Several types of protein molecules with individual functions are found in the membrane structure of living cells. The first of these types are transmembrane proteins, which are molecules with a cylindrical plane; this allows substances to move directly across the membrane according to concentration gradients.
In addition, there are surface membrane proteins attached to one of the two sides of the membrane. Surface proteins often act as receptors to ensure efficient binding to antigens. There are also peripheral proteins associated with ion channels, which are only temporarily attached to the membrane and can be relatively easily removed.