How Does it Work?
Read the descriptions below to assist you with your conclusion questions:
Strawberries:
Strawberries are the DNA source for this protocol. Ripe strawberries are great for extracting DNA because they are easy to pulverize and contain enzymes called pectinases and cellulases which help break down cell walls. Another important point about strawberries is that they have enormous genomes. They have eight copies of each chromosome (octoploid) which means there is a lot of DNA to isolate within a strawberry.
Detergent:
The purpose of the detergent or dishwasher soap is to help dissolve the cell membrane. Detergent contains sodium laurel sulfate, which cleans dishes by removing fats and proteins. It acts the same way in the DNA extraction protocol, pulling apart the fats (lipids) and proteins that make up the membranes surround the cell and nucleus. Once these membranes are broken apart, the DNA is released from the cell.
Soap molecules and grease molecules are made of two parts:
- Heads, which like water (hydrophilic)
- Tails, which hate water (hydrophobic)
Both soap and grease molecules organize themselves in bubbles (spheres) with heads outside to face the water and tails inside to hide from the water.
Sodium Chloride:
Sodium chloride, also known as salt, helps to remove proteins (histones) that are bound to the DNA. It also helps to keep the proteins dissolved in the aqueous layer so they do not precipitate in the alcohol along with the DNA.
Ethanol or isopropyl alcohol:
DNA is not soluble in ethanol. When molecules are soluble, they are dispersed in the solution and therefore are not visible. However, when molecules are insoluble, they clump together and become visible. Therefore, by using a chilled alcohol the DNA will precipitate and be visible in this experiment. The colder the alcohol the less soluble DNA becomes. Besides allowing us to see the DNA, the alcohol separates the DNA from the other cell components, which are left behind in the water solution.