Read the following statements for restriction enzymes and choose option which have only correct ones.
A. Restriction enzymes belongs to a large class of enzymes called nuclease.
B. Restriction enzymes are of two kinds: exonuclease and endonuclease.
( C) Restriction enzymes are so called because these only identify particular nucleotide sequence.
( D) In nature appoximately 900 restriction enzymes are present.

Options

A. A, B and D
B. A and B only
C. A, C and D
D. A and D only

Answer

To solve the question regarding the statements about restriction enzymes, we will analyze each statement one by one and determine their correctness.

### Step-by-Step Solution:

1. **Statement A: "Restriction enzymes belong to a large class of enzymes called nuclease."**
- **Analysis:** This statement is correct. Restriction enzymes are indeed a type of nuclease, which are enzymes that cut nucleic acids (DNA or RNA).

2. **Statement B: "Restriction enzymes are of two kinds: exonuclease and endonuclease."**
- **Analysis:** This statement is also correct. Restriction enzymes can be classified into two categories: exonucleases, which remove nucleotides from the ends of DNA, and endonucleases, which cut the DNA at specific internal sites.

3. **Statement C: "Restriction enzymes are so called because these only identify particular nucleotide sequence."**
- **Analysis:** This statement is incorrect. While restriction enzymes do recognize specific nucleotide sequences, they are named "restriction" enzymes because they restrict the growth of bacteriophages by cutting the DNA at specific sites. The focus is on their function rather than just their ability to identify sequences.

4. **Statement D: "In nature approximately 900 restriction enzymes are present."**
- **Analysis:** This statement is also incorrect. While it is true that many restriction enzymes exist, recent discoveries have identified over 3600 different restriction enzymes, with more than 900 being commercially used. Thus, the statement underestimates the actual number of restriction enzymes.

### Conclusion:
The correct statements are A and B. Therefore, the option that contains only the correct statements is the one that includes A and B.