Restriction endonucleases are called so as they

Options

A. Synthesize DNA
B. Restrict nuclear activity
C. Cleave DNA into fragments
D. Break DNA at random.

Answer

### Step-by-Step Solution:

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases are enzymes that play a crucial role in molecular biology. They are responsible for cutting DNA at specific sequences.

2. **Function of Restriction Endonucleases**:
- These enzymes recognize specific sequences within the DNA, known as restriction sites, and cleave the DNA at or near these sites. This process is essential for various applications in biotechnology, including cloning and DNA manipulation.

3. **Analyzing the Options**:
- **Option A: Synthesized DNA** - This is incorrect because restriction endonucleases do not synthesize DNA; they cut it.
- **Option B: Restrict nuclear activity** - This is also incorrect as these enzymes do not have a role in restricting nuclear activity.
- **Option C: Cleave DNA into fragments** - This is correct because the primary function of restriction endonucleases is to cleave DNA at specific sites.
- **Option D: Break DNA at random** - This is incorrect because restriction endonucleases do not break DNA randomly; they act on specific sequences.

4. **Conclusion**:
- Based on the analysis, the correct answer is that restriction endonucleases are called so because they "cleave DNA into fragments."

### Final Answer:
Restriction endonucleases are called so as they cleave DNA into fragments.

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