How to make different "enemies" line up

Hello everyone!

I’m making a part of my game a DNA matching game.

I want the single strand of DNA to slide down the screen and I will shoot the each base (ACTG) with it’s pair.

My problem is how do I make the DNA show random base while it slides down the screen.

If I don’t make sense, here is a reference hahahah: https://youtube.com/shorts/Lp4S62aArGs?si=z6HPXCJcf2rNwKd8

It would be nice if someone could help or guide me. Thank you.