CUET UG Biology MCQ Practice

Gel electrophoresis is a technique used to separate DNA fragments based on their size. The correct sequence of steps is:

Step 1: Moving of DNA fragments towards the anode (C)
DNA fragments carry a negative charge due to their phosphate backbone.
When an electric field is applied, they migrate through the agarose gel towards the positively charged anode.
Smaller fragments move faster and travel farther than larger ones.
Step 2: Staining with ethidium bromide (B)
After electrophoresis, the gel is stained with ethidium bromide (EtBr).
Ethidium bromide intercalates between DNA base pairs, making the DNA visible under UV light.
Step 3: Exposure to UV light (A)
The stained gel is exposed to ultraviolet (UV) light.
DNA bands fluoresce and become visible, allowing the separated fragments to be identified.
Step 4: Elution (D)
The desired DNA fragment is cut from the gel and extracted.
This process of recovering DNA from the gel is called elution.