Lipid bilayer facts for kids

Phospholipid

Lipid bilayers are important in biological cells. They are the basis of cell membranes, and they surround most cell organelles. Lipid bilayers form automatically from phospholipids by self-assembly.

The phospholipids have heads which mix with water and tails which reject water. So the tails come together in the centre of the double layer, and the heads on the outside are surrounded by water.

The lipid bilayers stop most water-soluble (hydrophilic) molecules passing through. They also stop most ions.

In cells, proteins are put in the bilayer by enzymes. The proteins decide which molecules come in and which go out of the cell. For example, cells control salt concentrations and pH by pumping ions across their membranes using proteins called ion pumps.

Images for kids

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  This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine.

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  Illustration of a GPCR signaling protein. In response to a molecule such as a hormone binding to the exterior domain (blue) the GPCR changes shape and catalyzes a chemical reaction on the interior domain (red). The gray feature is the surrounding bilayer.

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  Transmission Electron Microscope (TEM) image of a lipid vesicle. The two dark bands around the edge are the two leaflets of the bilayer. Historically, similar images confirmed that the cell membrane is a bilayer

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  Human red blood cells viewed through a fluorescence microscope. The cell membrane has been stained with a fluorescent dye. Scale bar is 20μm.

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  3d-Adapted AFM images showing formation of transmembrane pores (holes) in supported lipid bilayer

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  Illustration of a typical AFM scan of a supported lipid bilayer. The pits are defects in the bilayer, exposing the smooth surface of the substrate underneath.

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  Structure of a potassium ion channel. The alpha helices penetrate the bilayer (boundaries indicated by red and blue lines), opening a hole through which potassium ions can flow

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  Exocytosis of outer membrane vesicles (MV) liberated from inflated periplasmic pockets (p) on surface of human Salmonella 3,10:r:- pathogens docking on plasma membrane of macrophage cells (M) in chicken ileum, for host-pathogen signaling in vivo.

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  Schematic illustration of the process of fusion through stalk formation.

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  Diagram of the action of SNARE proteins docking a vesicle for exocytosis. Complementary versions of the protein on the vesicle and the target membrane bind and wrap around each other, drawing the two bilayers close together in the process.

See also

In Spanish: Bicapa lipídica para niños