Remember that this molecule, let's look at the blue one wouldn't be the same if I turned it upside down.

让我们记住,如果我把蓝色的,单链倒过来,那么这条链和原来不一样了

耶鲁公开课 - 生物医学工程探索课程节选

One is that there are two backbones right here in the light blue, so this would be the upright parts of the ladder that are twisted.

其一是浅蓝色所代表的两条主链,这是构成,扭曲梯子的垂直部分

耶鲁公开课 - 生物医学工程探索课程节选