There are ................ distinct types of restriction enzymes.

Explanation

**Step-by-Step Solution:**

1. **Understanding Restriction Enzymes**:
- Restriction enzymes, also known as restriction endonucleases, are proteins that cut DNA at specific sequences. They are essential tools in molecular biology for DNA manipulation.

2. **Types of Restriction Enzymes**:
- There are three primary types of restriction enzymes:
- **Type 1 Restriction Enzymes**: These enzymes cut DNA at random sites far from their recognition sequences and require ATP for their activity. They are not commonly used in biotechnology.
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