When DNA molecule is cut by the same restriction enzyme, the resultant DNA fragments have the same kind of 'sticky-ends' and these can be joined together (end to end) using

Options

A. E.coli
B. DNA ligase
C. DNA polymerases
D. restriction enzymes

Answer

To solve the question regarding how to join DNA fragments that have been cut by the same restriction enzyme, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Restriction Enzymes**:
- Restriction enzymes are proteins that cut DNA at specific sequences. When a DNA molecule is cut by the same restriction enzyme, it produces fragments with complementary 'sticky ends'.

2. **Identifying Sticky Ends**:
- Sticky ends are short, single-stranded overhangs at the ends of the DNA fragments. These ends can base-pair with each other, allowing the fragments to align properly.

3. **Joining DNA Fragments**:
- To join these sticky ends together, we need an enzyme that facilitates the formation of phosphodiester bonds between the nucleotides of the DNA strands.

4. **Choosing the Correct Enzyme**:
- Among the options provided:
- **E. coli**: This is a type of bacteria, not an enzyme.
- **DNA ligase**: This enzyme is responsible for joining DNA fragments by catalyzing the formation of covalent bonds between the sugar and phosphate groups of adjacent nucleotides.
- **DNA polymerase**: This enzyme synthesizes new DNA strands but does not join fragments.
- **Restriction enzyme**: This enzyme cuts DNA but does not join it.

5. **Conclusion**:
- The correct enzyme to join the sticky ends of the DNA fragments is **DNA ligase**.

### Final Answer:
The resultant DNA fragments can be joined together using **DNA ligase**.

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