Which DNA fragment bands moved faster and farther in a gel electrophoresis?

Which DNA fragment bands moved faster and farther in a gel electrophoresis?

• A. Larger fragments move slower.
• B. Smaller fragments move faster and farther.
• C. DNA fragments move at the same speed regardless of size.
• D. Only circular DNA migrates in gel.

Answer: (B)

Gel electrophoresis separates DNA by size because the gel acts as a sieve. DNA is negatively charged, so under an electric field it moves toward the positive electrode. Smaller fragments navigate the gel pores more easily and experience less friction per base pair, so they travel faster and farther than larger fragments in the same amount of running time. As a result, the smaller DNA pieces end up farther down the gel than the larger ones. A DNA ladder is used to estimate sizes based on how far fragments have migrated.

Gel electrophoresis separates DNA by size because the gel acts as a sieve. DNA is negatively charged, so under an electric field it moves toward the positive electrode. Smaller fragments navigate the gel pores more easily and experience less friction per base pair, so they travel faster and farther than larger fragments in the same amount of running time. As a result, the smaller DNA pieces end up farther down the gel than the larger ones. A DNA ladder is used to estimate sizes based on how far fragments have migrated.