Proteins that are part of or connected to biological membranes are called membrane proteins. The plasma membrane that encloses cells, the membranes of organelles within cells, and the membranes of viruses are all examples of specialised membrane-bound structures found in living creatures.
Many biological processes rely on membrane proteins, such as molecule and ion transport, cell adhesion, and cell-to-cell communication. A common way to describe membranes is in terms of their hydrophobic and hydrophilic portions; the former are found within the membrane, while the latter are exposed to the aqueous environment on either side.
Structure and membrane interactions are used to categorise membrane proteins. Peripheral membrane proteins are connected with the membrane but can be removed without affecting the membrane, while integral membrane proteins are embedded within the membrane and can only be removed by disrupting the membrane. Lipid-anchored proteins are proteins that are linked to the membrane by a lipid molecule, while transmembrane proteins cover the entire width of the membrane.