JEE Main 2020 · 8 January · evening · Single correct · +4 / −1
Two monomers in maltose are :
- (a) α-D-glucose and α-D-galactose
- (b) α-D-glucose and α-D-Fructose
- (c) α-D-glucose and α-D-glucose
- (d) α-D-glucose and β-D-glucose
Answer and solution
Answer (c) α-D-glucose and α-D-glucose
Solution
Chemistry ma’am · 3 steps
Maltose comes from breaking down starch, and starch is built only from α-D-glucose, so both halves match.
- Where maltose comes from. The enzyme diastase breaks starch into maltose. Starch is a chain of α-D-glucose units only, so its two-unit piece can contain nothing but α-D-glucose.
- The linkage. C1 of one α-D-glucose joins C4 of the other through an oxygen bridge. This is an α(1→4) glycosidic bond. The second unit keeps a free anomeric carbon, so maltose is a reducing sugar.
Disaccharide Monomer units Linkage Sucrose α-D-glucose + β-D-fructose C1 (glucose) to C2 (fructose) Maltose α-D-glucose + α-D-glucose C1 to C4 Lactose β-D-galactose + β-D-glucose C1 (galactose) to C4 (glucose) - So. Maltose is made of two α-D-glucose units, which is option (c).
The idea to keep. Learn the three disaccharides as a set: sucrose is glucose + fructose, lactose is galactose + glucose, maltose is glucose + glucose, all α.
Answer from the NTA final answer key. Solution by PrepWiser.