How many restriction endonuclease enzymes have been isolated till date from various bacteria?

Options

A. 200
B. 900
C. 1500
D. 1900

Answer

To determine how many restriction endonuclease enzymes have been isolated from various bacteria, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Restriction Endonucleases**:
- These are enzymes that cut DNA at specific sites, known as restriction sites. They are crucial in molecular biology for DNA manipulation.

2. **Review the Options**:
- We have four options to consider:
- A) 200
- B) 900
- C) 1500
- D) 1900

3. **Evaluate Each Option**:
- **Option A (200)**: This is incorrect as it underestimates the number of known enzymes.
- **Option B (900)**: This is the correct answer, as it is reported that 900 restriction enzymes have been isolated from 230 strains of bacteria.
- **Option C (1500)**: This is incorrect; it overestimates the number of enzymes.
- **Option D (1900)**: This is also incorrect; it further overestimates the number of enzymes.

4. **Conclusion**:
- After evaluating the options, the correct answer is **900** restriction endonuclease enzymes have been isolated from various bacteria.

### Final Answer:
The correct option is **B) 900**.

---