Plasma membrane proteins perform a variety of functions: they act preferentially on transport mechanisms, organizing true tunnels that allow substances to pass into and out of the cell, function as membrane receptors, and receive signals from substances that carry some message to the cell, favor adhesion of adjacent cells in a tissue, serve as anchor point for the cytoskeleton.
- Adhesion Proteins: in adjacent cells, membrane proteins may adhere to each other.
- Proteins that facilitate the substance transport between cells.
- Recognition Proteins: Certain glycoproteins act on the membrane as a true "marker seal" and are specifically identified by other cells.
- Membrane receptor proteins.
- Transport Proteins: they can play a role in facilitated diffusion by forming a channel through which some substances pass, or in active transport where energy is supplied by the ATP substance. ATP (adenosine triphosphate) is a nucleotide-derived molecule that stores the energy released in the bioenergetic processes that take place in cells (aerobic respiration, for example). Whenever energy is required to perform cellular activity (active transport, for example) it is supplied by ATP molecules.
- Enzymatic action proteins: One or more proteins may act alone as an enzyme in the membrane or together as if they were part of a “assembly line” of a given metabolic pathway.
- Proteins with anchoring function to the cytoskeleton.