Properties of biological membranes

The permeability of the membrane (which expresses the rate of passive diffusion of particles through the membrane), is based on the Fick's law of diffusion and depends on several factors:

1. Size and polarity of the permeating molecule – small and non-polar molecules cross the membrane easily, while larger and polar molecules usually need transporters or channels.
2. Concentration gradient – ​​the higher the concentration of a substance on one side of the membrane, the greater the tendency for it to penetrate to the opposite side. This rule also applies to other gradients – such as electrochemical (given by the difference in charges on both sides of the membrane) or osmotic (given by the difference in osmotically active particles on both sides of the membrane).
3. Membrane thickness – the thicker the membrane, the slower substances pass through it.
4. Membrane area – a larger amount of substance can pass through a larger area of ​​the membrane per unit of time.

Other properties of membranes include the degree of thermal and electrical insulation, electrical charge. The overall charge of the cytoplasmic membrane is negative – it is primarily due to negative sialic acid residues in glycolipids and glycoproteins. Membranes have the ability of selective transport.