In a standard DNA extraction protocol, what is the primary purpose of adding isopropyl alcohol to the lysate?

• A. To precipitate DNA out of solution so it can be collected as a visible pellet or strands
• B. To denature and digest proteins using protease activity
• C. To lyse the cell membrane by dissolving phospholipids and releasing DNA
• D. To chelate $M^2$ ions (e.g., ${\mathrm{Mg}}^2$) and inhibit nucleases

Answer: (A)

Verified step by step guidance

1. Understand that during DNA extraction, the goal is to isolate DNA from other cellular components in the lysate solution.
2. Recognize that DNA is soluble in aqueous solutions but becomes less soluble in the presence of alcohols like isopropyl alcohol.
3. Know that adding isopropyl alcohol causes DNA molecules to aggregate and precipitate out of the solution because alcohol reduces the dielectric constant of the solution, decreasing DNA solubility.
4. This precipitation allows the DNA to be seen as a visible pellet or strands, which can then be separated by centrifugation or spooling.
5. Therefore, the primary purpose of adding isopropyl alcohol is to precipitate DNA so it can be collected, not to denature proteins, lyse cells, or chelate metal ions.