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#DNA precipitation

3 public questions tagged with this topic.

DNA & RNA isolation

In alcohol precipitation, DNA becomes less soluble because it is:

In alcoholic precipitation, DNA hydration is critical for solubility. Water molecules form hydration shell around negatively charged phosphates, keeping DNA hydrophilic and soluble. Addition of ethanol lowers dielectric constant of medium, reducing water activity and allowing monovalent cations to neutralize phosphates. This strips hydration shell, exposes hydrophobic nitrogenous bases, and makes DNA more hydrophobic and less soluble in polar solvent. Aggregation and precipitation follow. DNA does not become more hydrophilic, denatured at room temperature precipitation, or ionized further; hydrophobicity increase drives insolubility and aggregation in alcohol.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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DNA & RNA isolation

Ethanol helps in DNA precipitation by:

Ethanol precipitates DNA by altering solvent properties. Water has high dielectric constant of 80, shielding electrostatic attraction between negative phosphate groups and positive cations like Na+. Ethanol has dielectric constant around 24, dramatically lowering solvent polarity when mixed. This allows sodium ions from added salt to neutralize phosphate charges efficiently, reducing hydration shell and DNA solubility. DNA becomes less hydrophilic, aggregates, and precipitates. Ethanol does not lower pH significantly, increase hydrophilicity, or break disulfide bonds; its action is purely through dielectric and solubility reduction enabling aggregation.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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DNA & RNA isolation

The main basis for alcohol precipitation of DNA is:

Alcohol precipitation of DNA exploits solubility differences modulated by dielectric constant. DNA is soluble in water due to hydration of its negatively charged phosphate backbone. Addition of monovalent salt like sodium acetate neutralizes charges, while ethanol or isopropanol, having much lower dielectric constant than water, reduces the shielding of electrostatic interactions, allowing Na+ to bind phosphates. This decreases hydrophilicity and causes DNA to fall out of solution and precipitate. Charge repulsion is overcome, not increased, and pH shift or denaturation is not the primary mechanism for precipitation.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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