Protein function includes spanning the plasma membrane to form channels, allowing for the passage of molecules and ions in and out of the cell.
Depending on their location, membrane proteins may be involved with cell-to-cell signaling and interactions, and channeling of molecules and ions into and out of the cell. The transport of molecules and ions through the plasma membrane is done by passive and facilitated diffusion. Finally, membrane proteins located in the "face" of the membrane closer to the cytosol provide anchoring of the cytoskeletal proteins to the membrane for cell structure stability.
