Some proteins can be switched from an 'off' position where they don't do anything to an 'on' position where they now do something by only a chemical reaction like this where a phosphorous is added.

一些蛋白质可以从关闭状态的,无所作为,到成为开启状态后,执行某种功能,中间只发生了一个引入磷酸基的化学反应

耶鲁公开课 - 生物医学工程探索课程节选