And proteins cannot diffuse altogether because of that high energy barrier that must be overcome. The polar region, the extensive polar region of the protein cannot interact in a favorable way with the hydrophobic core of that lipid bilayer membrane. Now, in fact, inside our membranes, we have these special proteins known as flipases that actually allow the movement of these phospholipids across that membrane. So lipases are proteins that can assist in the transverse diffusion of lipids. And we'll discuss these in much more detail in future lectures. And so number three proteins do not actually flip flop.