CSI: Lafayette-- Restriction Enzymes, Gel Electrophoresis, and One Lengthy Prison Sentence

Only the most talented criminals are capable of committing a crime without leaving a single source of DNA at the crime scene. DNA, the molecular name tag, is found in hair, blood, skin cells, saliva, semen, etc. Just one droplet of blood or a couple cells could help police identify who committed a crime. Science has made it much harder to be a bad guy.
   DNA profiling is done using Restriction Fragment Length Polymorphism (RFLP). The key to this technique is the restriction enzymes. Such enzymes are found in bacteria, where they are an intrinsic defense against bacteriophage viruses. When the bacterial cell detects foreign DNA from a virus, restriction enzymes cut the viral DNA at a specific, palindromic site, destroying the DNA. There are usually several of these sites at different locations on the DNA, varying from person to person. This is where RFLP comes into play. When restriction enzymes are used on human DNA they cut in different places, resulting in fragments of different sizes. This is how we differentiate between suspects.
   In our experiment, we will use restriction enzymes and gel electrophoresis to determine who committed a crime, comparing the five suspects' DNA to DNA recovered from the crime scene. The restriction enzyme we are using is from the bacteria E. coli. Because all the suspects have different DNA, the enzyme will digest the genes at different locations, creating fragments of different lengths (in base pairs).
   In order to actually see the differences in length, we use a process called gel electrophoresis. The agarose gel we will use is a matrix through which DNA can travel. Electricity is added to the gel, and the current is stabilized by a buffer. The DNA starts on the negative end, but because it has a negative charge, it slowly migrates to the positive side. Smaller fragments will travel further because they can more easily squeeze through the matrix. Conversely, larger DNA fragments (more base pairs) will not be able to travel as far. After running the gel, we will stain the DNA so it can be visualized
   We will run the DNA samples of all suspects, as well as the DNA from the crime scene. One of the suspect's DNA profiles should match the profile of the crime scene DNA, and that will let us know who is guilty. There will also be a marker that serves as a control to make sure the gel worked correctly.
   So, the only question is, WHO DUNNIT?