Question

DNA fragments generated by the restriction endonucleases in a chemical reaction can be separated by
(a) Polymerase chain reaction
(b) Electrophoresis
(c) Restriction mapping
(d) Centrifugation

Answer 1

Hint: The DNA fragments are separated by a process that involves the application of an electric field to cause the DNA fragments to migrate into an agarose gel. It is used in laboratories to separate macromolecules based on size. The technique applies a negative charge so proteins move towards a positive charge.

Complete answer:
The DNA fragments are separated by electrophoresis, a process that involves the application of an electric field to cause the DNA fragments to migrate into an agarose gel. The gel is then stained with a methylene blue stain to visualize the DNA bands and may be photographed. Electrophoresis is used extensively in DNA, RNA, and protein analysis.

It is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. The endonuclease is an enzyme that cuts DNA at or near specific recognition nucleotide sequences known as restriction sites. Suspended particles have an electric surface charge, strongly affected by surface adsorbed species, on which an external electric field exerts an electrostatic Coulomb force.

Additional Information:
- According to the double layer theory, all surface charges in fluids are screened by a diffuse layer of ions, which has the same absolute charge but opposite sign concerning that of the surface charge.
- The electric field also exerts a force on the ions in the diffuse layer which has a direction opposite to that acting on the surface charge.
- This latter force is not applied to the particle, but the ions in the diffuse layer located at some distance from the particle surface, and part of it is transferred to the particle surface through viscous stress.

Note:
- This part of the force is also called electrophoretic retardation force.
- When the electric field is applied and the charged particle to be analyzed is at steady movement through the diffuse layer, the total arising force is zero.
- An electrophoretic system consists of two electrodes of opposite charge (anode, cathode), connected by a conducting medium called an electrolyte.