The latter proteins are often-times ion channels, as their outer layer is hydrophobic and more interactive with the cell membrane, while the center portion is hydrophilic. This hydrophilic region allows ions to traverse the cell membrane to regulate ion balance inside and outside the cell. As a general rule, these compounds are the compounds used for cell recognition or cell identification. Glycolipids are also found in the membrane. They tend to stabilize the structure of the membrane.
Cholesterol is found in cell membranes, as well.
Inside the cell, underneath the cell membrane is a system of microtubules that acts as the cytoskeleton. These microtubules provide a framework to give a shape to the cell. They also act as the cell's irrigation system - more on this, later. Figure 2 illustrates that different glycoproteins provide RBC's with unique identifying markers. Indeed, before the invention of DNA testing, it was by these substances that people were determined to be at the scene of a crime.