The orientation of some proteins is important, too. Different possibilities to fix integrated membrane proteins within the membrane . The N-terminus is always at the side that is turned away from the cytosol. Membranes have numerous functions. Permeability for one type of molecule and impermeability for another belong to the properties that hint at the presence of a membrane.
All biological membranes are selectively permeable.
Membranes separate reaction areas that can be distinguished due to their chemical composition, their pH value and their electric potential. Both the pH and the electric gradient can be measured . This transport is energy-consuming. It is also spoken of an active transport in contrast to passive transport that occurs only in the direction of the concentration gradient. Due to different compositions have the single membrane types different functions, too.