Question

Explain gel-electrophoresis.

Hint:

Smaller DNA fragments travel farther through the gel towards the anode.

Answer 1

Step 1: Principle:
Gel electrophoresis is a technique used to separate DNA, RNA or protein fragments according to their size, using an electric field. Because the phosphate backbone of nucleic acids is negatively charged, DNA/RNA fragments move towards the positive electrode (anode) when placed in an electric field.

Step 2: Procedure:
The sample (a mixture of DNA fragments) is loaded into wells cast in an agarose gel submerged in a buffer, and an electric current is passed through the gel. Smaller fragments move faster and travel farther through the pores of the gel than larger fragments, so the fragments separate out by size into distinct bands.

Step 3: Visualisation:
After the run, the gel is stained (commonly with ethidium bromide) and viewed under UV light, where the separated DNA appears as a series of bands that can be compared to a size marker/ladder.

Final Answer:
Gel electrophoresis separates nucleic acid fragments by size using an electric field, producing bands that can be visualised under UV light after staining.