NaCl, or sodium chloride, is used in DNA extraction primarily to remove proteins that are bound to the DNA and to help keep those proteins dissolved in the aqueous solution, preventing them from precipitating along with the DNA.
Here's a more detailed breakdown:
Role of NaCl in DNA Extraction
1. Protein Removal
- Neutralizing Charges: DNA is negatively charged due to the phosphate groups in its backbone. Proteins, which may be positively charged or have positively charged regions, can bind to DNA through electrostatic interactions. NaCl provides Na+ (sodium) ions, which shield the negative charges on the DNA, disrupting the ionic bonds between DNA and proteins. This allows the proteins to be separated from the DNA.
- Disrupting Protein Structure: High salt concentrations can also disrupt the hydrophobic interactions within proteins, causing them to unfold or denature. Denatured proteins are less likely to bind to DNA and more likely to stay dissolved in the aqueous solution.
2. Preventing Protein Precipitation
- Solubility: After proteins are detached from the DNA, the presence of NaCl maintains their solubility in the aqueous solution. This prevents them from precipitating out of solution during the subsequent alcohol precipitation step, ensuring a purer DNA sample. Without sufficient salt, proteins could co-precipitate with the DNA, leading to a contaminated sample.
Summary
In essence, NaCl acts as a buffer, controlling ionic strength and preventing unwanted protein-DNA interactions and protein precipitation during DNA extraction, leading to a cleaner DNA sample.
