Carbohydrates碳水化合物【清华大学出品】.ppt

Selectin-mediated movement of immune cells The role of lectin-ligand interaction in lymphocyte (neutrophil) movement to the site of infection or injury. Helicobacter pylori cells adhering to the gastric surface. This bacterium causes ulcers by interaction between lectin and the Leb oligosaccharide of the gastric epithelium. Bacteria lectin-mediated gastric ulcer formation Roles of oligosaccharides in recognition and adhesion at the cell surface Some key points we have learned Lectins, protein with highly specific carbohydrate-binding domains, are commonly found on the outer surface of cells, where they initiate interaction with other cells. Proteoglycan are macromolecules of the cell surface or extracellular matrix in which one or more glycosaminoglycan chains are joined covalently to a membrane protein or a secreted protein. Glycoproteins are carbohydrate-protein conjugates in which carbo- hydrate moieties are smaller and more diverse than the glycosamino- glycans of proteoglycan. Glycolipids and lipopolysaccharides are the lipids that have oligo- accharides covalently bound to them. They are usually found on the outer face of the plasma membrane. Reducing vs nonreducing sugars Sucrose Reducing sugar Non-reducing sugar Maltose Fehling’s test The production of a red precipitate of Cu2O is a classic sugar test—Fehling’s test that was used to test of excess sugar in blood and urine of diabetics. Some key points we have learned Sugars are compounds containing an aldehyde or ketone group and two or more hydroxyl groups. Monosaccharides generally contain several chiral carbons, therefore exist in a variety of stereochemical forms. In aqueous solution, monosaccharides (C5) exist predo- minantly in cyclic form with either α or ? configuration. Oligosaccharides are short polymers of several mono- saccharides joined by glycosidic bonds. Sugars are reducing agents if contain an anomeric carbon at one end of the chain. Polysaccharides (Glycan)