The biosynthesis of oligosaccharides employs the chemical constituents of proteins and nucleic acids as well as carbohydrates. In the example shown, a disaccharide linkage is created between a molecule of galactose and a molecule of N-acetylgalactosamine. The galactose (the “donor” sugar) is carried into the process as a uridine diphospate ester, and the “acceptor” galactosamine is held in place by a glycoside linkage to the hydroxyl group of a serine residue in a protein. The enzyme galactosyl transferase specifi cally forms a disaccharide linkage between C1 of the donor and C3 of the acceptor: 

What type of basic mechanistic process does this reaction resemble? Discuss the roles played by the various participants of the reaction.

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CH,OH 6 6CH,OH OH H OH H N. H H H. C=0 4 4 OH OH H H H 0-P-0-P-0 о + H О-СН, — СH Serine 3 3 H. H NH H ОН H NH H C=0 ÓH CH3 Uridine diphosphate-galactose N-Acetylgalactosamine-protein