Discussion of all aspects of biological molecules, biochemical processes and laboratory procedures in the field.
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The process is called electrophoresis, described in a section of this site:
Separation of ionic molecules, (principally proteins) by the differential migration through a gel according to the size and ionic charge of the molecules in an electrical field. High resolution techniques normally use a gel support for the fluid phase.
Examples of gels used are starch, acrylamide, agarose or mixtures of acrylamide and agarose. Frictional resistance produced by the support causes size, rather than charge alone, to become the major determinant of separation.
Smaller molecules with a more negative charge will travel faster and further through the gel toward the anode of an electrophoretic cell when high voltage is applied. Similar molecules will group on the gel. They may be visualised by staining and quantitated, in relative terms, using densitometers which continuously monitor the photometric density of the resulting stain.
The electrolyte may be continuous (a single buffer) or discontinuous, where a sample is stacked by means of a buffer discontinuity, before it enters the running gel/ running buffer. The gel may be a single concentration or gradient in which pore size decreases with migration distance.
In SDS gel electrophoresis of proteins or electrophoresis of polynucleotides, mobility depends primarily on size and is used to determined molecular weight. In pulse field electrophoresis, two fields are applied alternately at right angles to each other to minimise diffusion mediated spread of large linear polymers.
and for those tests in which size is only a basis of separation . the charge/mass ratio of molecules is maintained same so the acceleration produced due to electrostatic force is same for all molecules at equal distance from electrodes And the retardation produced due to the frictional force of gel is only different for different molecules. frictional force is larger for larger molecules & smaller for smaller ones , this will give sizewise separation. The trick is - make the frictional force the basis of separation.
Also for DNA the charge to mass ration is nearly same , so U needn't add any reagent.
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