Question

DNA EXTRACTION & PURITY PROTOCOL

1. Add a small piece of peeled banana (2-3 cm) and 12mL extraction buffer (NaCl & Sodium Citrate) into the beaker. This buffer contains salts necessary for the precipitation of the DNA. The ions in the solution make it more polar facilitating the dissolving of the DNA.
2. Add 3mL detergent into the beaker. This will break open the cells and dissolve the DNA. Detergent breaks up the lipids of the plasma and nuclear membranes

Questions:

a. Why does a more polar solution make DNA more likely to dissolve?

b. How does detergent break up lipids in a membrane?

Answer 1

a) The solubility of DNA depends upon the polarity of the solution. Higher the polarity, more will be the solubility. This is because of the fact that the DNA is a polar molecule. It's sugar-phosphate backbone is highly charged (hence polar) due to the presence of Phosphate group and Hydroxyl group. Since it is a common fact that like dissolves like, so polar molecules will always be soluble in polar solvents. Increasing the polarity of solution will consequently increasing its polarizability, hence enhancing the dissolution.

b) Detergent breaks up the lipids in a membrane by forming micelles. Detergents contain a long non-polar tail and a short polar head. Firstly they penetrate the lipid membrane and then break the interactions between constituent lipids by denaturing them, hence making them fragmented. Now these small fragments are solubilized by the non-polar tails of the detergents, forming small aggregates called micelles. It ultimately results in formation of detergent-micelle complex, which is then later washed away with water. That's how detergents break the lipid membranes.

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