The four main functions of the plasma membrane include identification, communication, regulation of solute exchange through the membrane, and isolation of the cytoplasm from the external environment. The plasma membrane is a semi-permeable phospholipid bilayer that contains a hydrophilic head and a non-polar hydrophobic tail. It contains hydrogen bonds between the phospholipids that help hold the plasma membrane together; cholesterol molecules are also embedded into the membrane for fluidity.
The plasma membrane contains channel, carrier, receptor, enzymatic and cell recognition proteins that all contribute to the membrane’s functions. The channel proteins form small openings where certain molecules and solutes diffuse through and get into the cell. Carrier proteins have binding sites that grab onto certain solutes outside of the cell and transport them into the cell. Receptor proteins trigger a set of cellular responses when they are bound.
An example of a cellular response triggered by receptor proteins is the release of hormones. Cell recognition proteins tag immune cells for recognition and help to identify various self cells of the human body. Enzymatic proteins help carry out and regulate metabolic processes that occur within the cell. The plasma membrane protects the cytoplasm and all of the cellular organelles by forming a selective barrier between the cell’s organelles and the outside environment.