How does DNA travel in gel electrophoresis?

In gel electrophoresis, DNA molecules are negatively charged due to their phosphate backbone. When an electric field is applied, DNA will migrate towards the positively charged electrode, which is located at the opposite end of the gel from where the DNA samples are initially loaded. This movement occurs because oppositely charged particles attract each other—negatively charged DNA is pulled toward the positive electrode.

As DNA travels through the gel, smaller fragments can move more easily through the porous matrix of the gel compared to larger fragments, leading to separation based on size. This principle is widely used in molecular biology for analyzing DNA samples, such as in techniques for genetic fingerprinting, cloning, and checking the size of DNA fragments after restriction enzyme digestion.

The other options, such as DNA traveling towards the negatively charged plate or randomly within the gel, do not align with the fundamental principles of how charged particles behave in an electric field. Additionally, the assertion that DNA does not move at all contradicts the core purpose of gel electrophoresis, which is to visualize and separate DNA based on size.