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

Options

A. C-1 of galactose and C-4 of glucose
B. C-1 of glucose and C-6 of galactose
C. C-1 of glucose and C-4 of galactose
D. C-1 of galactose and C-6 of glucose

Answer

To determine the glycosidic linkage present in lactose, which is composed of galactose and glucose, we can follow these steps:

### Step 1: Understand the Composition of Lactose
Lactose is a disaccharide made up of two monosaccharides: galactose and glucose.

### Step 2: Identify the Type of Linkage
The linkage between the two monosaccharides in lactose is a glycosidic bond. We need to specify the type of glycosidic linkage.

### Step 3: Determine the Specific Carbons Involved
In lactose, the glycosidic bond is formed between:
- The anomeric carbon (C1) of galactose
- The C4 carbon of glucose

### Step 4: Identify the Configuration of the Linkage
The glycosidic linkage in lactose is specifically a **beta** linkage because the hydroxyl group (-OH) on the anomeric carbon of galactose is in the same direction as the -OH group on C4 of glucose.

### Step 5: Write the Final Answer
Thus, the glycosidic linkage present in lactose is a **beta-1,4-glycosidic linkage**.

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