What does gel electrophoresis separate, and how is it used in biology labs?

• A. RNA by length
• B. DNA fragments by size using an electric field
• C. Proteins by charge only
• D. Lipids by hydrophobicity

Answer: (B)

Gel electrophoresis uses an electric field to move charged molecules through a gel. DNA has a negative charge, so when voltage is applied, fragments migrate toward the positive electrode. The gel’s porous matrix acts like a sieve, slowing larger fragments more than smaller ones, so DNA fragments separate by size as they travel. In biology labs, this lets you check that PCR products or restriction digests are the expected lengths, estimate fragment sizes by comparing to a DNA ladder, and sometimes purify specific fragments for further experiments. To see the bands, the gel is stained with a dye that binds DNA and viewed under light.