然而，干细胞里四分之一的甲基胞核嘧啶却没有鸟嘌呤随后。
A quarter of the methylated cytosines in stem cells, however, were not followed by guanines.
葡萄糖和肝糖原的胞内作用在四个地方被严格控制。
The intracellular use of glucose and glycogen is tightly regulated at four points.
它们可以附在胞核嘧啶上，胞核嘧啶是组成基因代码的“字母”的四种碱基数之一，帮助调控转录的过程。
These can attach themselves to cytosine , one of the four chemical bases that form the "letters" of the genetic code.
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