You can say a polymer of DNA, for example, is four bases long, that means it has four of these repeat units and they go in the sequence from 5' to 3' of .

打个比方,要描述一个由,四个核苷酸单位构成的寡聚DNA,就是说它由四个核苷酸单位构成,并且从5'端到3'端的顺序为

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