And what that means is if we take a look at the membrane so we have two sides of the membrane, two leaflets, one leaflet and the posing leaflet. So the individual fossil lipid molecules, these lipid molecules along any leaflet can move relatively quickly and easily along that leaflet and they move at a rate of about one micro meter per second. Now, proteins within the membrane can also move along that membrane in a lateral direction. Now, some proteins move relatively quickly while other proteins are essentially immobile. Why? Well, because some proteins, like this one here isn't actually physically attached onto any other molecule or any other structure.