Teaching Biotechnology With Models
Author: Paula Kelly
Woodrow Wilson Biology Institute
Any biology teacher who has surveyed her/his classes when beginning a section of cell biology is well aware of puzzled expressions. The mere suggestion of learning about something that cannot be seen on the desk top strikes fear in the minds of most students as well as their teachers! Teaching about biotechnology requires teaching about cells, chromosomes, genes and DNA. The use of models can ease that apprehension because they help our students visualize what they cannot see.
There are many sources for labs and activities dealing with models but some of the very best come from A Sourcebook of Biotechnology Activities, Rasmussen and Matheson project co-directors. This project was a collaborative effort between National Association of Biology Teachers and North Carolina Biotechnology Center. One activity from the sourcebook is summarized on the following pages. Additional information on this activity as well as on the Sourcebook itself can be obtained by writing:
National Association of Biology Teachers
11250 Roger Bacon Drive # 19
Reston, Virginia 22090
The Size Of The Genome
Rob Matheson and Carolyn Wynn
Target Age/Ability Group:
This can be adapted for a wide range of students from 7th grade life science to 12th grade AP biology.
Student/Class Time Required:
1 or 2 class periods and 1 homework
This activity uses scale models to very clearly represent the bacteria E. coli with all of its prokaryotic parts. Each lab group must have a supply envelope consisting of the following:
- A 2 cm (20mm) gelatin capsule-#0-can be purchased individually or in a box of many. (Pharmacy or health food store)
- 10 meters of two different colors of thread (try school colors)--each color represents a side of the DNA double helix ladder. It may be less confusing to place each color on a separate 3x5 card.
- A 4mm piece of yarn glued on a 3x5 card labeled"length of DNA in a single bacterial gene."
- A 10mm piece of different colored yarn glued in a circular manner to a 3x5 card labeled "bacterial plasmid."
Teacher Guide for Preparation of Materials:
The students are asked to read the background reading either before or after they have been divided into groups (4/group works well). The information on the reading page is very helpful in getting the students to relate the actual sizes to the models they will use. The authors use real life comparisons to help students visualize and compare actual sizes.
After the initial reading, the students are given Student Activity page 1. This will give them directions for putting together their bacteria.
- This activity needs to be carried out in a large area as students need to make a 10 m circle to illustrate chromosomal DNA.
- In the last step of the activity, they are asked to put both 10m strands in the capsule. At this point, it would be very helpful if you have discussed or demonstrated supercoiling. This will enable the students to see how the cell "achieves" this seemingly impossible task, as well as how they will achieve the same!
The activity concludes with a series of questions which may be used in part or in whole depending on the level of your students. The questions included in the Sourcebook addition are easily adapted to fit your needs.
THE SIZE OF THE GENOME
- After getting your envelope and groups, remove the gelatine capsule from the envelope. It represents a single E. coli bacterium that has been enlarged 10,000X.
- Remove the two 3" x 5" cards from the envelope. The lengths of yarn on the cards represent the lengths (and not the diameter) of an E. coli gene and plasmid magnified 10,000X.
- Remove and stretch out the two lengths of thread in the envelope. These represent the bacterial chromosome.
- Two people should make a circle with the two threads. This represents the bacterial chromosome which is simply a circle of DNA that is attached to the cell membrane.
- A third person now holds up the 3" x 5" card labeled "Length of DNA in a single bacterial gene" next to the DNA "loop." The 4 mm long piece of yarn glued on the card represents the length of a single gene. Remember, a gene is composed of all the segments of DNA that instruct the cell to make a single protein, whether these segments are continuous or not.
- With the light thread loop and the card labeled "Bacterial gene" still in view, ask the fourth person to hold up her/his 3" x 5" card labeled "Bacterial plasmid." The 10mm piece of yarn glued on this card represents a typical bacterial plasmid. Plasmids carry several genes necessary for their own replication and stability, but you can see that the plasmid is tiny in comparison with the bacterial chromosome. Plasmids can also carry genes that add important characteristics (such as antibiotic resistance) to a bacterium.
- Now that you have compared the sizes of the chromosomes, plasmids and genes, try to construct the bacterium. This means that the long lengths of thread representing the chromosome have to go inside the capsule. It's not easy!