Question

Name and describe the technique that helps in separation and isolation of DNA fragments after cutting of DNA by restriction endonucleases.

Hint:

Technique is agarose gel electrophoresis; DNA moves to the anode by size, is stained with ethidium bromide, and bands are eluted.

Answer 1

Step 1: Name of the technique:
The technique is gel electrophoresis. Agarose is the most commonly used gel matrix.

Step 2: Why the fragments move:
DNA is negatively charged because of its phosphate groups. When an electric field is applied, the fragments move towards the positive electrode (anode).
The gel works like a sieve, so smaller fragments move faster and travel farther than bigger ones.

Step 3: Steps of the method:
1. The cut DNA fragments are loaded into wells at the cathode end of the agarose gel.
2. An electric current is passed through the gel in a buffer.
3. The fragments separate according to their size.
4. The gel is stained with ethidium bromide and seen under UV light. Each fragment shows up as a bright orange band.

Step 4: Isolation of the fragments:
The bands are cut out of the gel. The DNA is then taken out of the gel piece (elution) and purified.
This purified DNA is used for making recombinant DNA.

Final Answer:
Gel electrophoresis separates the cut DNA by size in an agarose gel; bands are stained with ethidium bromide, seen under UV, then cut out and eluted.