Distinguish between endonuclease and exonucleases.

Explanation

### Step-by-Step Solution

1. **Definition**:
- **Endonuclease**: An enzyme that cleaves the phosphodiester bonds within a polynucleotide chain, resulting in the fragmentation of the internal nucleotide sequences.
- **Exonuclease**: An enzyme that cleaves the phosphodiester bonds at the ends of a polynucleotide chain, removing nucleotides one at a time from the terminal ends.

2. **Site of Action**:
- **Endonuclease**: Acts on the internal sites of the nucleotide chain.
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