WIKI                                        DNA REPLICATION

In this lab you will:

LABORATORY OVERVIEW
EXERCISE 1. DNA REPLICATION
EXERCISE 2. MEIOSIS AND MITOSIS
 
EXERCISE 1.  DNA REPLICATION
Look around your house (or lab) and find materials that could be used to demonstrate how DNA replicates (pipe cleaners, beads, buttons, etc).  Use these to demonstrate physically to a person of your choice while explaining the sequence that the enzymes are used and the function of each enzyme. The combination of "doing" while "talking" is a learning trick that helps cements the information more firmly into memory. 
Take a picture of each step of your "setup", label and put this in your wikibook with an explanation of what is happening. (5 PICTURES) 
The Enzymes of DNA Replication

  1. Topoisomerase
- (toe-poe-i- SOM-er-ase) the "i" as in eye
This enzyme initiates the unwinding of the super coiled DNA by clipping the DNA backbone. 
SEE THE PICTURE. 

  2. Helicase
- (HE- li-case) the i in li is like in lick
This enzyme separates the double strand by "melting" the hydrogen bonds that hold the bases together.  It requires energy (in the form of ATP ). 

  3. Primase 
- (PRI- mase)the I is like "eye"
This enzyme makes a short RNA segment (called a primer) that is complementary to the DNA strand at specific sites.  It "primes" for DNA replication because it provides an - OH for DNA polymerase to attach the first DNA nucleotide.  The RNA primer is later removed and the gap is filled in with DNA nucleotides.  SEE THE PICTURE.

4. DNA polymerase (III- major polymerase)
- (pol- I- mer- ase) the "i" as in "him"
This is the multifunction enzyme that binds to one side of the DNA and 
a. guides nucleotides to bond with their complementary pair (A with T and G with C)
b. forges the covalent bonds of the backbone between the sugars and phosphates
SEE THE PICTURE. 

  5. Ligase
- (LYE - gase) 
This enzyme forges covalent bonds of the backbone between the sugars and phosphates. It does this where there is a gap, like when the RNA primer is removed. 

 

GO HERE TO DO A JAVA ON DNA REPLICATION

 
EXERCISE 2. MITOSIS AND MEIOSIS
Materials:  Use any materials at hand to demonstrate this like you did the DNA replication above. The cut pipe stem cleaners or soda straws can be used, or cut paper. 

Methods:
The point of this exercise is to work thru the duplication of chromosomes and division of the cell in mitosis.

This doesnt need to be complex.  (2) sets of 2 different colored short papers is all that is needed.  One color for the "old" DNA, 1 color for the "new" DNA. 


Lay out the 2N-4N-2N and 2N-4N-2N-1N arrangements, take  pictures and put in your lab wikibook. (2)
Mitosis is the division of somatic cells.  DNA replicates or doubles right before division takes place. Humans have 23 different chromosomes  numbered 1 - 22 and the 23rd is the X and Y chromosome. There are 2 copies per cell making the number of chromosomes = 46 or 2N.  Even tho the X and Y don't look alike, they share most of the same genes and are in fact a pair.  Chromosomes come in different lengths the placement of the centromere is not necessarily in the middle.  Once the DNA is replicated the 2 chromatids (copies) are attached at the centromere until pulled apart as the cell divides.

Do a search on youtube for a good example of mitosis. LINK TO IT FROM YOUR WIKI PAGE 

Meiosis is the division of gametic cells, eggs and sperm.  There are two important differences in meiosis. 

1. The first occurs after DNA is duplicated to the 4N number.  Both pairs of chromosomes (4N) line up and crossing over occurs, there is an actual exchange of chromosomal material. 

2. The second occurs after the first cell division to the 2N number there is another division to 1N number.  These cells are now ready to be fused with another gametic cell in fertilization and reconstitution into the 2N or normal number.
 
 

Do a search on youtube for a good example of meiosis.  LINK TO IT FROM YOUR WIKI PAGE 

sp