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POGIL: “DNA and its Uses”
A lesson on DNA extraction
Objectives:
1. Students will learn the function of DNA
2. Students will learn how DNA is contained within cells.
3. Students will learn how DNA can be isolated from cells by DNA extraction.
Read This:
DNA can be considered the hereditary “code of life.” DNA can be compared to a recipe or a list
of instructions on how to create a living organism. Almost all structure and function of living thins is
dependent on and determined by DNA.
MODEL 1:
Comparing genes to evaluate
similarity among organisms
…AGCUAAAGCUA… Gene sequence #1 human
…AACUAAACCUG… Gene sequence #2 mouse
…AACUCCACCUA… Gene sequence #3 fungus
…GGUUGCACCGG… Gene sequence #4 amoeba
1. Compare the 4 gene sequences given above. Which 2 sequences are most closely related?
How can you tell?
E P I D E M I C
Laboratory Training for Field Epidemiologists
A L E R T
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2. How are all of the organisms similar? How are they different?
3. In summary, what can you say about the function of DNA with regard to Model 1?
MODEL 2:
Read This:
DNA is made up of bits of information called genes. These genes create specific “blueprints” for
building individual living things. Genes encode the information to make proteins such as eye color.
Proteins are made up of different combinations of Amino Acids.
4. Looking at model 2, where is DNA located within the cell?
5. Is the DNA molecule ever pictured out in the cytoplasm?
6. If DNA contains the instructions for making proteins, how must the instructions get out into
the cytoplasm? Describe what takes place for this to happen.
7. Explain how the proteins are made from the set of instructions. What are the molecules
involved in this process?
Read This:
DNA is contained within the nucleus of almost every cell in the human body (Red Blood Cells
excluded). The length of the DNA molecule is about 100,000 times as long as the cell itself, yet it fits
neatly inside of each nucleus. DNA will coil up tightly during cell division in order to move the
chromosomes easily into each new cell. When not dividing, the DNA remains condensed (called
chromatin), but not super-coiled so that protein synthesis and DNA replication can occur more easily.
MODEL 3:
Double Helix
Histone Proteins
Chromosome
Extended Chromosome
8. Describe the basic structure of the “Double Helix.”
9. How does the double helix condense down to fit into the nucleus?
10. When does the DNA supercoil into chromosomes and why?
MODEL 4:
11. How many chromosomes to humans have?
12. Describe how the chromosomes in the karyotype pictured
are arranged.
13. The last pair of chromosomes are not numbered. What
type of chromosomes do you believe these to be?
14. Is this a male or female karyotype?
The first 22 chromosomes are called “Autosomes”
which are the chromosomes that make us all human.
The last pair are the “sex chromosomes”. Males are
XY and females are XX.
15. When are these chromosomes most visible during the cell
cycle?
Read This!
In order to extract chromosomal DNA from human cheek cells, a sample of intact cells must first
be collected. In order to obtain them intact, a rinse must be used to help wash off and preserve cells in
solution. Pure water will not work because of the osmotic difference between the water and cells. An
isotonic solution must be used.
MODEL 5:
Hydro-philic
-phobic
water
loving
fearing
16. What might be a good isotonic solution to use for rinsing cheek cells out of our mouths? Why
can’t we just use water?
17. The above model is a diagram that represents the cell membrane and nuclear membrane. Describe
this barrier.
18. What type of molecules are the “hydrophobic” parts?
19. Given the above answer, what type of agent is useful in breaking down fats and oils? Think about
how you might remove these substances from your hands after eating greasy fried chicken.
Read This!
The breaking apart of the cell membrane is called cell lysis. Once the cell has been lysed (broken open),
the cell contents spill out forming a soup called: lysate. Ice cold ethanol when added to the lysate will
cause the DNA from the cells to precipitate out of the solution.
20. Once the DNA is extracted from the cells, what could it be used for? List some possibilities below.