The idea is neat, you have to plan the timing to kill everything, the problem is the control is very unintuitive, because I would assume I can hover my mouse above or under the nucleotide to control it, but the way your game works is hover in the whole area where the arrow is, so when my mouse is on the upper screen the nucleotide always go up, this makes the control really confusing, and stopping them is difficult too

Game was fun! For future projects a way to quit the game might be nice though. Very nice for your first time learning Unity! I hope you keep up your game dev :).