Glycerophospholipid

Sphingomyelin

The content is higher in animal cell membranes and less in plants, accounting for about 2% of membrane lipids. It is also an amphipathic molecule, with a sterol ring in the middle and a hydroxyl group connected to the sterol ring as the head.

Function: It plays an important role in regulating the fluidity of the membrane and strengthening the stability of the membrane. The hydrophobic sterol is flat and rigid. It is fixed on the hydrocarbon chain near the head of the phospholipid molecule and interferes with the movement of the tail of the fatty acid chain of the phospholipid.

Properties: It is a hydrophilic lipid molecule, composed of lipids and oligosaccharides

Existence: Commonly found on the surface of prokaryotic and eukaryotic cell membranes, Content accounts for less than 5% of the total

In all cells, glycolipids are located in the non-cytolipid monolayer of the lipid bilayer. Sugar groups are exposed on the cell surface

Function: as a carrier, containing drugs or DNA, and transferring them into cells to study their biological effects Can be prepared with single or mixed phospholipids and can also embed different membrane proteins

Forms a barrier separating two water-soluble environments

The membrane double layer is continuous and has the tendency to fuse with itself to form a closed cavity. No free boundaries were found within the cells, forming an extensive continuous pattern network

Lipid bilayers are flexible and can undergo variability, such as during cell division, movement, budding and fusion of secretory vesicles and fertilization all involve the deformable properties of the membrane.

intrinsic membrane protein

external membrane protein

lipid anchored protein

lipid anchored protein

A~C. Transmembrane proteins, in the form of A helices or B barrels that penetrate the membrane once or multiple times D. Located on the cytoplasmic side, it binds to the membrane by interacting with the lipid monolayer on the cytoplasmic surface through the hydrophobic surface of the a-helix exposed on the protein surface; E. The lipid anchor protein located on the cytoplasmic side directly binds to the fatty acid chain in the lipid monolayer on the cytoplasmic side through covalent bonds; F. Lipid-anchored protein GPI located on the outer surface of the plasma membrane G and H membrane extrinsic proteins indirectly bind to the membrane through non-covalent interactions with the polar heads of membrane lipids or the hydrophilic regions of intrinsic proteins.

The composition and distribution of lipid components in different membranous organelles are different. Allowing organisms within cells to have different properties and functions. Some lipid molecules in the lipid bilayer can provide binding sites for specific proteins. It plays 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 results in different fluidity between the inner and outer layers of the lipid bilayer.

Membrane protein distribution is absolutely asymmetric

The distribution of membrane sugars is significantly asymmetric, and the oligosaccharide side chains of cell membrane glycolipids and glycoproteins are only distributed on the outer surface of the plasma membrane. In the endomembrane system, oligosaccharide side chains are distributed on the inner surface of the membrane cavity.

lateral diffusion

flipping motion

rotational motion

bending motion

Degree of saturation of fatty acid chains: The more unsaturated fatty acids, the lower the relative temperature of the membrane and the greater the fluidity

The length of the fatty acid chain: the fatty acid chain is short, the phase transition temperature is low, and the fluidity is high

Dual regulatory effect of cholesterol: Animal cell membranes contain more cholesterol, which stabilizes the plasma membrane and increases order when the temperature is above the phase transition temperature; Below the phase transition temperature, the sudden decrease in membrane fluidity at low temperatures can be prevented.

Lecithin to sphingomyelin ratio: The ratio of lecithin to sphingomyelin decreases and the fluidity decreases

Influence of membrane proteins: the more embedded proteins, the more interface lipids, and the less fluidity of membrane lipids

Lateral diffusion: membrane proteins can float freely in membrane lipids and diffuse on the surface

Rotational motion: also called rotational diffusion, membrane proteins can rotate around an axis perpendicular to the membrane plane. slow diffusion

mark

1.P-type ion pump: two independent large subunits, with ATP binding sites, and most also have 2 small beta subunits, which usually regulate

V-type proton pump: mainly exists only in the membrane acidic compartment of eukaryotic cells

F-type proton pumps mainly exist in bacterial plasma membranes, mitochondrial inner membranes and chloroplast membranes. It is the energy released by the hydrogen ion concentration gradient operation, which converts ADP into ATP. Occasionally proton transport and ATP synthesis, therefore the F-type proton pump is also called hydrogen ion ATP synthase.

ABC transporter is a type of transport protein that functions as ATP.

Co-transport: It is the joint transport of two solute molecules in the same direction mediated by a carrier protein

Opposite transport: the same transporter transports two different ions or molecules in opposite directions across the membrane, driven by ion concentration gradients

gated type

Ungated

Channel proteins mediate passive transport. The channel is bidirectional. The net flux of ions depends on the electrochemical degree. The channel protein does not bind to solute molecules during the transport process.

Ion channels are highly selective for the size and charge of the transported ions.

Ligand-gated channels: actually ion channel-type receptors that bind to specific extracellular ligands After binding, after the conformation occurs, the "door" is opened, allowing certain ions to quickly diffuse across the membrane.

Voltage-gated channels: Changes in membrane potential are the direct factor that controls the opening and closing of voltage-gated channels.

Stress-activated channel: The channel protein changes its conformation upon sensing stress, opening the channel to open the "gate", and ions entering the cell through the clear water channel, causing changes in membrane potential and generating electrical signals.

selective water channel

water-glycerol channel

Receptors are concentrated in specific areas of the lipid membrane called caveolae (proteins)

clathrin

Uncoated vesicles are formed and fuse with endosomes and lysosomes in sequence

The LDL receptor is composed of a single 839-amino acid Cross-modulating glycoprotein, when cells need to use cholesterol, The cell synthesizes the LDL receptor and embeds it into the plasma membrane.

adapter protein