Lactose is composed of

Options

A. glucose + glucose
B. glucose + fructose
C. fructose + galactose
D. glucose + galactose

Explanation

To determine what lactose is composed of, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Type of Sugar**:
- Lactose is classified as a disaccharide. Disaccharides are sugars formed by the combination of two monosaccharide units.

2. **Identify the Monosaccharide Components**:
- Lactose is specifically composed of two monosaccharides: glucose and galactose.

3. **Understand the Linkage**:
- The two monosaccharides (glucose and galactose) are linked together by a specific type of bond known as a beta 1,4 linkage. This means that the first carbon of one sugar is linked to the fourth carbon of the other sugar.

4. **Recognize the Source of Lactose**:
- Lactose is commonly known as milk sugar, as it is found in significant amounts in milk.

5. **Enzymatic Breakdown**:
- Lactose can be broken down into its monosaccharide components (glucose and galactose) by the enzyme beta-galactosidase.

6. **Conclusion**:
- Therefore, the correct answer to what lactose is composed of is one molecule of glucose and one molecule of galactose.

### Final Answer:
Lactose is composed of glucose and galactose.

---