Biology · Biotechnology: Principles and Processes · NEET
DNA has phosphate groups in its backbone that carry a negative charge. When an electric field is applied across the gel, opposite charges attract, so the negatively charged DNA is pulled towards the positive electrode called the anode. This is why DNA never moves towards the negative electrode (cathode). NCERT states this clearly, so remember: DNA is negative, so it runs to the positive anode.
Smaller fragments move farther. The agarose gel acts like a sieve or a net with tiny pores. Large fragments get stuck and move slowly, while small fragments pass through the pores easily and travel a longer distance. So the smaller the fragment size, the farther it moves. This is the exact line NCERT uses and NEET has asked it directly.
The gel is made of agarose, a natural polymer extracted from sea weed. When set, agarose forms a matrix full of tiny pores that lets small DNA fragments pass and holds back big ones. This sieving property is the whole reason separation happens by size, so always link agarose to the sieving effect for NEET.
Pure DNA is colourless, so you cannot see it directly. The DNA is stained with a dye called ethidium bromide and then viewed under UV (ultraviolet) light. Under UV, the DNA-dye combination glows and appears as bright orange bands. Each band is a group of DNA fragments of the same size.
The separated bands of DNA are cut out from the agarose gel and taken out from the gel piece. This recovery step is called elution. The eluted, purified DNA fragments are then used to make recombinant DNA by joining them with cloning vectors. So the flow is: separate by electrophoresis, view under UV, then elute the required band.
What is the criterion for DNA fragments movement on agarose gel during gel electrophoresis?
Arrange the following steps of DNA fingerprinting in the correct sequence. A. Isolation of DNA and its digestion by restriction endonucleases. B. Hybridisation using a labelled VNTR probe. C. Transferring of separated DNA fragments to synthetic membranes. D. Detection of hybridised DNA fragments by autoradiography. E. Separation of DNA fragments by electrophoresis.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
After a restriction enzyme cuts DNA, you get a mixture of many fragments of different sizes. Gel electrophoresis separates them by size so you can identify and recover the exact fragment (the gene of interest) you want to clone.
The anode is the positive electrode and the cathode is the negative electrode. DNA, being negatively charged, always moves towards the positive anode.
DNA is stained with ethidium bromide and viewed under UV (ultraviolet) light, where it shows up as bright bands. This exact pairing is a common NEET one-liner.
Separation is the movement and sorting of DNA fragments by size inside the gel. Elution is the later step where a chosen band is cut out and the DNA is extracted from that gel piece for further use.
Yes, in reality proteins can also be separated by electrophoresis, but for NEET Biotechnology the focus is on separating DNA fragments by size using an agarose gel.
