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Electrical charge is a property of matter. It is measured using the SI unit, the coulomb (C). From a biological stand-point, this is most useful when referring to the charge of ions or molecules (like Mg2+ ions having a 2+ charge, or DNA having partial negative charge).

If any object with a charge is placed in a magnetic field they will experience a force (be that repulsive or attractive). This force is proportional to the strength of the magnetic field and the size of the charge.

If two charged objects come together, they will also experience a force, as stated previously. This is called the coulomb force and is mathematically described as so:

F = q1q2/4π(ε0)r2 [1]

Where F = Force

q1 and q2 = respective charges

ε0 = Permittivity of free space (8.85x10-12 Fm-1)

r = distance between centre of objects   

Charge is an exploitable property when working with DNA. The phosphate backbone of DNA carries a partial negative charge which, in the presence of an electric field, can migrate down a gel. This is the concept of gel electrophoresis. Smaller fragments of DNA will migrate further down the gel, towards the anode, than larger fragments. Using a DNA ladder of predetermined sizes of DNA, you can work out the size of unknown fragments using the distance they have moved down the gel.[2]


  1. R. Nave. Electric Forces. Available from: Date accessed: 18/10/16
  2. University of Waikato. Gel Electrophoresis. Available at: Date accessed: 18/10/16
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