How does a bacterial cell protect its own DNA from restriction enzymes?

Options

A. By adding methyl groups to adnenies and cystosines
B. By reinforcing bacterial DNA structure with covalent phoshodiester bonds
C. By adding histonest to protect the double-strended DNA
D. By forming "sticky ends" of bacterial DNA to prevent the enzyme from attaching.

Answer

### Step-by-Step Solution:

1. **Understanding Restriction Enzymes**:
- Restriction enzymes are proteins that recognize specific short sequences of nucleotides in DNA and cut the DNA at these specific sites, known as restriction sites or target sequences.

2. **Bacterial Defense Mechanism**:
- Bacteria produce their own restriction enzymes to defend against foreign DNA, such as that from viruses (bacteriophages). However, they need to protect their own DNA from being cut by these enzymes.

3. **Methylation of DNA**:
- To protect their DNA, bacteria modify their own DNA by adding methyl groups (CH3) to specific nucleotides within the recognition sequences of the restriction enzymes. This process is known as DNA methylation.

4. **Recognition of Methylated vs. Unmethylated DNA**:
- The restriction enzymes are unable to cut DNA that has been methylated at the recognition sites. Therefore, when the bacterial DNA is methylated, it is recognized as "self" and is not targeted by the restriction enzymes.

5. **Conclusion**:
- The primary method by which bacterial cells protect their own DNA from restriction enzymes is through the addition of methyl groups to adenine and cytosine nucleotides in the recognition sequences, preventing the enzymes from cutting their own DNA.