Transformation and Genetically Modified Foods (Mara Desso)

Author(s)

Mara Desso, Valencia High School

NGSS Engineering Standards

HS-ETS1-3.

Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.

Materials needed

scissors

tape, 3 small pieces

DNA Sequences for Cut-Outs, one per group; these represent plasmid DNA and mammal DNA containing the insulin gene; helpful to print page 1 on different colored paper than page 2

Restriction enzyme cut sites handout

Modeling Bacteria Transformation Worksheet, one per group

Assessment Questions, one per student

stapler (can be shared among groups)

Procedure

Guiding question: How can you design a method for inserting the insulin gene into a plasmid that can be used to transform bacteria in order to generate insulin protein?

    • With the Students

        1. Divide the class into groups of two students each. Hand out to each group a worksheet and its two strips of DNA sequences, pointing out which will be used to create the plasmid, and which is the mammal DNA containing the insulin gene.

        2. Direct groups to tape together the ends of the plasmid DNA to form a circular piece of DNA (see Figure 2) so that the printed sequence is visible on the outside of the plasmid. This is the initial plasmid that will be modified with the insulin gene.

A drawing that looks like a circular band with a piece of tape at its seam.

          1. Figure 2. Illustration of the circular DNA created in step 2.

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        1. Look at each of the restriction enzymes provided. Scan both the plasmid and the mammalian DNA to determine which restriction enzyme should be used to cut the insulin gene out of the mammalian DNA and place it into the plasmid DNA. MAKE SURE YOUR ENZYME CUTS THE INSULIN GENE OUT OF THE MAMMALIAN DNA AND DOES NOT CUT THE GENE APART!!!

        2. Once you have determined which enzyme will cut the DNA in the appropriate spots, find the recognition sites on both the plasmid and the mammal DNA. The restriction enzyme being used will search for a specific base pair sequence on the DNA to cut. This sequence and the cut pattern are shown in Figure 3. Have students look for this sequence on both DNA strands. Anywhere they find the full sequence is a recognition site; have them draw a dotted line at the site where the restriction enzyme will cut. Doing this usually prevents students from cutting straight across in the next step.

        3. Have students apply the restriction enzyme (represented by scissors in this model) to cut the DNA at the marked locations. Performed correctly, students make one cut through the plasmid and two cuts on the DNA containing the insulin gene. These cuts are made on either side of the designated gene. They are "staggered" cuts, forming the "sticky ends." Now that the desired gene is isolated, it is ready to be added to the plasmid DNA (see Figure 4).

A drawing shows a blue circular band, like Figure 2, but with a staggered cut/joint. A long red rectangle also has two of those same staggered cuts near each end, with its inner portion removed.

          1. Figure 4. In blue, the model plasmid after being cut by a restriction enzyme. In red, the mammal DNA with cuts and its isolated insulin gene with sticky ends.

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        1. Next, have students use the ligase enzyme (represented by tape in this model) to rebuild the plasmid with the new gene incorporated. If the DNA sequences have been correctly cut, the base pairs from each end of the gene match exactly with the cuts made in the plasmid. Tape the ends of the gene to the matching sticky end on the plasmid (see Figure 5).

A circular blue band with two staggered cuts that join together the original plasmid and the insulin gene into one loop.

          1. Figure 5. The final recombinant model plasmid, a merger of the original plasmid DNA and the added insulin gene.

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        1. If groups have correctly performed their genetic engineering simulations, expect them to now have circular recombinant plasmids that each contain the gene to produce insulin. Have them staple their recombinant models on their worksheets and complete the worksheets as a team.

        2. Conclude the activity by administering the Assessment Questions, as described in the Assessment section. Have students staple.

Procedure has been adapted from Teach Engineering.

Extension: You may consider having students simulate placing the plasmid into a bacterial cell and going through the process of transcribing the gene to make RNA and then translating it to make protein so that they fully comprehend the entire transformation process.

Questions

  • Post-activity assessment questions

  • What are the benefits of using genetic engineering to alter the DNA of organisms? List at least 3 examples of beneficial uses of genetic engineering.

  • What are the drawbacks of using genetic engineering to alter the DNA of organisms? List at least 3 examples of potentially harmful uses of genetic engineering.

  • Create an argument- should genetic engineering continue to be used to generate foods? Use evidence from your research to justify your claim.

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