Which cleaves DNA at specific sites producing stickly ends

Options

A. Clearing enzyme
B. Proteases
C. Lyases
D. Restriction endonuclease

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which enzyme cleaves DNA at specific sites to produce "sticky ends."

2. **Analyzing the Options**: The options provided are:
- Clearing enzymes
- Proteases
- Lyases
- Restriction endonucleases

3. **Evaluating Each Option**:
- **Clearing Enzymes**: These are not specifically known for cleaving DNA. They do not fit the requirement.
- **Proteases**: These enzymes break down proteins into amino acids. Since the question is about DNA, proteases are not relevant.
- **Lyases**: These enzymes catalyze reactions without hydrolysis. They do not cleave DNA specifically, so they are also not the correct choice.
- **Restriction Endonucleases**: These enzymes specifically cleave DNA at designated sites. They cut the DNA internally (hence the term "endonuclease") and produce sticky ends.

4. **Defining Sticky Ends**: When restriction endonucleases cut DNA, they create ends that are not blunt but have overhanging nucleotides. These overhangs are referred to as "sticky ends" because they can easily bind to complementary DNA sequences, facilitating the insertion of new DNA.

5. **Conclusion**: The correct answer to the question is **restriction endonucleases**, as they cleave DNA at specific sites and produce sticky ends.

### Final Answer:
**Restriction endonucleases cleave DNA at specific sites producing sticky ends.**

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