that they receive from outside the cell and

它们能将外界获得的信息
transmit them through the membrane into the cells internal apparatus,

通过细胞膜传递给细胞器
and that's what they do.

这正是它们的功能
The signal comes in the form of molecules

信号通常以分子的形式来传递
which we're going to call throughout the lecture here 'ligands'.

在这门课里我们把这种分子叫做配体
This terminology 'ligand' and 'receptor' you've probably heard before.

你们可能听过配体和受体这两个术语
It refers to usually 'receptors'

受体这个词通常代表了
that are fixed in a cell, on a cell membrane,

固定于细胞表面的分子
and 'ligands' which are dispersed throughout the body

而配体分散于体内各处
and free to diffuse around,

能够自由扩散
and occasionally will find the cell.

它们偶尔会与细胞邂逅
When they do find the cell

但当它们遇到细胞时