Question

Linear DNA fragments of sizes of 1500 bp, 3000 bp, 4000 bp and 4500 bp are obtained from gel electrophoresis. The position of these fragments from cathode to anode of the gel would be:

• A. 1500 bp, 3000 bp, 4000 bp, 4500 bp
• B. 4500 bp, 4000 bp, 3000 bp, 1500 bp
• C. 3000 bp, 4000 bp, 4500 bp, 1500 bp
• D. cannot be determined

Answer 1

The correct option is B 4500 bp, 4000 bp, 3000 bp, 1500 bp

Gel electrophoresis is a method that separates macromolecules like DNA on the basis of their charge and size by allowing them to migrate on a gel matrix. The DNA molecules are negatively charged due to the presence of phosphate groups in their constituent nucleotides. So, the DNA fragments, when loaded in the wells present in the gel near the negative electrode (cathode), will migrate towards the positive electrode (anode).

When we run the gel, the shorter DNA fragments having less molecular weight migrate through the gel more quickly than the longer ones. Therefore, a DNA fragment with 4500 bp will be nearest to the cathode and that with 1500 bp will be nearest to anode.