How is this asymmetric nature of the membrane actually retained? How is it preserved over time? So what exactly prevents, for instance, these two proteins from actually oring themselves and flipping to the other side? Well, basically, when we discussed flip flopping, or also known as transverse diffusion, we said that proteins cannot actually rotate from one leaflet to the other leaflet, and that's because when they rotate, that is energetically unfavorable, because the proteins contain extensive hydrophilic. So polar regions, when they rotate, that means the polar regions must interact with the hydrophobic core of the membrane. And that is too energetically unfavorable.