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I am working on an at home Isolation of DNA lab. Why was salt added to the DNA mixture is my current question?
a. Saltwater extracts DNA faster than tap water.
b. Helps to break open the cell.
c. Sodium cation and chloride anion will form an ionic compound with the other components of the cell.
d. The salt wasn’t really necessary.
PART OF DIRECTIONS BELOW
1. Using the knife and cutting board, cut your DNA source into small pieces.
2. Transfer DNA source to a small wide-mouth glass.
3. Using a fork or mortar and pestle, mash the pieces of DNA source against the sides of the glass until you have a liquid mush. (You may use a blender to mash the DNA source and blend together the shampoo, salt and water with the DNA. Blending must be very brief (three pushes of the button) because blending can rapidly break the DNA into shorter lengths.)
4. Add equal amount of water, several squirts of shampoo and about ½ teaspoon of salt. Stir to mix.
5. You should notice that the mixture is getting very thick. This is because the cell membranes are broken apart by the shampoo/salt combination, releasing the nucleic acids, proteins and other components of the cell. The DNA makes the solution very viscous.
Expert Answer
Solution:
The correct option is
c. Sodium cation and chloride anion will form an ionic compound with the other components of the cell.
Expalnation:1. The salt enables the DNA strands to stick together or “precipitate”. The positive charge of the sodium interacts with the negatively charged phosphate groups at the 5’ ends of DNA strands to neutralize the molecule – this helps to make the DNA less soluble in the water/alcohol mixture.
2.Because each nucleotide of the DNA molecule possesses a negatively charged phosphate group, DNA is a negatively charged molecule. Therefore, DNA molecules are not attracted to each other but are repelled by the like charges they possess. Adding salt (NaCl) to a solution containing DNA neutralizes the negative charges of the DNA molecule, making the separate DNA molecules more likely to collect together (precipitate) and become visible. Salt is able to do this because the sodium and chloride ions separate in solution and the positive sodium ions (Na+) are attracted to the negative charges of the DNA’s phosphate groups, thus neutralizing the negative charge.
