JEE Main · 2020 · 06 Sep 2020 · Shift 2 · Biomolecules

Which one of the following statements is not true?

(A)Lactose contains an $α$ -glycosidic linkage between $C_{1}$ of galactose and $C_{4}$ of glucose.✓ Correct
(B)Lactose is a reducing sugar and it gives Fehling's test.
(C)Lactose ( $C_{12} H_{22} O_{11}$ ) is a disaccharide and it contains 8 hydroxyl groups.
(D)Lactose on hydrolysis gives one molecule of $D (+)$ -glucose and one molecule of $D (+)$ -galactose.

Answer: (A)

Solution

Lactose is 4-

O

β

-D-galactopyranosyl)-D-glucose, so the glycosidic bond joining

C_{1}

of galactose to

C_{4}

of glucose is a

β

-linkage, not an

α

-linkage; the statement describing it as

α

-glycosidic is therefore the one that is not true. The remaining statements are correct: the glucose unit keeps a free anomeric hydroxyl, so lactose is a reducing sugar and answers Fehling's test; its molecular formula is

C_{12} H_{22} O_{11}

with eight free hydroxyl groups; and on hydrolysis it gives one molecule each of

D (+)

-glucose and

D (+)

-galactose.

Structure Structure of Lactose — Structure of Lactose

JEE Main · 2020 · 06 Sep 2020 · Shift 2 · Single correct option

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JEE Main · 2020 · 06 Sep 2020 · Shift 2 · Biomolecules

Solution

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