Which of the following enzymes cut off nucleotides from 5' or 3' ends of DNA molecules?

Options

A. Endonucleases
B. Exonucleases
C. Restriction endonucleases
D. Alkaline phosphatases

Answer

To solve the question "Which of the following enzymes cut off nucleotides from 5' or 3' ends of DNA molecules?", we can follow these steps:

### Step-by-Step Solution

1. **Understand the Question**: The question asks for enzymes that cut nucleotides specifically from the 5' or 3' ends of DNA molecules. This indicates that we are looking for enzymes that can remove nucleotides from the ends of DNA.

2. **Identify Types of Enzymes**: There are two main types of enzymes that interact with DNA ends:
- **Exonucleases**: These enzymes remove nucleotides from the ends of DNA molecules, either from the 5' end or the 3' end.
- **Endonucleases**: These enzymes cut DNA at specific internal sites, not at the ends.

3. **Focus on Exonucleases**: Since the question specifies cutting from the 5' or 3' ends, we should focus on exonucleases. Exonucleases can remove nucleotides one at a time from either end of the DNA strand.

4. **Conclusion**: Based on the understanding that exonucleases are responsible for cutting nucleotides from the ends of DNA, the correct answer to the question is that **exonucleases** cut off nucleotides from the 5' or 3' ends of DNA molecules.

### Final Answer
The enzymes that cut off nucleotides from the 5' or 3' ends of DNA molecules are **exonucleases**.

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