It's actually just a bubble sitting on the edge of a much, MUCH larger molecular cloud, hundreds of light years across.

它实际上只是一个气泡，坐落在一个更大的分子云的边缘，分子云直径有几百光年。

In this case, this large molecular machine is looking for a segment of DNA that tells it it's at the beginning of a gene.

在这个例子中，这个大型分子机器在寻找一段能告诉它“这里是基因的起始位置” 的 DNA。