This blue chain here goes from 5' carbon all along the chain and there's a 3' carbon left open at the bottom.

这条蓝色的链,从5'碳开始一直向下延伸,以3'碳做为链的末端

耶鲁公开课 - 生物医学工程探索课程节选

If I wanted to link another nucleotide to this DNA chain what would I attach here on the bottom?

如果想把另一核苷酸连接到这条DNA链,我将会在DNA链末端添加什么

耶鲁公开课 - 生物医学工程探索课程节选