When the ligand is present it binds to the receptor outside the cell and it activates this G-protein.

当配体存在并与细胞表面的受体结合时,就会激活G蛋白

耶鲁公开课 - 生物医学工程探索课程节选

It gets produced in response to a signal so there's a binding of a ligand to a receptor, the enzyme that does this conversion is activated and more cycle AMP is released.

这类分子的产生是对信号做出的一种反应,当配体和受体结合时,催化这种转化过程的酶被激活,更多的cAMP释放出来

耶鲁公开课 - 生物医学工程探索课程节选