JEE Main · 2021 · Shift-ImediumBIO-040

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

Biomolecules · Class 12 · JEE Main Previous Year Question

Question

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

Options
  1. a

    C1\text{C}-1 of glucose and C6\text{C}-6 of galactose

  2. b

    C1\text{C}-1 of galactose and C4\text{C}-4 of glucose

  3. c

    C1\text{C}-1 of glucose and C4\text{C}-4 of galactose

  4. d

    C1\text{C}-1 of galactose and C6\text{C}-6 of glucose

Correct Answerb

C1\text{C}-1 of galactose and C4\text{C}-4 of glucose

Detailed Solution

Step 1: Identifying Monosaccharide Linkage Points — Lactose is formed from D-galactose\text{D-galactose} and D-glucose\text{D-glucose} units.

Step 2: Glycosidic Bond Type — The linkage is a β-glycosidic\beta\text{-glycosidic} bond formed between C1\text{C1} of the galactose unit and C4\text{C4} of the glucose unit.

Step 3: Naming the Linkage — This is formally known as a β14\beta 1 \rightarrow 4 glycosidic linkage. Correct option is (b).

Remember: In lactose, the galactose unit is always the non-reducing end, while the glucose unit provides the reducing end.

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