Which of the following statements not true for restriction enzyme which is used in genetic engineering ?

Options

A. It recognizes a palindromic nucleotide sequence
B. It is an endonuclease
C. It is isolated from viruses
D. It produces the same kind of sticky ends in different DNA molecule

Answer

To determine which statement is not true for restriction enzymes used in genetic engineering, we will analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Understanding Restriction Enzymes**:
- Restriction enzymes are proteins that recognize specific short nucleotide sequences in DNA.
- They are crucial in genetic engineering as they cut DNA at specific sites, known as restriction sites or target sequences.

2. **Identifying Characteristics of Restriction Enzymes**:
- They recognize palindromic nucleotide sequences, which means the sequence reads the same forwards and backwards.
- They function as endonucleases, meaning they cut within the DNA strand rather than at the ends.

3. **Source of Restriction Enzymes**:
- Most restriction enzymes are isolated from bacteria, not viruses. This is a key point to remember.

4. **Types of Cuts Made by Restriction Enzymes**:
- Restriction enzymes can produce either sticky ends (overhanging ends) or blunt ends (straight cuts) when they cut DNA.

5. **Evaluating the Statements**:
- **Statement 1**: Restriction enzymes recognize palindromic sequences. (True)
- **Statement 2**: They are endonucleases. (True)
- **Statement 3**: They have been isolated from viruses. (Not True - they are primarily isolated from bacteria)
- **Statement 4**: They produce the same kind of sticky ends in different DNA molecules. (True)

6. **Conclusion**:
- The statement that is not true regarding restriction enzymes is that they have been isolated from viruses. Therefore, the correct answer is **Option 3**.