Q.20 Disaccharide molecules that contain β(1 → 4) glycosidic linkage are
- (A) sucrose and maltose
- (B) sucrose and isomaltose
- (C) maltose and isomaltose
- (D) lactose and cellobiose
Answer: (D) lactose and cellobiose
Disaccharides with β(1→4) glycosidic linkages include lactose and cellobiose, as both feature this specific bond between monosaccharide units.
Option Analysis
Sucrose: Sucrose consists of α-D-glucose and β-D-fructose linked by an α(1→2) glycosidic bond, lacking any β(1→4) linkage.
Maltose: Maltose forms from two α-D-glucose units connected via an α(1→4) glycosidic bond, not β.
Isomaltose: Isomaltose links two α-D-glucose molecules through an α(1→6) glycosidic bond.
Lactose: Lactose joins β-D-galactose to D-glucose with a β(1→4) glycosidic bond.
Cellobiose: Cellobiose connects two β-D-glucose units via a β(1→4) glycosidic bond, mimicking cellulose’s repeating unit.
Disaccharides containing β(1→4) glycosidic linkage, such as lactose and cellobiose, play key roles in biology and nutrition. This β(1→4) glycosidic linkage differs from α linkages by its configuration at the anomeric carbon, affecting digestibility and structure.
Key Disaccharides Breakdown
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Lactose: Primary sugar in milk, β-D-galactopyranosyl-(1→4)-D-glucose; hydrolyzed by lactase.
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Cellobiose: β-D-glucopyranosyl-(1→4)-D-glucose; structural unit of cellulose, indigestible by humans.
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Common errors exclude α-linked maltose (α(1→4)) and sucrose (α(1→2)).
Exam Relevance
In questions like “Disaccharide molecules that contain β(1→4) glycosidic linkage are,” option (D) lactose and cellobiose is correct, distinguishing from α forms in maltose and isomaltose.
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