Download DNA Extraction Lab

SBI 4U
Mrs. Holterman
Name: ________________________
Date: ________________________
DNA Extraction Lab
Pre-Lab Questions
Read through the rest of the lab to answer the following questions before the
lab.
1. Why does the plant tissue (strawberry) have to be heated, but the
animal tissue (liver) does not?
2. What are you accomplishing at the cellular level when you:
a. Blend the sample?
b. Heat the sample?
c. Add meat tenderizer (cleaving enzymes)?
d. Add detergent?
e. Add alcohol?
f. Add salt?
3. Why can’t you shake the test tube in step 1?
4. Answer the question in the purpose and give some explanation.
5. Create an observation table.
Introduction
In this investigation, you will isolate DNA from strawberries and liver. DNA is
100 000 times longer than the cell itself, but only takes up about 10% of the
space in the cell. It achieves this by tight folding and packaging with
proteins. DNA extraction is the first step in many biotechnological
procedures. Cell walls and cell membranes must be disrupted to isolate DNA,
using a kitchen blender before the experiment begins. Dish detergent will
dissolve the phospholipids in a process called cell lysis. Heat, detergents,
salts and cleaving enzymes will be used to further minimize contamination.
Purpose
Which type of cell has more DNA: plants (strawberries) or animals (liver)?
Method
Part 1:
1. Add 7mL of the detergent to a small test tube. Then, add 7 mL of the
liquefied strawberries to the detergent. Use a rubber stopper to seal
the test tube. DO NOT SHAKE!! Mix by slowly turning the test tube up
side down.
2. Place the test tube in a 65C water bath for 15 minutes to denature
the proteins. (While waiting, begin part 2).
3. Add 7 mL of meat tenderizer solution and swirl to mix. Meat tenderizer
is full of protease enzymes.
4. Use a funnel to secure a filter paper in the large test tube. Wet the
filter paper with water. Slowly pour the strawberry mixture into the
SBI 4U
Mrs. Holterman
5.
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8.
Name: ________________________
Date: ________________________
filter. Let the clear filtrate drip into the test tube (this might take 10
minutes).
Hold the test tube at a slight angle and pour in a matching volume of
ice cold ethanol on top of the filtrate using a pipette and letting it run
down the side of the tube. ** Don’t let it splash! **
Since DNA is insoluble in cold alcohol, it should appear at the interface
of the detergent and the alcohol, as a cloud of fine threads. Take
observations of this DNA.
If your DNA is not precipitating out of the ethanol, add a pinch of salt.
If you want to remove the DNA from the solution, use a wooden splint
to spool the DNA onto it by gently twisting the stick. Be careful not to
mix the layers.
Part 2:
1. Obtain a piece of liver and cut it into small pieces.
2. Place the pieces into the mortar, along with 10 mL of 0.9% NaCl
solution. Add a pinch of sand into the mixture to act as an abrasive,
and grind the tissue thoroughly for approximately 5 minutes.
3. Place a filter paper into a funnel sitting on a test tube. Pour the
remains of the liver and its liquid into the filter paper. Let the filtrate
drip into the test tube. This might take 10 minutes.
4. Add 3 mL of detergent to the test tube. Mix well (but DO NOT shake!)
for 30s.
5. Hold the test tube at a slight angle and pour in a matching volume of
ice cold ethanol on top of the filtrate using a pipette and letting it run
down the side of the tube. ** Don’t let it splash! **
6. The DNA should appear at the interface of the detergent and the
alcohol.
7. If your DNA is not precipitating out of the alcohol, add a pinch of salt.
Analysis
A) Look at your description of the DNA that you extracted. If DNA is a
rigid structure, why do the strands appear flexible? What features of
DNA’s structure account for its rigidity?
B) What chemical properties of DNA does this lab make use of?
C) Compare the amount of DNA extracted from the plant to the amount
from the liver. Is this what you expected? Why or why not?
D) Identify the areas of the procedure that may have lead to an incorrect
answer to the purpose. How could you change the procedure to get a
more accurate answer?