A cell membrane is mainly composed of phospholipids and proteins, which are two types of bioorganic molecules. Within the membrane, phospholipids are able to move laterally. Depending on temperature and fatty acid composition, phospholipids generally move faster than proteins.

The proteins slowly drift and bob in the fluid body of phospholipids, much like icebergs floating in an ocean. Proteins are able to change shape (also known as conformation); peripheral proteins are not embedded in the lipid bilayer, but are appendages loosely bound to the membrane surface. For example, carrier proteins are able to bind to specific molecules such as glucose in order to provide transportation for the molecule; once glucose is attached to the carrier protein, the protein changes shape and ferries the glucose inside of the cell.