Nature has been doing these animations for a while now, but they just released one about RNAi - at least I think it’s new; it’s the first I’ve seen of it. If you haven’t heard of RNAi, you should. It’s a technology we’re going to be hearing more and more about in the next few decades. I’ll let the animation explain the rest:
http://www.nature.com/nrg/multimedia/rnai/animation/index.html