The structure of the plasma membrane
Cytoplasmic membrane has a thickness of 8-12 nm, so it is impossible to consider it in a light microscope. The structure of the membrane is studied using an electron microscope.
The plasmic membrane is formed by two layers of lipids — the bilipid layer, or bilayer. Each lipid molecule consists of a hydrophilic head and a hydrophobic tail, with in biological membranes lipids arranged heads outwards, tails inwards.
Numerous protein molecules are immersed in the bilipid layer. Some of them are on the surface of the membrane (external or internal), others permeate the membrane through.
Plasmatic Membrane Functions
Membrane protects the contents of the cell from damage, maintains the shape of the cell, selectively passes the necessary substances inside the cell and exits metabolism products, and also provides cell communication between each other. The
barrier, delineating function of the membrane is provided by a double layer of lipids. It does not allow the contents of the cell to fuse, mix with the environment or intercellular fluid, and prevents the penetration of dangerous substances into the cell.
A number of the most important functions of the cytoplasmic membrane are carried out at the expense of submerged proteins. Using receptor proteins, the cell can perceive various irritations to its surface. Transport proteins form the thinnest channels through which potassium, calcium, sodium and other small diameter ions pass inside and out of the cell. Protein enzymes provide vital processes in the cell itself.
Large food particles unable to pass through thin membrane channels enter the cell by phagocytosis or pinocytosis. The common name for these processes is endocytosis.
As endocytosis occurs — the penetration of large food particles into the cell
The food particle contacts the outer membrane of the cell, and in this place a peel is formed. Then the particle surrounded by the membrane enters the cell, a digestive vacuole is formed, and digestive enzymes penetrate the resulting vesicle.
Blood leukocytes capable of capturing and digesting foreign bacteria are called phagocytes.
In the case of pinocytosis, the membrane is captured not particulate matter, but liquid droplets with dissolved substances. This mechanism is one of the main pathways for substances to enter the cell.
Plant cells covered on top of the membrane by a solid layer of cell wall are incapable of phagocytosis.
The process reverse endocytosis is exocytosis. The substances synthesized in the cell (for example, hormones) are packed into membrane vesicles, fit to the membrane, embedded in it, and the contents of the bubble are thrown out of the cell. Thus, the cell can get rid of unnecessary products of exchange.