Lab+4+-+DNA

=__Lab 4 - DNA__=

=__Exercise 1: DNA Replication__=

1. **//Topoisomerase//**: In this stage (white bead), this enzyme unwinds the DNA by clipping the DNA backbone. As depicted in the picture, the white bead demonstrates this enzyme splitting the coils. It clips and loosens.

**PICTURE**:

2. **//Helicase//**: In this stage, this enzyme (the bigger bead) goes into the loosened gaps (from the first stage), and unzips the gene all the way.

**PICTURE**:

3. **//Primase//**: In this stage, this enzyme makes a short RNA segment, called "primer" (white pipe-cleaner), which enters and primes the DNA strips for replication, providing an - OH for the 4th stage to occur (or DNA polymerase able to attach to the original DNA nucleotide). Later, this primer will be replaced by DNA nucleotides.

**PICTURE**:

4. **//DNA Polymerase//**: In this stage, DNA Polymerase, a multifunction enzyme, guides the nucleotides to bond with their complements (A-T, G-C), and creates the covalent bond backbone between sugars and phosphates. Notice, in this picture, the newly-bound strands (although also note the gaps still present...)

**PICTURE**:

5. **//Ligase//**: In this stage, this enzyme entirely forges the covalent bonds between sugars and phosphates where there have been gaps left from RNA primer. Notice, in this picture, the completely-bound DNA strands, now replicated!

**PICTURE**:

=__Exercise 2: DNA Extraction__=


 * PICTURED ABOVE:** //DNA Extraction from Wheat Germ.//

1. The first way to test DNA is to use Ethidium Bromide (EtBr) staining, which is an "intercalator" that inserts itself in the spaces between the base pairs of the double helix. With UV absorbance, (http://nationaldiagnostics.com/article_info.php/articles_id/70), the EtBr "illuminates" the DNA a yellow/orange color. The UV light could potentially damage the DNA, though. EtBr is very toxic, and should be handled with care.
 * //Three ways to prove DNA://**

2. The second way to test DNA is with Crystal Violet. Similar to EtBr, Crystal Violet inserts itself in the spaces between the base pairs of the double helix. It's less dangerous than EtBr, and scientists do not need to use UV light to detect the DNA. (http://www.ncbe.reading.ac.uk/dna50/staining1.html)

3. The third way to test DNA is with** methylene blue, which bind ionically with the nucleic acids and stain the DNA. The gel in DNA testing, though, can also get stained by methylene blue, so extra work called destaining may need to occur to see the results more clearly. Methylene blue has caused illness in some cases but is not deathly toxic. Today, even, it is being tested as a treatment for malaria and even cancer. (http://en.wikipedia.org/wiki/Methylene_blue). **

=__Exercise 3: Mitosis and Meiosis__=

__MITOSIS__:

Depicted above: 2N - 4N - 2N; Homologous chromosome lining up individually at equatorial line (third phase down with green beads), then cell division by end.

__MEIOSIS:__

Depicted above: 2N - 4N - 2N - 1N; Crossing over occurring in the third stage down, then cell division 1, then by the end, cell division 2.

__**SOURCES**__: An aggregate of lab instructions, explanations and pictures, lab instructor,