That means they don't actually span the entire membrane, as shown here. In either case, these integral proteins are attached permanently via these strong hydrophobic nonpolar interactions. And so what that means is, by changing the PH or adding some type of salt, for instance, sodium chloride, these integral proteins cannot actually dissociate from the membrane. But in the case of peripheral proteins, which only interact via these polar regions, by changing the PH or by adding some type of salt solution, we actually disrupt those bonds and that can cause a dissociation of that particular protein. So, two major types of proteins. Now, we'll focus on this in much more detail in a future lecture.