Restriction enzymes are used in genetic engineering be- cause they :

Options

A. can join DNA fragments
B. cut DNA at specific base sequence
C. cut DNA at variable sites
D. are proteolytic enzymes which degrade harmful pro- teins

Answer

**Step-by-Step Solution:**

1. **Understanding Restriction Enzymes**: Restriction enzymes, also known as restriction endonucleases, are proteins that can cut DNA at specific sequences. They are essential tools in genetic engineering.

2. **Functionality of Restriction Enzymes**: These enzymes act like molecular scissors, meaning they can precisely cut DNA molecules at designated locations. This cutting occurs at specific base sequences, which are recognized by the enzyme.

3. **Recognition Sequence**: Each restriction enzyme recognizes a specific sequence of nucleotides (typically 4-8 base pairs long) in the DNA. This sequence is known as the recognition sequence.

4. **Role in Genetic Engineering**: In genetic engineering, the ability to cut DNA at specific sites allows scientists to manipulate genetic material. This includes inserting, deleting, or modifying genes.

5. **Elimination of Incorrect Options**:
- **Joining DNA Fragments**: This is not the role of restriction enzymes; ligase enzymes are responsible for joining DNA fragments.
- **Cutting at Variable Sites**: Restriction enzymes do not cut at random or variable sites; they are specific to their recognition sequences.
- **Proteolytic Enzymes**: These enzymes degrade proteins, not DNA, and are not involved in the function of restriction enzymes.

6. **Conclusion**: The correct reason why restriction enzymes are used in genetic engineering is that they cut DNA at specific base sequences.

**Final Answer**: Restriction enzymes are used in genetic engineering because they cut DNA at specific base sequences.

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