10 Modeling bacterial transformation

By Shelley Casey

Provided by Kenan Fellows Program.

This lesson walks students through the process of bacterial transformation. It is ideal for classrooms that do not have the time or money for all students to complete a transformation; however, you can certainly follow up with the actual wet-lab. This lesson is recommended for basic biology classes and classes with diverse learners including those with learning difficulties rather than advanced biology classes.

Learning outcomes

Students will be able to describe the steps of bacterial transformation as well as give examples where this process may be useful.

Teacher planning

Time required

90 minutes

Materials needed

Per group of 2 students:

• 1 empty water bottle
• 2 feet of yarn
• 3 different colors of Velcro cut in 4 inch strips (each group needs 1 strip of each color)
• 1 sheet of small adhesive dots
• toothpicks
• plastic lacing
• 1 sandwich-size Ziploc bag
• 1 pair scissors
• 1 set of labels: ice, hot water, nutrient broth
• 1 sharpie
• 1 bottle of white-out

For teacher demonstration:

• hot plate
• Erlenmeyer flask
• balloon
• large beaker of ice water
• mitt for picking up hot flask

Technology resources

One computer with internet connectivity per pair of students and access to a printer is needed for this lesson. Animations may be shown to the class as a whole with the aid of a data projector or Averkey connection to the television. If students will be watching the animations in smaller groups, earphones are recommended.

Student handouts

Pre-activities

Students should already have knowledge of biotechnology terms such as PCR, restriction enzyme, clones, and sticky ends. They should also be familiar with cell organelles, structure of the plasma membrane, DNA structure and process of replication, and asexual reproduction.

Activities

1. Review biotechnology concepts such as restriction enzymes, sticky ends, and BAC cloning. Inform students that bacteria are used in biotechnology research to produce transgenic organisms.
2. Give each group of two students a copy of the lab sheet. Have one student read the opening paragraph aloud.
3. Direct students to look at the picture of the bacteria while you point out the different structures and review their functions.
4. Give each group the materials needed to build their models of bacteria. Be sure to point out what each item is meant to represent. It may be helpful to have a model that you have completed in advance to show the students what it will look like.
   • The empty water bottle represents the bacterial cell wall.
   • The yarn is the nucleoid DNA.
   • Small adhesive dots function as the ribosomes.
   • Toothpick are used as pili.
   • Plastic lacing represents flagella.
   • The Ziploc bag functions as the cell membrane.
5. Have a different student read the instructions for building the model aloud before students begin building. Students will use the following steps to build the bacteria model:
   1. Stick the adhesive dots at various places inside of the Ziploc bag. Place the yarn inside the bag as well.
   2. Punch a small hole in the bottom of the water bottle with the scissors. Tie a piece of plastic lacing to a toothpick and insert the toothpick into the hole you created (the toothpick in this case is just to keep your flagellum in place).
   3. Put the Ziploc bag inside of the water bottle and blow air into the bag to push it against the sides of the bottle. Poke several toothpicks into the sides of the bottle in random areas for the pili.
   4. Use the sharpie to draw negative signs (‐) on the surface of the bottle.
6. Once students have completed their bacterial models, explain that each different color of Velcro represents DNA from a different source: one from the bacteria itself, one for antibiotic resistance (either from that bacteria or another), and one from a completely different organism. This third type of DNA is the “DNA of interest” and it is what we want to see change in the bacteria. Remind students that in order for the DNA to have been cut, a restriction enzyme would have been used and in order to get the DNA to fit together, the cuts would have needed to produce sticky ends. Instruct students to put their Velcro pieces together to make a circle — this is their plasmid.
7. Explain that the plasmid and bacteria are now ready for transformation and show students the recombinant plasmid animation from the Harlem DNA Lab. It is not necessary to go through every animation on this site as it goes into detail for the specific glowing gene transformation lab. It does have lots of other great information if you would like your students to explore this later. It is used here as a preview of the process.
8. Distribute materials needed for transformation.
9. Have a student read Procedure 1 from the lab sheet and instruct students to follow the directions in bold type.
   1. Place the “Ice” label on the desk with the bacteria and plasmid, remove the cap from the bottle to represent the holes created.
   2. Take the white-out and cover up all of the negative charge symbols you drew on the water bottle.
10. Have a different student read the information under Procedure 2.
11. Perform the Balloon in the Flask demonstration as follows:

    Place 10 mL of water in a 250-mL Erlenmeyer flask. Bring the water to boiling. Remove the flask from the source of heat and quickly and carefully place an empty balloon over the mouth of the flask. (It helps to blow up the balloons once before they are used.) Place the flask with the balloon on it into a large beaker of ice water. As the flask cools, the pressure differential between the outside and inside of the flask will cause the balloon to invert and line the inside walls of the flask. This will show how heat-shock forces the DNA into the bacterial cell.

12. Now have students follow the directions in bold for Procedure 2.

    Replace the “Ice” label with the “Hot Water” label and push your plasmid into the Ziploc bag which is inside of the bottle.

13. Another student should read the information under Procedure 3 and then students can follow the directions in bold.

    Replace the “Hot Water” label with the “Ice” label and then add the “Nutrient Broth” label. Reseal the cap to the bottle.

14. Point out to students that the result of those three steps is a transformed bacterium. Read the final paragraph in this section and have students complete the concept check questions. You can either have students answer orally in a class discussion or spend some time writing the answers. Students will answer the following questions:
    • What are plasmids?
    • What is the function of restriction enzymes?
    • How can transformed bacteria that carry genes of interest be identified and isolated from the non-transformed bacteria?
    • Describe the steps involved in transforming a bacterial cell.
15. The final part of this lesson is to have students research applications of this technique. Have groups choose a topic from those provided on the list and use computers with internet connection to research their chosen topic. Allow a total of thirty minutes for instructions and research.
16. At the end of this time, allow each group to briefly describe what they found in their research. Groups waiting to tell about their topic should listen for similarities to their topic as well as how it may be different.

Assessment

Assess verbal and/or written responses to the concept check questions at the end of the lesson. Check for understanding that the plasmid that students created contained DNA from an organism other than a bacterium by asking them to draw and describe the plasmid on the board. Listen for misconceptions, and quickly correct, during the discussion of transformation applications.

Modifications

While this lesson can be presented to the entire class at once, students with hearing, sight, reading, or writing difficulties would benefit from being able to view the animations at their own pace. Working with another student also helps with organizing the discussion of findings for applications of transgenic organisms.

Alternative assessments

Written responses to the assessment questions could be accepted for those students who have speech disorders or anxiety due to verbal assessments.

Supplemental information

Upon completion of the creation of a transgenic American chestnut tree with fully functional blight resistant genes, trees could be released into the forest and given an opportunity to repopulate. This is the culminating step to the research being performed to restore the American chestnut.

Critical vocabulary

transformation

the genetic alteration of a cell resulting from the uptake, incorporation, and expression of DNA

plasmid

an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently, often circular and double-stranded

vector

a DNA molecule used as a vehicle to transfer foreign genetic material into another cell

competent

the ability of a cell to take up extracellular DNA from its environment

transgenic

organisms which have inserted DNA that originated in a different species

GMO

genetically modified organism, an organism whose genetic material has been altered using genetic engineering techniques.
Some GMOs do not contain DNA from other organisms, genes may just be removed or rearranged, and thus are not transgenic.

resistance

the capacity of an organism to defend itself against harmful environmental agents

conjugation

the transfer of genetic material between bacteria through direct cell-to-cell contact

transduction

the process by which DNA is transferred from one bacterium to another by a virus

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