Lab+4+DNA

__**Exercise 1. DNA Replication**__ 1. The following picture shows the unwinding of the super coiled DNA (red and green pipe cleaners) because of the topoisomerase. The white pipe cleaner wraped around the DNA serves as the topoisomerase. This enzyme clips the backbone which leads the DNA to un-coil.

2. The following picture shows how the helicase works in the enzymes of DNA replication. The helicase (white pipe cleaner) is located in between the two strands of DNA. The helicase uses ATP energy to melt the hydrogen bonds that keep the strands together.

3. The following picture shows how the enzyme, primase, works in DNA replication. The primase (light brown bead) is located next to the helicase and "primes" the DNA for replication. It is primed because of the -OH it provides which helps the DNA polymerase to attach to the nucleotide.

4. The following picture shows how the enzyme, DNA polymerase, works in DNA replication. There are two DNA polymerase ( the other light brown bead and dark brown bead) which are on each of the replicated DNA strands. The job of the DNA polymerase is to form the new covalent backbone bond for the phosphates and sugars. It also is used to guide the remaining nucleotides to bond correctly together.

5. The following picture shows how the enzyme, ligase, works in DNA replication. The ligase (small, neon green bear) is used to form covalent bonds between sugars and phosphates where there are gaps. For instance, when the RNA primer is removed.

__**Exercise 2. DNA Extraction**__ "DNA Extraction from Wheat Germ"

Three ways to prove that the substance is actually DNA:
 * "DNA"**

1. Acridine orange- This is a nucleic acid with a fluorescent cationic dye. If it interacts with the substance by intercalation or electrostatic attractions then it is DNA. It is a toxic process. []

2. DAPI- This is a fluorescent nuclear stain which uses an ultraviolet light. If the substance turns out to be actual DNA there will be a strong blue fluorescence visible. It is a non-toxic process. []

3. Ethidium bromide- This is a method that provides a fluorescent red-orange stain if DNA exists. However, it will only stain cells that are in their final stages of apoptosis (cells with much more membranes). Most ethidium bromide is below the level to be considered toxic. []

__**Exercise 3. Mitosis and Meiosis**__ The picture below shows the 2N-4N-2N lay out

The picture below shows the 2N-4N-2N-1N lay out