The mean free path is pretty much 0 all over, so to speak. I was just trying to tie it back into more EE concepts for you. The idea is that things are just randomly moving about, with a 'free' mean free path, until they aren't, and that stoppage costs energy. At body temperatures, it doesn't take much to knock binding ligands out of a cleft. So the stiffer the bind, the harder to disassociate, and the harder to get it to unbind at the end. Nature kinda figures this all out on her own, and the optimal energies are found out via evolution. It's all a 'good enough' system.
So, the trick with bio is that it's a lot like how Clausewitz thinks of war: War is easy, it's just that all the easy stuff is really hard. In that, it's conceptually easy to do bio. It's just that it's really hard to implement anything. Feynman talked a bit about it in one of his lectures. In that, getting a rat to randomly go into a room and then discover that there is cheese in it will take a tremendous amount of prep and careful cleaning and the like. Rats have really really good noses. It's so easy to fool yourself in bio, because the systems are just so complicated. And, for me, that's been true up and down the size scale, from single cells to whole animals. The systems are just so complex, you really only get to ask simple questions and then hope you controlled the experiment correctly.