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Contains oligosaccharides with one or more sialic acid moieties (which give gangliosides a net negative charge)-Can protect the membrane against the harsh conditions found there (low pH, high concentrations of degradative enzymes)-Function in cell-recognition processes – in which membrane-bound carbohydrate-binding proteins (lectins) bind to the sugar groups on both glycolipids and glycoproteins in cell-cell adhesion-Can provide entry points for certain bacterial toxins and viruses
Review of BLG 311 Cell Biology31My notes:-Lipid-linked protein-Entirely exposed at the external cell surface, being attached to the lipid bilayer only by a covalent linkage (via a specific oligosaccharide) to a lipid anchor in the outer monolayer of the plasma membrane-Made as soluble proteins in the cytosol and are subsequently anchored to the membrane by the covalent attachment of the lipid group
Review of BLG 311 Cell Biology32My notes – Steps in the folding of a multipass transmembrane protein-When a newly synthesized transmembrane alpha-helix is released into the lipid bilayer it is initially surrounded by lipid molecules-As the protein folds, contacts between the helices displace some of the lipid molecules surrounding the helices
Review of BLG 311 Cell Biology33My notes-In single pass transmembrane proteins the polypeptide chain crosses only once-Oligosaccharide chains and disulfide bonds are all on the noncytosilic side-Sulfhydryl groups in the cytosilic domain do not normally form disulfide bonds because the reducing environment in the cytosol maintain these groups in their reduced (-SH) form-Oligosaccharid chains-About 30% of an organisms proteins are transmembrane proteins-Hydropathy plots cannot identify the membrane-spanning segments of a beta barrel