Sucrose synthase is a plant enzyme that catalyzes the biosynthesis of the disaccharide sucrose from UDP-glucose and β-D-fructofuranose.

(a) Draw the structure of UDP-glucose, assuming it has the same stereochemistry at the anomeric carbon as UDP-galactose.

(b) Draw out the reaction for sucrose biosynthesis. Does this reaction occur with retention or inversion of stereochemistry at the anomeric carbon of UDP-glucose?

(c) Sucrose synthase contains no metal cations in its active site. However, it does contain arginine and lysine residues in their cationic, conjugate-acid form (shown below) near the UDP-glucose binding site. What role are these residues likely to play in the synthase mechanism?

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H₂N protein NH C-N-CH₂CH₂CH₂ H C H protein H₂N structure of an arginine (Arg) residue in a protein protein NH H₂N-CH₂CH₂CH₂CH₂ C H protein structure of a lysine (Lys) residue in a protein