The backbone's on the outside of the molecule like the upright struts of a ladder on the outside of a ladder.

主链位于DNA分子结构外侧,像梯子两侧上下的支柱,记住是梯子外侧

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The corresponding half of the ladder that corresponds to any given ladder, let's say the black DNA molecule that corresponds to the blue one is not just a mirror image.

与任何单链配对的,另一条单链,比方说与蓝色DNA分子,配对的黑色DNA分子,并不是蓝色DNA分子的镜像

耶鲁公开课 - 生物医学工程探索课程节选

Every unit in the backbone of this ladder has the same sugar unit, the same pentose; it's either RNA or DNA and has ribose or deoxyribose, so you don't need to describe the whole thing.

主链的每个单位,都由相同的糖单位构成,同样的戊糖,RNA里是核糖,DNA里是脱氧核糖,所以你不需要所有细节都描述

耶鲁公开课 - 生物医学工程探索课程节选