JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Biomolecules

Which of the glycosidic linkage between galactose and glucose is present in lactose?

(A) $C$ -1 of glucose and $C$ -4 of galactose
(B) $C$ -1 of glucose and $C$ -6 of galactose
(C)C-1 of galactose and C-6 of glucose
(D)C-1 of galactose and C-4 of glucose✓ Correct

Answer: (D)

Solution

Lactose is built from one galactose unit and one glucose unit. The anomeric carbon of galactose, C-1, is bound through oxygen to the C-4 hydroxyl of glucose, a

β

-1,4 linkage, which leaves the anomeric carbon of the glucose unit free to open to its aldehyde form, and that is why lactose is a reducing sugar. The linkage joins C-1 of galactose to C-4 of glucose.

JEE Main · 2021 · 25 Feb 2021 · Shift 1 · Single correct option

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