RNA, the single-stranded precursor to DNA, normally expands one nucleic base at a time, growing sequentially like a linked chain.

DNA的单链前体分子，一般一次延伸一个碱基，就像延长的锁链。

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Carbohydrates are made of simple sugars, proteins are made up of 20 amino acids, and nucleic acids are compose of oxy - and deoxy - nucleic sugars and 5 base pairs.

其中碳水化合物都是由单糖构成的，蛋白质是由20种氨基酸构成的，核酸是由核糖、脱氧核糖、和5种碱基构成。

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