A restriction endonuclease breaks down between
a) Base pairs of a DNA molecule
b) Base pairs of a DNA- RNA
c) Sugar and phosphate components of a nucleic acid molecule
d) Exons & introns of a DNA molecule

Options

A. Base pairs of a DNA molecule
B. Base pairs of a DNA- RNA
C. Sugar and phosphate components of a nucleic acid molecule
D. Exons & introns of a DNA molecule

Answer

To solve the question regarding where a restriction endonuclease breaks down, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Function of Restriction Endonucleases**:
- Restriction endonucleases are enzymes that cut DNA at specific sequences. They are often referred to as "molecular scissors" because they create incisions in the DNA molecule.

2. **Identify the Target of Restriction Endonucleases**:
- These enzymes recognize specific sequences in the DNA, known as restriction sites, which typically contain palindromic sequences.

3. **Determine the Location of the Cut**:
- The cuts made by restriction endonucleases occur at the sugar-phosphate backbone of the DNA. This means they cleave the bonds between the sugar and phosphate components of the nucleic acid molecule, rather than between the base pairs or within the bases themselves.

4. **Evaluate the Options**:
- a) Base pairs of a DNA molecule: This option is incorrect because the enzyme does not cut between the base pairs.
- b) Base pairs of a DNA-RNA: This option is also incorrect for the same reason as option a.
- c) Sugar and phosphate components of a nucleic acid molecule: This option is correct as it accurately describes where the restriction endonuclease acts.
- d) Exons & introns of a DNA molecule: This option is incorrect because restriction endonucleases do not specifically target exons and introns.

5. **Conclusion**:
- The correct answer is **c) Sugar and phosphate components of a nucleic acid molecule**.