医学细胞生物学 细胞膜Cell Membrane-英文版.ppt

Cell Membrane Variation of biomembranes in different cells The faces of cellular membranes Cytosolic face Exoplasmic face Phospholipid bilayers The phospholipid bilayer, the basic structural unit of all biomembranes, is a two-dimensional lipid sheet with hydrophilic faces and a hydrophobic core, which is impermeable to water-soluble molecules and ions. Properties: Semi-permeable barrier Stable structure maintained by van der Vaals and hydrophobic interaction. Lipid Protein Carbohydrate The primary lipid components of biomembranes are phosphoglycerides, sphingolipids, and steroids. A phospholipid is a lipid that has a positively charged head that is linked by a phosphate group to the fatty acid tails. A glycolipid has a head consisting of an oligosaccharide, linked to a fatty acid tail. A sterol is a compound containing a planar steroid ring. General features of lipids Amphipathic structures have two surfaces, one hydrophilic and one hydrophobic. Lipids are amphipathic. Different cellular membranes vary in lipid composition . Phospholipids and sphingolipids are asymmetrically distributed in the two leaflets of the bilayer, whereas cholesterol is fairly evenly distributed in both leaflets. Asymmetry of lipids Fluidity of Biomembrane Most lipids and many proteins are laterally mobile in biomembranes. Natural biomembranes generally have a fluidlike consistency. In general, membrane fluidity is decreased by sphingolipids and cholesterol and increased by phosphoglycerides. Lipid rafts Lipid rafts are microdomains containing cholesterol, sphingolipids, and certain membrane proteins that form in the plane of the bilayer. These aggregates are sites for signaling across the plasma membrane. Protein Composition On the basis of the nature of the membrane–protein interactions. Integral protein Lipid-anchored protein Peripheral protein Carbohydrates O-link, Ser N-link, Asp Common features of biomembrane Selectively permeable, fluidity and asymmetry. Atomic force micr