Restriction endonucleases are most widely used in recombinant DNA technology. They are obtained from

Options

A. bacteriophage
B. bacterial cells
C. plasmids
D. all prokaryotic cells

Answer

### Step-by-Step Solution:

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases, also known as restriction enzymes, are proteins that can cut DNA at specific sequences. They play a crucial role in recombinant DNA technology by allowing scientists to cut and manipulate DNA.

2. **Historical Context**:
- The discovery of restriction enzymes dates back to 1963, when two enzymes were identified that could restrict the growth of bacteriophages (viruses that infect bacteria) in *E. coli*.

3. **Mechanism of Action**:
- One of these enzymes added a methyl group to the DNA, which is a modification that can protect the bacterial DNA from being cut by the other enzyme. The second enzyme is the one that actually cuts the DNA, which is what we refer to as restriction endonucleases.

4. **Source of Restriction Endonucleases**:
- These enzymes are derived from bacteria, particularly from the *E. coli* species. They function within bacterial cells to protect the bacteria from invading bacteriophages by cutting foreign DNA.

5. **Conclusion**:
- Therefore, the answer to the question is that restriction endonucleases are obtained from bacterial cells, specifically from *E. coli*.

### Final Answer:
Restriction endonucleases are obtained from bacterial cells, specifically from *E. coli*.

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