Restriction endonuclease -

Options

A. Cuts the DNA molecules randomly
B. Cuts the DNA molecules at specific sites
C. Restricts the synthesis of DNA inside the nucleus
D. Synthesizes DNA

Answer

### Step-by-Step Solution:

1. **Understanding Restriction Endonuclease**:
- Restriction endonucleases are enzymes that cut DNA at specific sequences. They are essential tools in biotechnology, especially in recombinant DNA technology.

2. **Types of Cleaving Enzymes**:
- There are two main types of cleaving enzymes:
- **Exonucleases**: These enzymes remove nucleotides from the ends of DNA molecules. They are used to cut DNA segments located at the terminal ends.
- **Endonucleases**: These enzymes cut DNA at specific internal sites, allowing for the removal of DNA segments located in the middle of the molecule.

3. **Specificity of Restriction Endonucleases**:
- Restriction endonucleases are a subset of endonucleases. They are characterized by their ability to recognize and cut DNA at specific sequences, known as restriction sites. Each restriction enzyme has a unique recognition sequence.

4. **Evaluating the Options**:
- The question provides several statements regarding restriction endonucleases. We need to evaluate each option:
- **Option 1**: "Cuts the DNA molecules randomly." - This is incorrect because restriction endonucleases cut DNA at specific sites, not randomly.
- **Option 2**: "Cuts the DNA molecule at a specific site." - This is correct as it aligns with the definition of restriction endonucleases.
- **Option 3**: "Restrict synthesis of DNA." - This is incorrect; restriction endonucleases do not restrict DNA synthesis; they cleave DNA.
- **Option 4**: "Synthesizes DNA." - This is also incorrect as restriction endonucleases are cleaving enzymes, not synthesizing enzymes.

5. **Conclusion**:
- Based on the evaluation, the correct answer is **Option 2**, which states that restriction endonucleases cut the DNA molecule at a specific site.