Extracting and precipitating DNA from cheek cells

Introduction:
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)

Making yogurt out of pasteurized milk and yogurt bacteria while testing Koch's postulates

Introduction:
a) Koch's postulates are... 1. Isolate a microbe that can be found in all sick people (in this case the "sick people" is yogurt) but not in healthy people ("healthy people" = milk). 2. Culture that microbe. 3. Inoculate the healthy people with the microbe. 4. Culture the microbe from the new sick people and it should be the same microbe as the original one. The microbe, or bacteria, that we will be using in this experiment is yogurt bacteria. Bacteria are prokaryotes, meaning they do not have a nucleus to hold their DNA. Bacteria can be both good and bad. E. Coli are bacteria that live in our intestines and help us digest food, which is very beneficial to us. Other bacteria however can cause disease and antibiotics can be taken to kill these harmful bacteria. Yogurt bacteria are a good kind of bacteria - they help with digestion and promote general good health. Yogurt bacteria break down milk sugar (lactose) into pyruvic acid, and then, using enzymes, the pyruvic acid is broken down into lactic acid. The lactic acid causes the milk to be more acidic, thus denaturing the milk protein casein into a more solid form - yogurt!
b) The purpose of this experiment is to make yogurt out of milk and yogurt bacteria. We will also be testing Koch's postulates using microbial techniques (extracting and culturing bacteria and identifying if the bacteria are the same).
c) We will be culturing bacteria using specific techniques. We will be using sterile inoculating loops to transfer yogurt bacteria from the petri dish to the test tubes. Precautions will be taken to avoid contamination, such as keeping the lab area clean and not touching the inoculating loops to any potentially contaminating surfaces. A vortex will be used to thoroughly mix the contents of each test tube and an incubator will encourage the production of yogurt overnight.
d) The controls of this experiment are the milk only tube (negative control) and the milk + yogurt bacteria tube (positive control). The variables are the milk + yogurt + ampicillin tube, and the milk + E. Coli tube. I think the negative control will do nothing and the positive control will produce yogurt (as should happen). The first variable should not produce yogurt because the ampicillin will kill the yogurt bacteria which are necessary to denature the milk into yogurt. The second variable will probably result in some of the milk being digested by the E. Coli, because that's what E. Coli do - digest food.

Procedure:
See video posted.

Results/Observations:

Discussion:

a) Tube #1, the negative control which contained only milk, obviously did not turn into yogurt because it did not have the yogurt bacteria in it. The sour, tainted milk smell is the result of unrefrigerated milk gone bad - it did not have the yogurt bacteria which helps preserve freshness. Tube #2, the positive control, turned into yogurt, as expected. The acidity of 4 can be attributed to the lactic acid, which was created by the breakdown of lactose and pyruvic acid (see Introduction part "a"). Tube #3 did not produce yogurt and turned out sour because the ampicillin killed all the yogurt bacteria, which are essential in the creation of yogurt. Tube #4, which served to test whether or not any type of bacteria can create yogurt out of milk, did nothing - the milk turned rotten and stayed in liquid form. This proved that the E. Coli does not produce yogurt out of milk and clearly, yogurt bacteria is the necessary ingredient for this reaction to take place.
b) Some possible sources of error include...

• Outside bacteria getting into the solution
• Not enough yogurt bacteria, ampicillin, and/or E. Coli being added to the appropriate tube
• Milk improperly pasteurized