Protein Components

The other main component of a cell membrane is protein.

Proteins can be intrinsic or extrinsic. Intrinsic proteins span the membrane from one side to the other. Extrinsic proteins are found in one side of the bilayer or on the surface of the bilayer. Some intrinsic proteins form channels through the membrane as shown in the diagram.

Proteins have hydrophilic and hydrophobic portions depending on the location of the R group in the primary sequence. Hydrophilic parts with polar/charged R groups are located around the phospholipid heads or on the outside. Hydrophobic portions with non-polar R groups are arranged near/between the hydrophobic tails. Channel proteins often have charged/polar R groups lining the channel.