Glycerophospholipid

Sphingomyelin

Another important type of lipid in the cell membrane, the molecule is relatively small, dispersed among phospholipid molecules

It is composed of hydrophilic lipid molecules, lipids and oligosaccharides. Glycolipids are commonly found on the surface of prokaryotic and eukaryotic cell membranes, accounting for less than 5% of the total membrane lipids. More than 40 types of glycolipids have been discovered so far, and their main difference lies in their different polar heads. The simplest glycolipid is cerebroside) which has only one galactose or glucose residue in its polar head group and is the major glycolipid in myelin. In all cells, glycolipids are located in the non-cytoplasmic monolayer of the lipid bilayer, and the sugar groups are exposed on the cell surface.

Lipid bilayer has characteristics as an ideal junction for biological membranes

Also known as penetrating membrane proteins, they account for 70% to 80% of the total membrane proteins and are also amphiphilic molecules. Can be separated with detergent

Also known as peripheral proteins, they account for 20% to 30% of the total membrane proteins. It is a type of protein that is loosely bound to the cell membrane and is not inserted into the lipid bilayer. It is distributed on the cytoplasmic side or extracellular side of the plasma membrane.

Also known as adiponectin. Such membrane proteins can be located on both sides of the membrane, much like peripheral proteins, but differ in that lipid-anchored proteins are covalently bound to lipid molecules within the lipid bilayer. Lipid-anchored proteins covalently bind to lipid molecules in two ways. One is located on the cytoplasmic side of the plasma membrane. Some intracellular signaling proteins directly form covalent bonds with certain fatty acid chains (such as myristic acid, palmitic acid or isoprenyl) in the lipid bilayer and are anchored in the lipid bilayer. double layer

Differences in the distribution of membrane lipid components give intracellular biological membranes different characteristics and functions. Some lipid molecules (such as phosphatidylinositol) in the lipid bilayer can provide binding sites for specific proteins and play an important role in maintaining the correct positioning and polarity of membrane proteins in the lipid bilayer. In addition, the asymmetric distribution of membrane lipids causes different fluidities between the inner and outer layers of the lipid bilayer.

Membrane protein distribution is absolutely asymmetric

The distribution of membrane sugars is significantly asymmetric

Membrane fluidity is one of the basic characteristics of cell membranes and a necessary condition for cells to carry out life activities. The membrane is a dynamic structure, and its fluidity mainly refers to the fluidity of membrane lipids and the mobility of membrane proteins.

As the main body of biological membrane, the lipid bilayer has both the orderly arrangement of solid molecules and the fluidity of liquid. These two characteristics are in a state between the crystalline state and the liquid state, that is, liquid. Quality is an extremely important property of cell membranes. The water environment inside and outside the cell prevents membrane lipid molecules from escaping from the lipid bilayer. At mild temperatures (37°C), membrane lipid molecules can move back and forth, left and right, and exchange positions with each other in the plane of the lipid monolayer. Lipids It exists in a relative flow state, but the long axes of the molecules are basically parallel and the arrangement maintains a certain direction. The film at this time can be regarded as a two-dimensional fluid.

lateral diffusion

flipping motion

rotational motion

bending motion

Degree of saturation of fatty acid chain

Fatty acid chain length

Dual regulatory effects of cholesterol

Lecithin to sphingomyelin ratio

Effect of membrane proteins

other

lateral diffusion

rotational motion

Some non-lipid-soluble (or hydrophilic) substances cannot pass through the cell membrane by simple diffusion, but they can follow the substance concentration gradient or electrochemical gradient mediated by certain carrier proteins without consuming the metabolic energy of the cell. Carry out transport, this method is called facilitated diffusion or helped diffusion. Since facilitated diffusion does not consume cellular metabolism, this is the same as simple diffusion, both of which are passive transport.

structure specificity

saturation phenomenon

competitive inhibition

P-type ion pump, Na＋-K pump, Ga pump, V-type proton pump, F-type proton pump, ABC transporter

Co-transport and counter-transport