Question

Identify the sugar containing $\alpha, \beta$-1,2-glycosidic linkage.

• A. Sucrose
• B. Maltose
• C. Lactose
• D. Raffinose

Hint:

Sucrose is uniquely formed by locking the two reducing/anomeric carbons of its component monomers together (C1 of glucose and C2 of fructose). This head-to-head structural arrangement is why it is the only common non-reducing disaccharide and the only one with a 1,2-linkage.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks us to identify which of the given sugars features a glycosidic bond connecting the $\alpha$ position of one monosaccharide unit to the $\beta$ position of another via a 1,2-linkage.

Step 2: Key Formula or Approach:
Analyze the biochemical composition and specific glycosidic linkages of the listed disaccharides and oligosaccharides to find the match.

Step 3: Detailed Explanation:
1.

Sucrose: It is a disaccharide composed of $\alpha$-D-glucopyranose and $\beta$-D-fructofuranose. The linkage is formed between the anomeric carbon C1 of glucose (in the $\alpha$ configuration) and the anomeric carbon C2 of fructose (in the $\beta$ configuration). Therefore, it contains an $\alpha, \beta$-1,2-glycosidic linkage. Since both anomeric centers are involved in the bond, sucrose is a non-reducing sugar.
2.

Maltose: It is composed of two $\alpha$-D-glucose units linked by an $\alpha$-1,4-glycosidic bond.
3.

Lactose: It is composed of $\beta$-D-galactose and $\beta$-D-glucose units joined together via a $\beta$-1,4-glycosidic bond.
4.

Raffinose: It is a trisaccharide containing a galactose unit linked $\alpha$-1,6 to a sucrose unit, making its individual linkages different from a simple 1,2-linkage between two units.

Step 4: Final Answer:
The sugar containing the $\alpha, \beta$-1,2-glycosidic linkage is sucrose, which corresponds to option (A).