a) All living things contains DNA in each of their cells. Eukaryotes contain a nucleus inside their cells, which houses the DNA. Prokaryotes do not have a nucleus, but their DNA moves freely throughout the cell. DNA is a double-stranded helix composed of sugar (deoxyribose), phosphates, and bases (thymine, adenine, guanine, and cytosine). Thymine pairs with adenine and guanine pairs with cytosine. Genes are particular segments of DNA which code for a specific protein. Proteins are what give your eyes color, carry out cell communication, and build muscles.
b) The purpose of this lab is to precipitate (or anti-dissolve) DNA, so that we can see and observe it with the naked eye. In a professional setting, such as in a biotech lab, one can use the extracted DNA to map the genome, clone genes, compare DNA, test for genetic diseases, or do forensics. However, in the classroom, we will simply be admiring our DNA.
c) We will use a "chewing on the insides of our cheeks" technique in order to loosen cheek cells. The saline solution (which contains 0.9% salt water) will be used to give the cells an isotonic solution to keep them from bursting or shriveling. The lysis buffer (which is a detergent) will serve to dissolve the cell membranes (which are made of phospholipids), releasing the DNA out into the open. DNase is an enzyme that lives in the cell in order to kill foreign DNA; however, we do not want the DNase to kill our own DNA now that it's been released, so we add the enzyme protease to destroy it. DNA is negatively charged, due to the negative phosphates. A negative charge makes DNA polar and hydrophillic, meaning it likes water and will dissolve in it. We do not want our DNA to dissolve - in fact, we want to anti-dissolve it or precipitate it - so, we add Na+ ions to give DNA a neutral charge. This makes DNA nonpolar and hydrophobic so it will not dissolve. The hot water bath serves to speed up the enzyme reactions and helps break open the cell membranes (lysis buffer works better with hot water). Finally, the cold ethanol (rubbing alcohol) helps with precipitation by forming a very cold layer on top of the hot water solution.
Procedure:
*Our video was accidentally deleted by another group - however I will briefly go over the procedure here.
See Introduction part "c" for details on each step of the procedure. However, I will note that after the DNA had precipitated entirely, we extracted it with a pipette and put it into a necklace and wore it around school!
Results/Observations:
I observed that almost instantly after we added the cold ethanol to the hot water solution, the DNA began precipitating between the two layers. It formed a stringy, white substance that was very easy to see and very cool! It definitely looked like DNA, with the long strands all tangled together. It was very interesting.
Discussion:
a) I did not get very much DNA, however, it was definitely there and very easy to see. The procedure largely explains how the DNA was extracted and there is not anything to analyze or explain really about the results. All I can say is that it worked!
b) Possible sources of error could be...
- Food or other contents from the mouth could have gotten into the solution
- Insufficient chewing on the cheeks may not have extracted enough cheek cells
- Some DNA may have been destroyed in the process by a hypo/hypertonic solution (if the saline solution did not work) or DNase (if the protease did not kill it in time)
