稳定性，形成引物二聚体及发夹结构的能值，在错配位点的引发效率，引物及产物的GC 含量，等等。必要时还需对引物进行修饰，如增加限制性内切酶位点，引进突变等
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