During electrophoresis of the digested DNA , the DNA fragment closest to the cathode is

Options

A. the heaviest and is positively charged
B. the lightest and is positively charged
C. the heaviest and is negatively charged
D. the lightest and is negatively charge

Answer

To solve the question regarding the position of DNA fragments during 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 and charge. When an electric field is applied, DNA fragments migrate through a gel.

**Hint**: Remember that DNA has a negative charge due to its phosphate backbone.

2. **Charge of DNA**:
- DNA is negatively charged. This means that when an electric field is applied, DNA fragments will move towards the positive electrode (anode).

**Hint**: Think about the direction of movement: negatively charged particles move towards positive charges.

3. **Fragment Size and Movement**:
- Smaller DNA fragments can move more easily through the gel matrix, while larger fragments encounter more resistance and move more slowly.

**Hint**: Consider how size affects mobility in a gel; larger fragments will be slower.

4. **Positioning of Fragments**:
- As a result of the differences in size, the smallest fragments will travel the farthest towards the anode, while the largest fragments will remain closer to the starting point, which is near the cathode (negative electrode).

**Hint**: Visualize the gel as a maze; larger fragments get stuck more easily than smaller ones.

5. **Conclusion**:
- Therefore, the DNA fragment closest to the cathode will be the heaviest (largest) fragment, which is still negatively charged.

**Final Answer**: The correct answer is **C**: the heaviest and is negatively charged.