Irradiated mammalian cells usually stop dividing and arrest at a G 1 / S checkpoint. Place the following events in the order in which they should occur. 1. cell cycle arrest 2. DNA damage 3. inhibition of cyclin-Cdk complexes 3 , 2 , 1 2 , 3 , 1 3 , 1 , 2 2 , 1 , 3.