If I'm talking about two DNA strands and they differ only in one or two base pairs they won't be exact complements and they won't form this double helix.

假设有两条DNA单链,有一两个碱基不能配对,它们就不能完全互补,也无法形成双螺旋形结构

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Now DNA is a double helix and I've only shown you one part of the helix, right? I've shown you one upright strut and a base hanging off of it, but it forms a double helix because complementary strands of DNA strongly associate with one another and that's a very stable structure.

NA是双螺旋,我只是给你们讲了螺旋的一边,我给你们演示,一条链的支柱及碱基团,但其能构成双螺旋,是因为DNA是完全互补的两条链,彼此之间结合紧密,结构异常稳定

耶鲁公开课 - 生物医学工程探索课程节选