What tool does one use to seperate DNA fragments?

Question

A. an electron microscope

B. a cyclotron

C. a mass spectrograph

D. a polyacrylamide gel

E. a centrifuge (high speed)

Answer 1

Answer: D

DNA, or deoxyribonucleic ACID, is a polyanionic substance. Different fragments of DNA vary because they are of different lengths. Consequently, they have different masses (needles to say, longer fragment have a larger mass then shorter ones) Also remember that the longer a particular strand, the more negative charge it will have. Electrophoresis is a process where a certain electric field is applied over the "migration area." The force applied is constant throughout the area, we known that force = mass X acceleration, acceleration = force / mass. Larger segments of DNA will have greater mass and hence move less in a given force as compared to a smaller segment with less mass.

Answer 2

The correct/best answer is D.

E will seperate DNA from other cell constituents, but it is not a good method of seperating strands of DNA. The reason is becasue iafter centrifuging, the strands will all be roughly in the same spot in the medium.

After cetrifuging, isolate the DNA sample and run it through the polyacrylamide gel; a process called electrophoresis. This will seperate the stands based on the fragment size. Smaller strands will be further ahead in the gel, closer to the anode (+'ve side).

Answer 3

According to 'Oxford Journals - Nucleic Acids Research'  

DNA fragments containing mispaired and modified bases, bulges, lesions and specific sequences have altered conformation. Methods for separating complex samples of DNA fragments based on conformation but independent of length have many applications, including (i) separation of mismatched or unmatched DNA fragments from those perfectly matched; (ii) simultaneous, diagnostic, mismatch scanning of multiple fragments; (iii) isolation of damaged DNA fragments from undamaged fragments; and (iv) estimation of reannealing efficiency of complex DNA samples....