BIOLOGY 100 LAB PACKET LAB 5 – DNA Analysis
In this lab you will review the structural and functional properties of DNA. You
will also isolate strawberry DNA so you can observe it.
Image from the U. S. Department of Energy Human Genome Project
What is DNA:
DNA is a macromolecule made of nucleotides consisting of a phosphate, a sugar, and one of 4
different nitrogenous bases. DNA is essential for normal cellular function and it is found in all living
cells. Essentially, it contains the genetic recipe for making everything a living cell needs to survive. It
controls what a cell looks like and the specific functional capability of the cell. In Eukaryotic
organisms, DNA is normally found only within the cell nucleus in highly organized structures called
chromosomes.
Human, plant, and animal cells have lots of DNA stored in almost every cell in their body but that
DNA is not visible to the naked eye. In fact, that DNA is usually highly organized into efficient units
called chromosomes. However, we can use a very simple procedure to painlessly extract a visible
amount of DNA from most living cells.
Before you begin this lab, you will need to review the basic structural properties and the important
functional characteristics of DNA and chromosomes. Please go to the University of Utah, Learn
Genetics website. It contains a great tutorial titled Tour of the Basics. Completion of the tutorial will
help you better understand basic genetics and heredity. There are 6 segments in the tour of the
Basics series. You need to watch the first 3 but I suggest you watch all 6 because next week’s lab
will be about proteins and heredity.
Tour of the Basics Website: http://learn.genetics.utah.edu/content/begin/tour/
You will need to cut and paste the above address directly into your browser to access the site.
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BIOLOGY 100 LAB PACKET LAB 5 PROCEDURE
In this lab, you will isolate and observe DNA from a strawberry (or other soft fruit). When performing
the procedure, be sure to follow the protocol exactly as listed. Be aware of the time required for each
step You will use the information you have learned to answer the corresponding Lab 5 Homework
Sheet.
DNA extraction procedure listed below was obtained from the following source:
2003, Pioneer Hi‐Bred International, Inc. Page 4 of 11 Educational Services Program (ESP) Phone: 515‐270‐3364 or 3175 LAB 5 MATERIALS AND METHODS
Working together in groups of two, read through the entire procedure and follow the steps in
Parts I, II and III.
Materials:
Each pair of students should obtain 1 Lab box with the following contents:
• Zip-type, freezer bag (6”x 9”)
• 1 Coffee filter, cone-shaped, #2 size
• 1 Cup or beaker, 5 oz.
• Plastic pipette
Obtain the following items from your instructor:
• 1 Strawberry
• 10 milliliters DNA extraction buffer (soapy, salty water)
• 15 milliliters ice cold ethanol in test tube
Part I- Preparing the DNA extract
1. Have one partner get the lab box while the other partner gets the strawberry and
removes the stem and leaves.
2. Place one strawberry in a zipper bag.
3. Mash up the strawberry for 2 minutes.
4. Add 10 mLs of the extraction buffer to the bag.
5. Mash again for 1 minute. While one partner is mashing the other partner must do step
6.
6. Drape the coffee filter in the cup. Make sure the top part of the filter is folded over the
top of your cup and that the bottom of the filter does not touch the bottom of the cup.
7. Pour the mashed strawberries with the extraction buffer into the filter and let drip into
the bottom of the cup. This takes about 10 minutes.
Answer the Part I questions of your Lab 5 homework while you wait.
Part II: Pipette the strawberry extract into the alcohol
8. One partner gets a test tube that contains ice-cold ethanol.
9. Using a pipette, remove some of the strawberry extract from the cup. Carefully pipette
the strawberry extract into the alcohol in the test tube and watch the solution precipitate
(separate).
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BIOLOGY 100 LAB PACKET DO NOT SHAKE THE TUBE!!! Very gently, swirl the tube once or twice. Then let the tube
remain undisturbed.
Part III: Observations
10. Watch where the alcohol and extract layers come in contact with each other. Keep the
tube at eye level so you can see what is happening.
Answer the Part II and III questions in your Lab 5 homework sheet now.
NOTE ABOUT THE DNA YOU’VE EXTRACTED
DNA is a long, stringy molecule. The salt that you added in step one helps it stick together. So what
you see are clumps of tangled DNA molecules! DNA normally stays dissolved in water, but when
salty DNA comes in contact with alcohol it becomes un-dissolved. This is called precipitation. The
physical force of the DNA clumping together as it precipitates pulls more strands along with it as it
rises into the alcohol. You can use a wooden stick or a straw to collect the DNA. The image below
illustrates DNA that was successfully extracted from a strawberry. The DNA is the white, cloudy,
thread-like structure that is sitting on the surface of the strawberry juice. Your own DNA should look
similar (white, cloudy, threads suspended in the alcohol solution).
Image obtained from the following website: http://www.mysciencebox.org/DNAextraction 3|Page
BIOLOGY 100 LAB PACKET REAL-LIFE APPLICATIONS OF THE SCIENCE OF DNA EXTRACTION
Information below obtained from the University of Utah, Learn Genetics Website:
http://learn.genetics.utah.edu/content/labs/extraction/howto/faq.html
1. What can be done with extracted DNA?
This sample could be used for gel electrophoresis, for example, but all you will see is a smear. The
DNA you have extracted is genomic, meaning that you have the entire collection of DNA from each
cell. Unless you cut the DNA with restriction enzymes, it is too long and stringy to move through the
pores of the gel.
A scientist with a lab-purified sample of genomic DNA might also try to sequence it or use it to
perform a PCR reaction. But, your sample is likely not pure enough for these experiments to really
work.
2. How is DNA extraction useful to scientists? When do they use such a protocol, and why is it
important?
The extraction of DNA from a cell is often a first step for scientists who need to obtain and study a
gene. The total cell DNA is used as a pattern to make copies (called clones) of a particular gene.
These copies can then be separated away from the total cell DNA, and used to study the function of
that individual gene.
Once the gene has been studied, genomic DNA taken from a person might be used to diagnose him
or her with a genetic disease. Alternatively, genomic DNA might be used to mass produce a gene or
protein important for treating a disease. This last application requires techniques that are referred to
as recombinant DNA technology or genetic engineering.
3. Can I use a microscope to see the DNA that I extract?
Unfortunately, a microscope will not allow you to see the double helical structure of the DNA
molecule. You'll only see a massive mess of many, many DNA molecules clumped together. In fact,
the width of the DNA double helix is approximately one billionth of a meter! This is much too small to
see, even with the most powerful microscope. Instead, a technique called X-ray crystallography can
be used to produce a picture of the DNA molecule. It was by looking at such a picture (taken by
Rosalind Franklin) that James Watson and Francis Crick were able to figure out what the DNA
molecule looks like. See your textbook for more information about this.
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