Chemical knives of DNA are :

Options

A. endonucleases
B. ligases
C. transcriptases
D. polymerases

Answer

To solve the question "Chemical knives of DNA are:", we need to analyze the options provided and understand the functions of each enzyme mentioned.

### Step-by-Step Solution:

1. **Understanding the Term "Chemical Knives":**
- The term "chemical knives" refers to substances that can cut or cleave DNA. This implies that we are looking for an enzyme that has the ability to break the DNA strands.

2. **Analyzing the Options:**
- **Option 1: Endonucleases**
- Endonucleases are enzymes that cut the DNA at specific internal sites. The term "endo" means inside, indicating that these enzymes can cleave the DNA strand within the molecule.

- **Option 2: Ligases**
- Ligases are enzymes that join two DNA fragments together. They do not cut DNA; instead, they facilitate the joining of DNA strands.

- **Option 3: Transcriptases**
- Transcriptases (or RNA polymerases) are enzymes that synthesize RNA from a DNA template. They are involved in transcription, not in cutting DNA.

- **Option 4: Polymerases**
- Polymerases are enzymes that synthesize DNA or RNA. DNA polymerases replicate DNA, while RNA polymerases transcribe RNA. They do not cut DNA.

3. **Identifying the Correct Answer:**
- Based on the definitions and functions of the enzymes, the only enzyme that fits the description of "chemical knives" that cut DNA is **endonucleases**.

4. **Final Answer:**
- Therefore, the answer to the question "Chemical knives of DNA are:" is **endonucleases**.