The molecular structure of DNA can be imagined as a zipper with each tooth represented by one of four letters (A,C,G,or T),and with opposite teeth forming one of two pairs,either A-T or G-C.

• DNA的分子结构可以想象成具有每一个牙齿代表A、C、G或T四个字母之一的拉链，对应的牙齿形成两对中的一对，A-T或G－C。