Types of Proteins in Cell Membranes

Cells are surrounded by a membrane called a plasma or cell membrane. The membrane consists of phospholipids and proteins. Phospholipids make up the membrane and create the barrier between the cell's contents and area outside the cell. Two types of proteins are found in the cell membrane: integral and peripheral proteins. According to The Cell: Down to Basics, marker proteins, transport proteins and receptor proteins are the three types of integral proteins.

Receptor Proteins

• A receptor protein is one type of integral, or intrinsic, protein and extends through the cell membrane. The receptor protein receives messages when molecules bind to the part of the protein outside of the cell. When this happens, it triggers a reaction within the cell. Receptor proteins give the cell the ability to communicate with other cells and react to the environment around it.

Marker Proteins

• Marker proteins are intrinsic proteins that identify the cell. They identify the type of cell to other cells and also to the body's immune system. Marker proteins prevent the immune system from destroying its own cells.

Transport Proteins

• Transport proteins, the final type of integral protein, extend through the membrane and transport materials in and out of the cell. Some transport proteins actively move materials in and out of the cell, while other simply provide an opening for materials to passively move.

Peripheral Proteins

• Peripheral proteins, also called extrinsic proteins, do not enter the phospholipid membrane. They attach to the outside of the membrane or to one of the integral proteins. Peripheral proteins help to regulate enzymes and maintain the structure of integral proteins.