Why did bromophenol blue move farther than xylene cyanole despite weight differences?

Why did bromophenol blue move farther than xylene cyanole despite weight differences?

• A. Because it is smaller in size
• B. Because xylene cyanole is more branched
• C. Because the gel matrix slowed xylene cyanole
• D. Because bromophenol blue has a greater charge-to-mass ratio

Answer: (D)

In gel electrophoresis, how fast a molecule moves depends on the electric force acting on it relative to how much it resists that movement. That resistance comes from the molecule’s size and shape. The key factor here is the charge-to-mass ratio: a molecule with more charge per unit mass will experience a stronger push in the electric field for its size, so it travels farther in the same amount of time. Bromophenol blue has a greater charge relative to its mass than xylene cyanole, so it experiences a larger force per unit drag and moves farther despite being heavier. If it were just about being smaller or about the gel slowing one dye more due to shape, the result wouldn’t align as cleanly with the observed difference; the higher charge-to-mass ratio provides the best explanation for the greater migration.

In gel electrophoresis, how fast a molecule moves depends on the electric force acting on it relative to how much it resists that movement. That resistance comes from the molecule’s size and shape. The key factor here is the charge-to-mass ratio: a molecule with more charge per unit mass will experience a stronger push in the electric field for its size, so it travels farther in the same amount of time.

Bromophenol blue has a greater charge relative to its mass than xylene cyanole, so it experiences a larger force per unit drag and moves farther despite being heavier. If it were just about being smaller or about the gel slowing one dye more due to shape, the result wouldn’t align as cleanly with the observed difference; the higher charge-to-mass ratio provides the best explanation for the greater migration.