Chemical knives of DNA are :

Options

A. endonuclease
B. Polymerase
C. ligase
D. transcriptase

Answer

To answer the question "Chemical knives of DNA are:", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The term "chemical knives" refers to enzymes that can cut DNA. We need to identify which of the given options serves this function.

2. **Identifying the Options**: The options provided are:
- Endonucleases
- Polymerases
- Ligases
- Transcriptases

3. **Analyzing Each Option**:
- **Endonucleases**: These are enzymes that cut DNA at specific internal sites. They are indeed referred to as "chemical knives" because they cleave the phosphodiester bonds within the DNA strand.
- **Polymerases**: These enzymes are responsible for adding nucleotides to a growing DNA strand during replication. They do not cut DNA, so they do not fit the description of "chemical knives."
- **Ligases**: These enzymes join two DNA fragments together. They act like glue but do not cut DNA, so they are not "chemical knives."
- **Transcriptases**: These enzymes synthesize complementary DNA from RNA (cDNA) but do not cut DNA. Therefore, they do not fit the definition of "chemical knives."

4. **Conclusion**: Based on the analysis, the correct answer is **Endonucleases**, as they are the enzymes that cut DNA at specific sites.

### Final Answer:
Chemical knives of DNA are **Endonucleases**.

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