Download DNA extraction lesson plan

LESSON PLAN
Teacher: ______________________
Grade: ___9-12__ Date: _________
Objective/Purpose: to see and understand that DNA is contained in living organisms and to
extract DNA from bananas using a simple chemical procedure
Resources: What I need for class (e.g., transparencies, calculators, handouts, supplies):
Supply list:
1) A blender (regular kitchen blender is fine).
2) filters (cheese cloth or coffee filters) about 20cm squared per group of 4 students, and a few
back ups.
3) scissors to cut up the filters if not pre-cut into 20 cm squares.
4) one small test tube per student (or per group of students)
5) one stir rod per student (should fit well into the test tube)
6) two small beakers (50 or 100ml) per group of 4 students
7) about 40ml of liquid dish soap (not dishwasher, just plain dish detergent).
8) about 5tbl spoons of salt
9) two or three bananas (I've heard that kiwis or frozen peas also work).
10) about 100-200ml of 95% Ethanol.
11) a large jug/beaker/bottle for water.
*quantities of chemicals are enough for the whole lab
Other resources:
Overhead transparencies of diagrams of DNA.
Overhead of genetic code.
Hand outs of genetic decoding challenge activity.
Warm Up: Discussion of DNA,
Vocabulary: DNA
Q. Who has heard of DNA? Where have you heard about it?
Q. What is DNA? A. A long molecule found in every living cell. It provides the “code” or “blueprint” for making up entire organisms (from bacteria to people).
Q. What does it stand for? A. Deoxyribonucleic Acid
Q. Where is it found? A. In all living organisms (except a few types of viruses).
Q. Where is it found inside organisms? A. inside every cell, and more specifically in side the
nucleus of the cell.
Background: Students will have a varying background about DNA. Find out from teacher
ahead of time what the background is. Ask questions as in WarmUP.
Lesson Overview:
1) Start with questions and answers listed above in warmup. (2min)
2) Present diagram of DNA. Discuss the “twisted ladder” double helix shape of DNA.
(1min)
3) Lab.
a. Teacher Instructions: At front of class peel banana, put in blender and add about
2-3 cups of water. Blend banana well.
b. Explain: the blender breaks up the cells of a banana, releasing the contents.
c. Teacher Instructions: Hand out materials to each group. Each group should
have:
i. two beakers,
ii. one filter
iii. enough test tubes and stir rods for one per student. Can be modified to
have one test tube per group.
d. Go around with blended up banana and pour about 50-100ml of banana blend into
one beaker for each group.
e. Student Instructions (each groups should carry out):
i. Add about 1 ml of dish detergent to the banana mixture.
ii. Stir slowly for about 1 min, trying not to create bubbles.
iii. Add about two pinches of salt to the mixture.
iv. Stir again for about 1 min.
v. Place the filter over the second, clean beaker and make it dip down in the
middle so it forms a funnel type shape.
vi. Pour banana blend into filter. Allow it to filter through
vii. Transfer the filtrate to each of the test tubes, filling up to about 3 cm of the
bottom of the test tube.
f. Explain:
i. Q: what does the soap do? A. It breaks down cell membranes and
dissolves lipids. (Cell membranes are made from lipids). In other words,
the DNA is separated from the fats and membranes with this step.
ii. Q. what does the salt do? A. It precipitates out the proteins and
carbohydrates (sugars), making them fall to the bottom of the beaker. It
also makes DNA very sticky to itself.
iii. Q: what does the filter do? A. It removes many of the cellular debris,
allowing DNA to pass through. It keeps the precipitated proteins and
sugars from going through to the next step.
g. Teacher Instructions:
i. Go around and pour approximately an equal volume of ethanol into the
students’ test tubes. Instruct the students to stir very gently after. The
alcohol should form a distinct, clear layer on top of the banana mixture.
h. Explain:
i. the alcohol is much less dense than the rest of the material, and therefore
floats on the top. DNA is soluble in water, but not in alcohol, so it
precipitates out. The white fluffy looking material seen in the alcohol
layer is DNA. The salt has helped make it look white.
Assessment:
Students’ responses to questions asked of them in class can be used to gauge their understanding
throughout the lesson.
Homework:
NONE
Enrichment:
DNA decoding activity. If time allows do this activity (it takes up to 20 mins).
1) Explain that DNA is made up of simple parts, called nucleotides which make up the
“rungs” of the ladder. The sequence of these nucleotides is what is important in the code
of the DNA.
2) Explain the genetic code. The nucleotide sequence is read in groups of three. Each group
of three is called a “codon” and codes for a subunit of protein called amino acids. We
will be reading the codons in our activity and assigning them their amino acids.
3) How to read the genetic code. –Explain how to read the genetic code table.
4) Help students complete the DNA decoding challenge activity.
Remediation:
The explanation of what is happening at each step of DNA extraction can be simplified to say
that the chemicals added (salt, detergent) help to separate out the parts of the cell that we don’t
want (everything but the DNA) from the parts we do want (the DNA!). The alcohol then isolates
the part we do want – the DNA!
Evaluation:
NA