Question

Study the gel electrophoresis of the DNA sample given below and select the correct statement among the following.

• A. DNA fragment in band 1 has the largest size
• B. The DNA fragments in all the bands have same size
• C. DNA fragment in band 5 is more positively charged than that in band 1
• D. The DNA fragment in band 4 has the smallest size

Answer 1

The correct option is A DNA fragment in band 1 has the largest size

Gel electrophoresis is a method that separates macromolecules on the basis of their charge and size.
The DNA molecules are negatively charged due to the presence of phosphate groups in its nucleotides. So, the DNA fragments when loaded in the wells present in gel near the negative electrode (cathode), will migrate towards the positive electrode (anode).
When we run the gel, the smaller DNA fragments travel a longer distance from the negative electrode. Thus the fragements closer to the negative electrode are larger in size.
In the image given, DNA fragment in band 1 is closest to cathode, hence it can be concluded to have the largest size. All the bands are distinct in their positions, this means the DNA fragments have different sizes. Since DNA fragment in band 5 is located farthest from the negative terminal, it has migrated maximum distance. Hence, it is the smallest in size.