Year 11 Human Biology - DNA Extraction

why do we crush the fruit first

crushing the fruit breaks open many of the cell walls, which releases the nuceli where the DNA is stored

what does the detergent do in the buffer

the soap within the detergent breaks down the fatty membranes of the cells and breaks open the nuclear membrane which releases the DNA into the solution

what does the salt in the buffer do

the salt makes the DNA molecules stick together, separating the DNA from the proteins that are also released from within the cell

why do we cool the solution whilst crushing it

by cooling the solution we are protecting the DNA by ensuring that enzyme activity does not increase. Because the DNA is not protected by the nuclear membrane, enzymes can acces it but the cooling helps slow these enzymes down.

why do we pass the solution through a gauze

the gauze retains the debris of the strawberry cell. As the DNA is dissolved in the extraction buffer it will pass throught the gauze but the debris will not

why does DNA collect at the interface

when we add the alcohol we form 2 layers, the extraction buffer below and the alcohol on top. where these 2 layers meet DNA will collect because DNA is insoluble in alcohol and hence it precipitates.

why is it imprtant that the alcohol is cold

by the alcohol ebing cold it helps the DNA to solidify and precipitate

what causes DNA to have different melting temperatures

the hydrogen bonds between A-T are weaker than those between C-G. Hence if a strand of DNA has more A-T bonds it will melt at a lower temperature, and vice versa.

what charge does DNA have

negative

what is a method to determine how much DNA is in a solution

pass a UV light through the solution and measure the absorbance of the light. DNA absorbs UV light so if more DNA is present, more UV light will be absorbed and less light will be detected.

why is DNA stable

because it has to be subject to very high temperatures for it to denature and when the temperatures lower it will rejoin into 1 molecule