Functional properties of cell membrane

The human body is formed by cell division and differentiation, so it can be said that humans are composed of cells. Human cells are mainly composed of cell membranes and cell nuclei, which also contain vacuoles. The cell membrane is the outermost semipermeable membrane of the cell. It is called a semipermeable membrane because it has an osmotic effect. In addition to this function, what other functional characteristics does the cell membrane have? Let's learn about it below.

Structural characteristics of cell membrane: The cell membrane has a certain fluidity.

The structure of the cell membrane is that the middle phospholipid bilayer constitutes the basic skeleton, and protein molecules are embedded, penetrated, and covered in the phospholipid bilayer or on the surface at different depths. The phospholipid molecules and protein molecules that make up the membrane are mostly mobile, and the movement of substances in and out of cells through the cell membrane is based on the fluidity of the membrane.

Functional characteristics of cell membrane: cell membrane is selectively permeable.

The cell membrane has the function of regulating the entry and exit of substances into and out of the cell. Substances enter and exit the cell through diffusion, osmosis, passive transport, active transport, endocytosis and exocytosis. The types and quantities of carrier proteins on the membrane are different, so many molecules and ions cannot enter and exit the cell at will.

Cell membrane:

Also known as plasma membrane. A thin membrane on the surface of cells. Sometimes called the extracellular membrane or plasma membrane. The thickness is about 7 to 8 nm, and the chemical composition of the cell membrane is basically the same, mainly composed of lipids, proteins and carbohydrates. The content of each component is approximately 50%, 40%, and 2%~10% respectively. Among them, the main components of lipids are phospholipids and cholesterol. In addition, the cell membrane also contains a small amount of water, inorganic salts and metal ions.

Structure of cell membrane:

1. Membrane lipids: Membrane lipids are mainly composed of phospholipids, cholesterol and a small amount of glycolipids. In the membrane lipids of most cells, phospholipids account for more than 70% of the total, cholesterol does not exceed 30%, and glycolipids do not exceed 10%. Phospholipid molecules exist in the plasma membrane in the form of a lipid bilayer, with the hydrophilic ends facing the extracellular fluid or cytoplasm, and the hydrophobic fatty acid hydrocarbon chains facing each other, forming a hydrophobic region inside the membrane.

2. Membrane proteins: Cell membrane proteins (including enzymes) are mainly combined with membrane lipids in two forms: intrinsic proteins and extrinsic proteins. Intrinsic proteins are covalently bound to the hydrophobic part of phospholipids with their hydrophobic parts, and both ends are polar, penetrating the inside and outside of the membrane; extrinsic proteins are bound to the outer ends of intrinsic proteins or to the hydrophilic heads of phospholipid molecules with non-covalent bonds. Such as carriers, specific receptors, enzymes, and surface antigens.

There are two main types of transport proteins on the cell membrane: carrier proteins and channel proteins. Carrier proteins, also known as carriers, permeases and transporters, can bind to specific solutes and transfer the bound solutes to the other side of the membrane through changes in their own conformation. Some carrier proteins require energy to drive, while others do not, and transport substances by assisted diffusion.

3. Membrane sugar: membrane sugar and sugar coating: glycoproteins and glycolipids. Cell membrane carbohydrates are mainly oligosaccharide chains and polysaccharide chains, which are covalently bound to membrane lipids or proteins to form glycolipids and glycoproteins.

Cell membrane functions:

1. Separate and form cells and organelles, provide a relatively stable internal environment for the life activities of cells, greatly increase the area of ​​the membrane, and improve the biological functions occurring on the membrane.

2. Barrier effect: water-soluble substances on both sides of the membrane cannot pass freely.

3. Selective transport of substances, accompanied by the transfer of energy.

4. Biological functions: hormone action, enzymatic reaction, cell recognition, electron transfer, etc.

5. Function of identifying and transmitting information (mainly relying on glycoproteins).

6. Material transport function: The exchange of materials between cells and the surrounding environment is achieved through the transport function of cell membranes.