CSI: Crime Scene Investigation Lafayette

Background: Scientists today, use a bacterial defense mechanism called the restriction enzyme. A restriction enzyme is basically like a "restriction scissors" that make cuts at certain areas in a sequence of base pairs that are recognized by the enzyme. This enzyme has derived from viruses that eject their DNA into a cell, and use the restriction enzyme, as a bacterial defense. A restriction enzyme, basically slides down a DNA molecule, until it starts to recognize a specific sequence, this then causes the enzyme to stop sliding and cut the strand off that is recognized by the restriction enzyme. Once this happens scientists take this specific strand and place it into a process called agarose gel electrophoresis, which separates the strand so it can then be observed. This process is done, by placing the DNA fragments into an agarose gel slab, which is placed into a chamber filled with conductive buffer solution, then a direct current is passed between wire electrodes at each end of the chamber. Since DNA fragments are negatively charged, they are going to move towards the positive poles in the electric field. Once this happens, the agarose gel acts like a "molecular sieve" which smaller DNA fragments move easier than larger fragments. Some time after, the smaller fragments will have traveled further than the larger pieces, creating single bands of DNA at certain places, which are then stained so the bands can then be seen. This is just like DNA fingerprinting from crime scenes, but they use radioactive probes that are specific to certain nucleotide sequences and then compare the DNA of different people.

Agarose Gel Electrophoresis

Purpose: Our purpose for this lab is to figure out who committed the crime by using a forensic DNA
fingerprinting kit.

Lab instructions: 1. First we labeled micro test tubes CS (crime scene), S1 (suspect one), S2 (suspect two), S3 (suspect three), S4 (suspect four), S5 (suspect 5).
2. Then we took a DNA sample form each stock tube and placed the specific DNA samples in the corresponding tubes (using a 10 pipet).
3. Then we used a centrifuge to mix the components together.
4. Next we placed our tubes in a foam micro tube and incubated them overnight in 37 C water.
5. Then we added 5 hl of loading dye in each tube.
6. Then we added each sample in its specific well in the agarose gel, while it was in the electrophoresis apparatus with 275 ml of buffer solution.
8. After that, we turned on the electrophoresis chamber for 3 minutes and then turned off the apparatus.
9. Next, Mr. Chugh stained our agarose gel with 120 ml of 1x Fast Blast DNA staining it overnight.
10. The next day we saw our end results of our lab.

Observations and Results: Once our agrose gel was complete I could easily see deep blue strands of DNA in certain places on the gel. In our end results, we came to a conclusion that suspect 3 or Chloe had to have done the because, the DNA strands from suspect 3 (Chloe), was closely related to the one found at the crime scene. Though we were sure that our results were correct, we could have accidentally not put enough of the DNA in well # 3, since the DNA strands in 3 were very faint and hard to see where the location of the strands were in the agarose gel.