A restriction endonuclease breaks bonds between the

Options

A. base pairs of a DNA molecule
B. base pairs of a `DNA-RNA` hybrid molecule
C. sugar and phosphate components of a nucleic acid molecule
D. exons and introns of a DNA molecule.

Answer

### Step-by-Step Solution:

1. **Understanding Restriction Endonucleases**:
- Restriction endonucleases, also known as restriction enzymes, are proteins that recognize specific sequences of nucleotides in DNA and cleave the DNA at or near these sites.

2. **Evaluating the Options**:
- The question provides four options regarding what bonds restriction endonucleases break. We need to analyze each option.

3. **Option 1: Base pairs of DNA molecule**:
- Base pairs are formed between nucleobases through hydrogen bonds. Restriction endonucleases do not break these hydrogen bonds; they act on the DNA backbone. Therefore, this option is incorrect.

4. **Option 2: Base pairs of DNA-RNA hybrid molecule**:
- Similar to option 1, DNA-RNA hybrids also involve hydrogen bonds between nucleobases. Restriction endonucleases do not cleave these bonds. Thus, this option is also incorrect.

5. **Option 3: Sugar and phosphate components of nucleic acid molecule**:
- Restriction endonucleases cleave the phosphodiester bonds in the sugar-phosphate backbone of DNA. This is the correct function of restriction endonucleases, making this option correct.

6. **Option 4: Exons and introns of DNA molecule**:
- Exons and introns refer to coding and non-coding regions of DNA, respectively. Restriction endonucleases do not specifically break bonds between exons and introns. Therefore, this option is incorrect.

7. **Conclusion**:
- The correct answer is option 3, as restriction endonucleases break the sugar and phosphate backbone of the DNA molecule by hydrolyzing the phosphodiester bonds.

### Final Answer:
The restriction endonuclease breaks bonds between the sugar and phosphate components of nucleic acid molecules (Option 3).

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