Bacteria possessing restriction endonucleases remain

Options

A. Affected by bacteriophages
B. Resistant to bacteriophages
C. Resistant to drugs
D. Resistant to heat

Answer

### Step-by-Step Solution:

1. **Understanding the Concept of Restriction Endonucleases**:
- Restriction endonucleases are enzymes produced by bacteria that can cut DNA at specific sequences. They play a crucial role in the bacterial defense mechanism against invading viral DNA (bacteriophages).

2. **Restriction Modification System**:
- Bacteria possess a system known as the Restriction Modification System. This system consists of two main components: restriction enzymes and modification enzymes. The restriction enzymes cut foreign DNA, while the modification enzymes protect the bacteria's own DNA.

3. **Mechanism of Action**:
- When a bacteriophage injects its DNA into a bacterial cell, the restriction endonucleases recognize the foreign DNA and cleave it. This prevents the bacteriophage from replicating within the bacterial cell.

4. **Modification of Bacterial DNA**:
- To protect its own DNA from being cut by its restriction enzymes, the bacteria add methyl groups to specific sites on their DNA. This methylation serves as a marker, allowing the restriction enzymes to differentiate between the bacterial DNA and the foreign viral DNA.

5. **Outcome of the Mechanism**:
- As a result of this mechanism, bacteria that possess restriction endonucleases can effectively restrict the replication of viral DNA while safeguarding their own genetic material. This makes them resistant to the attack of bacteriophages.

### Final Statement:
Bacteria possessing restriction endonucleases remain resistant to the attack of bacteriophages due to their ability to differentiate their own DNA from foreign viral DNA through methylation, allowing them to cut only the viral DNA while protecting their own.

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