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During the purification process for recombinant DNA technology, addition of chilled ethanol precipitates out:
After removing RNA with ribonuclease and proteins with protease, addition of chilled ethanol causes purified DNA to precipitate out as a collection of fine threads, which can be spooled out! Match Option (2)!
To obtain pure genetic material, bacterial, fungal, or plant cells are treated with specific lytic enzymes (cellulase/chitinase/lysozyme), followed by enzymatic degradation of all non-DNA polymers:
Because DNA is a highly charged polyanion with a negatively charged phosphodiester backbone, it is soluble in water. Addition of ice-cold ethanol significantly lowers the dielectric constant of the solvent, causing sodium ions to neutralize phosphate charges and forcing DNA out of aqueous solution:
The precipitated DNA aggregates into visible fine fibrous white threads that can be wound up around a glass rod in a procedure termed spooling.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
RNA is previously degraded into soluble ribonucleotides by treatment with ribonuclease (RNase) prior to ethanol addition.
Addition of chilled ethanol specifically precipitates pure DNA as visible fine threads.
Histones and other proteins are digested by protease enzymes during prior purification steps.
Polysaccharides are degraded by cellulase/amylases or removed during organic washes.
Students confuse which reagent treats which molecule: Ribonuclease removes RNA; Protease removes proteins; Chilled ethanol precipitates DNA.
"DNA that separates out can be removed by spooling, after addition of chilled ethanol which precipitates purified DNA as a collection of fine threads."
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