How many fragments will be generated on the digestion of a closed circular DNA molecule with a restriction enzyme having six recongnition sites on the DNA ?

Options

A. 5
B. 7
C. 6
D. 9

Explanation

To determine how many fragments will be generated when a closed circular DNA molecule is digested with a restriction enzyme that has six recognition sites, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Circular DNA**:
- A closed circular DNA molecule is a looped structure with no free ends.

2. **Identify the Role of Restriction Enzymes**:
- Restriction enzymes recognize specific sequences of DNA (recognition sites) and cut the DNA at those sites.

3. **Count the Recognition Sites**:
- In this case, the restriction enzyme has six recognition sites on the circular DNA.

4. **Determine the Number of Cuts**:
- Each recognition site will result in a cut in the DNA. Since there are six recognition sites, the enzyme will make six cuts.

5. **Calculate the Number of Fragments**:
- When a circular DNA is cut at multiple sites, the number of fragments produced is equal to the number of cuts made. However, for circular DNA, the number of fragments is equal to the number of cuts made plus one.
- Therefore, if there are 6 cuts, the number of fragments will be 6 (cuts) + 1 = 7 fragments.

6. **Conclusion**:
- The total number of fragments generated from the digestion of the closed circular DNA molecule with the restriction enzyme is 7.

### Final Answer:
The answer is 7 fragments.