Restriction endonuclease cuts

Options

A. ds-DNA
B. ss-DNA
C. single strand of ds-DNA
D. both (2) and (3)

Answer

### Step-by-Step Solution:

1. **Understanding Nucleases**:
- Nucleases are enzymes that cut nucleic acids (DNA or RNA). They are classified into two main types: exonucleases and endonucleases.

2. **Exonucleases vs. Endonucleases**:
- **Exonucleases**: These enzymes remove nucleotides one at a time from the ends of a DNA strand. They can only cut at the terminal ends of the DNA.
- **Endonucleases**: In contrast, endonucleases can cut within the DNA strand itself, meaning they can cleave the DNA at specific internal sites rather than just at the ends.

3. **Restriction Endonucleases**:
- Restriction endonucleases are a specific type of endonuclease. They are known for their ability to recognize and cut double-stranded DNA at specific sequences known as palindromic sequences.

4. **Palindromic Sequences**:
- A palindromic sequence is a sequence of DNA that reads the same forwards and backwards on complementary strands. Restriction endonucleases will only cut at these specific sites.

5. **Conclusion**:
- Therefore, restriction endonucleases specifically cut double-stranded DNA at defined locations, which are palindromic sequences.

### Final Answer:
Restriction endonucleases cut double-stranded DNA at specific palindromic sequences.

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