The plasma membrane, or cell membrane, consists of a lipid bilayer which separates the interior of the cell from the exterior. The membrane is composed of phospholipids, cholesterol, glycolipids, and a large fraction of membrane proteins, organized together in different domains. The proteins can be subdivided into transmembrane proteins, lipid anchored proteins and peripheral membrane proteins, depending on how they are associated with the plasma membrane. The membrane proteins include channels and transporters, adhesion molecules, receptors, and enzymes, thus providing different biological functions to the plasma membrane. The plasma membrane plays important roles in cell communication and signalling, cell adhesion, cell shape, and cell motility. The plasma membrane is semi-permeable, allowing some small ions and molecules to pass by passive diffusion, but controlling the movement of larger molecules through transmembrane protein channels and transporters.
Immunofluorescent staining of the plasma membrane can give various staining patterns. Sometimes, it appears as a more or less distinct edge around the cell, occasionally with characteristic protrusions or ruffles. In other cases, the staining can be uniform across the entire cell, making it difficult to distinguish between a staining of the plasma membrane and a cytoplasmic staining.
Read more about the proteome of the plasma membrane.