Question

Identify the glycosidic linkage present in lactose.

• A. $\alpha - 1, 6$
• B. $\alpha - 1, 4$
• C. $\beta - 1, 4$
• D. $\alpha, \beta - 1, 2$

Hint:

Remember the carbohydrate connection map: $\text{Maltose} \rightarrow \alpha$-1,4 linkage $\text{Lactose} \rightarrow \beta$-1,4 linkage $\text{Sucrose} \rightarrow \alpha$-1, $\beta$-2 linkage A quick mnemonic: Lactose has a "$\beta$"etter connection for milk!

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The problem asks for the specific type of glycosidic linkage that connects the monosaccharide units together to form the disaccharide lactose (commonly known as milk sugar).

Step 2: Detailed Explanation:
Lactose is a disaccharide sugar composed of two distinct monosaccharide subunits: $\beta$-D-galactose and $\beta$-D-glucose. The condensation reaction occurs between the anomeric carbon C1 of the $\beta$-D-galactose molecule and the hydroxyl (-OH) group on the C4 position of the $\beta$-D-glucose molecule. Because the hemiacetal hydroxyl group at C1 of galactose points upwards in the $\beta$ configuration, the resulting oxide bridge holding the two rings together is classified as a $\beta$-1,4-glycosidic linkage. Looking at other options, an $\alpha$-1,4-linkage is found in maltose, $\alpha$-1,6-linkages form the branches in amylopectin, and $\alpha,\beta$-1,2-linkages connect sucrose.

Step 3: Final Answer: The glycosidic bond present inside lactose is a $\beta$-1,4-glycosidic linkage, which corresponds to option (C).