A piece of DNA is subjected to restriction enzyme digestion and the digested sample is electrophoresed. Which statement is correct in the above context?

Options

A. Smallest fragment is present near cathode
B. Largest fragment is present near anode
C. Largest fragment is present in the middle of the gel
D. Smallest fragment is present near anode

Answer

To solve the question regarding the correct statement about DNA digestion and electrophoresis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Electrophoresis**:
- Electrophoresis is a technique used to separate DNA fragments based on their size. It involves applying an electric field to a gel matrix where the DNA samples are loaded.

2. **Identifying the Electrodes**:
- In electrophoresis, there are two electrodes: the **cathode** (negative end) and the **anode** (positive end). DNA is negatively charged due to its phosphate backbone and will migrate towards the anode when the electric current is applied.

3. **Migration of DNA Fragments**:
- When DNA fragments are subjected to an electric field, smaller fragments move faster and travel further through the gel compared to larger fragments. This is because smaller fragments encounter less resistance in the gel matrix.

4. **Positioning of DNA Fragments**:
- As a result of the migration, the largest DNA fragments will remain closer to the starting point (near the cathode), while the smallest fragments will migrate further towards the anode.

5. **Evaluating the Statements**:
- The statements provided can be evaluated based on the understanding of DNA migration:
- **Statement 1**: The smallest fragment is present near the cathode. (Incorrect)
- **Statement 2**: The largest fragment is present near the anode. (Incorrect)
- **Statement 3**: The largest fragment is present in the middle of the gel. (Incorrect)
- **Statement 4**: The smallest fragment is present near the anode. (Correct)

6. **Conclusion**:
- Based on the analysis, the correct statement is that the smallest fragment is present near the anode.

### Final Answer:
The correct statement is: **The smallest fragment is present near the anode.**

---