Question

Given below are two statements:
Statement (I): Lactose is a disaccharide composed of D -glucose and D -galactose.
Statement (II): The aldehyde group of galactose is linked to the C-2 group of glucose through a $\beta$ -1, 2-glycosidic linkage.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Lactose is composed of D-galactose and D-glucose joined by a \(\beta\)-1,4-glycosidic linkage.
Because the C-1 of the glucose unit is free, lactose is a reducing sugar.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Lactose is the primary carbohydrate found in the milk of mammals.
It is a disaccharide formed by a condensation reaction between two monosaccharide sugars.

Step 2: Detailed Explanation:
Let us analyze both statements to evaluate their scientific accuracy:
- Statement (I): Lactose is composed of one molecule of D-galactose and one molecule of D-glucose.
Therefore, it is a disaccharide sugar, making Statement (I) correct.
- Statement (II): In the lactose molecule, the linkage is formed between the hemiacetal carbon (C-1) of the \(\beta\)-D-galactopyranose and the hydroxyl group at the C-4 position of the D-glucopyranose molecule.
This is known as a \(\beta\)-1,4-glycosidic linkage (not a \(\beta\)-1,2-glycosidic linkage).
The free aldehyde group on the C-1 of the glucose residue remains unlinked, allowing lactose to act as a reducing sugar.
Therefore, Statement (II) is incorrect.
Since Statement (I) is correct and Statement (II) is incorrect, option (C) is the correct choice.

Step 3: Final Answer:
Statement (I) is correct but Statement (II) is incorrect.