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DNA Replication

By Rachel Hughes and Kirstin Bittel



Time: 1 class period
Preparation Time: 5 minutes copying DNA stands
5 minutes setting up computer video feed
Materials: Computer with Internet access
DNA Model Overhead
DNA Cards
Licorice
Marshmallows (multicolored)
Toothpicks


Abstract
During this lesson students will model DNA replication using edible materials.
Purpose – Engagement of students in the modeling and replication of DNA.

Objectives
Students will be able to:-
1. Construct a 3-D model of DNA
2. Demonstrate an understanding of base pairs in written work and in a model.

National Science Education Standards
Content Area C – The Molecular Basis Of Heredity
- In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular "letters") and replicated (by a templating mechanism). Each DNA molecule in a cell forms a single chromosome.


Teacher Background
DNA is nucleic acid in the form of a double helix. It contains 4 bases that code for creation of proteins. The bases are A (adenine), G (guanine), C (cytosine), and T (thymine). A always pairs with T and C always pairs with G.


Related & Resource Websites

http://www.ncc.gmu.edu/dna/repanim.htm

 

 

Activity
Engagement (So, just what does DNA look like and how does it copy itself?)
1. Ask students to think back on their previous biology classes. Tell them, “We have spent a lot of time talking about DNA, but what does DNA look like? Why does DNA have this specific structure?”
2. Show students the computer simulation of DNA replication at
http://www.ncc.gmu.edu/dna/repanim.htm Draw students’ attention to the way DNA splits down the center when it is preparing to replicate. Note how the leading and trailing edge copy from different directions.
3. Tell students that they will be replicating a segment of DNA using licorice, toothpicks, and colored marshmallows. What will the licorice (sugar-phosphate backbone), toothpicks (hydrogen bonds), and marshmallows (nucleotide bases) represent? (Don’t be surprised if these are new terms to many of your students.)
4. Pass out DNA cards to groups of students. Once they receive their 10-letter DNA strand, they need to build the strand out of licorice, toothpicks and marshmallows. They have the leading edge, which is read left to right. (The overhead shows an example.)
5. Once students have successfully constructed their model, have them coil their DNA model. It will curl into a 1 _ circle. Discuss how this helps DNA be stored more easily.
6. Next, use scissors to cut the hydrogen bonds. They should begin their cut at the start codon (ATG) and end at the stop codon (TAG). Remind students that the DNA is read on the leading edge from left to right.
Once the DNA is separated, students should begin replicating the DNA starting with the leading edge. Their completed DNA molecule, with replication from start to stop codon, should look a bit like an open mouth.
7. Have students explain in their science notebook what each step in the modeling represents. Diagrams might be a helpful way to show steps if they are labeled.
8. Have students identify potential places for errors to occur either in discussion or notebooks. What do they think the consequences of these errors might be? (Do not answer or comment on these ideas as they will be discussed tomorrow)

Homework
Record concluding thoughts in their science notebooks.

Embedded Assessment

This is a great time to walk around the room and assess students on their ability to correctly match base pairs and whether students start their cut at the start codon and stop at the stop codon. (If there are two single strand segments on each end then it is done correctly)



PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:


an
NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award

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Supported by NIEHS grant # ES06694


1996-2007, The University of Arizona
Last update: November 10, 2009
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