Question

During the isolation of genetic material, the chemical used to precipitate out the purified DNA is
A. Bromophenol blue
B. Chilled ethanol
C. Ethidium bromide
D. Both A and C

Answer 1

Hint: Isolation of genetic material is the process of acquiring plasmid DNA or genomic DNA in the pure form from bacterial cells or host cells respectively.

Complete step-by-step answer:
To achieve this, the cells are first exposed to enzymes such as cellulase, lysozyme, or chitinase, etc. to dissolve the cell wall. Sometimes organic solvents such as ether, alcohols, or chloroform can interfere with the cell wall by permeabilising cell membranes and cell walls. This releases DNA along with other cellular macromolecules like proteins, RNA, lipids, and polysaccharides. The second phase is the elimination of the other macromolecules using suitable enzymes like ribonucleases for digesting RNA, proteases for digesting proteins, etc.

The third phase is the precipitation of purified DNA from the medium. This is done by using chilled ethanol. DNA is a polar molecule because of negative charges on its phosphate backbone. Therefore, it is easily soluble in water. Chilled ethanol has less permittivity and allows easy bonding among the negative charges on the phosphate backbone of DNA and any positive ion exists in the extraction solution that makes up stable ionic bonds. Hence, the solubility and polarity of DNA are lost, and it easily precipitates.

Loading dye is used to load DNA samples into agarose gel wells and track migration during electrophoresis. During agarose gel electrophoresis bromophenol blue is often used as a tracking dye. The bromophenol blue and DNA being negatively charged, move towards the positive electrode during gel electrophoresis.

Ethidium bromide is fluorescent dye used in order to stain DNA. It binds to DNA and on being exposed to UV radiations, the dye fluoresces, and the DNA fragments can be seen as orange bands.

Therefore the correct answer is option B.



Note: The purified DNA, after treatment with different enzymes, precipitates out after the addition of chilled ethanol. This is treated as a collection of fine threads in the suspension and is easily gathered. The process is called DNA spooling.