TITLE: The Amazing DNA
AUTHOR: Ryan Odom
GRADE LEVEL: 9th
CONCEPTS:
OBJECTIVES: The
students will be able to:
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Extract DNA from a thymus
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See nucleuses underneath the microscope
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Learn the basics of DNA, its components, and replication
TEKS:
¤112.43. Biology.
(c) Knowledge and skills.
(6) Science concepts. The student knows the
structures and functions of nucleic acids in the mechanisms of genetics. The
student is expected to:
(A) describe components of deoxyribonucleic
acid (DNA), and illustrate how information for specifying the traits of an
organism is carried in the DNA;
(B) explain replication, transcription, and
translation using models of DNA and ribonucleic acid (RNA);
MATERIALS LIST AND ADVACED PREPARATIONS:
Materials/Group
- Calf Thymus (also called
sweetbreads) may be cut into pieces and frozen for future use.
- Isotonic sucrose solution (
106.1 grams table sugar in 1 liter of water )
- Blender
- Cheese cloth
- Funnel
- Detergent solution ( 100 mL
dishwashing liquid [ I've used Dawn], 15 grams NaCl [table salt works
fine]: add distilled water to make a final volume of 1000 mL) ethanol
(95%) dispensed into 3-5 mL amounts into screw top test tubes or small
containers and stored in a freezer.
One container per student group.
2 test tubes per student group
- inoculating loops or thin
wires bent to form loop at the end for drawing up DNA from test tube
As much as possible, you would like to work with cold
materials and solutions. When the alcohol is removed from the freezer it should
be carried on ice into the classroom.
ENGAGEMENT:
DNA VIDEO
EXPLORATION:
Students are going to extract DNA from a Thymus. This
will allow them to realize there is something more going on inside the cell.
Procedure
- To break open the thymus
cells: Add a small piece of thymus (slightly smaller than an egg) to the
blender with enough sucrose solution to make a thin milkshake consistancy.
Blend until thymus is broken up. Kids think this is cool and gross to
watch!
- Pour the blended thymus
through a funnel which is lined with four thicknesses of cheese cloth. The
filtrate collected below the funnel will contain many nuclei which can be
observed under the microscope. This step removes gristle and other stuff.
- Pour about 2 mL of the nuclei
suspension collected from step 2 into a clean test tube for each student
group.
- Pour about 2 mL of detergent
solution into another clean test tube for each group.
- Students pour detergent
solution into test tube of nuclei suspension and gently shake tube from
side to side to mix. Do not shake enough to get foamy! In this step the
detergent will break open the lipid membrane of the nuclei and release
DNA. The salt in the solution will help neutralize the negative charges on
the DNA molecules so they will precipitate.
- Slowly pour COLD ethanol down
the inside of the test tube containing the nuclei/detergent mixture so
that a layer of ethanol forms on top of the mixture. DNA will come out of
solution at the place where the two layers meet.
- Use clean wires to dip into
layer where the two solutions meet and stir gently. Students will be able
to lift out masses of DNA. I have had students pull gently until they
lifted about 2 meters of long chain molecules out.
EXPLANATION:
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What did you think the white stuff is?
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Any ideas why we added the detergent?
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Why did we add salt to solution?
ELABORATING:
4 Minutes Introduce basic DNA structure Asks questions about topic
3 Minutes Introduce the components of DNA
1 Minute Give overview of DNA replication Open notebooks and
take notes
---------- Start overhead projector ---------------------------
4 Minutes Discuss semi-conservative replication Take notes and ask questions
3 Minutes Discuss how DNA unwinds Take notes and ask questions
2 Minutes Show model of unwinding DNA Take notes and ask questions
3 Minutes discuss how DNA replicates
EVALUATION:
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Application of material in their overall project.