On Becoming a Scientist
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Thinking Like a Scientist Activity 6

The greatest discoveries have come from people who have looked at a standard situation and seen it differently.

--Ira Erwin

Let's Get Together



Objective

Students will experience the importance of scientific collaboration and communication.


About the Activity

New scientific knowledge is often based on scientists bringing information from different areas and putting it together in new ways. Many of today's discoveries have come about because scientists have pooled their efforts. The collaboration can be based on past research or on continuing investigations. The value of communicating and exchanging ideas is emphasized by the fact that scientists present their ideas at conferences, through papers in journals, and over computer networks.

In this activity, students will model the discovery of recombinant DNA technology to discover how collaboration can help create new knowledge.

Background Information

Two scientists, Herbert Boyer and Stanley Cohen, worked together to lay the groundwork for creating recombinant DNA technology. Boyer's research focused on how particular sequences of nucleotides could be cut from a strand of DNA using chemicals called restriction enzymes. These enzymes recognize short, specific nucleotide sequences in DNA molecules, and cut the bonds of the molecules at those sequences. The result is a set of double-stranded DNA fragments with single-stranded ends, called sticky-ends, that can be used to join DNA pieces originating from different sources.

Cohen's research focused on plasmids--small circular units of DNA that can carry genetic material from one bacterium to another. When a plasmid is taken up by a bacterial cell, the cell will reproduce using the new genetic information from the plasmid. Cohen discovered a method for introducing new plasmids into the bacteria. Working together, Boyer and Cohen discovered that they could modify plasmid DNA using restriction enzymes, and then introduce the plasmids into bacterial cells. As the bacteria reproduce, so does the recombinant plasmid. The result is a bacterial colony in which a modified plasmid containing a desired gene has been cloned.


Materials

For each group:


Preparation

Duplicate the handouts to distribute to students.


Instructions

  1. Divide the students into groups of four. Explain that two of each group will represent Science Team A, while the other half of each group will represent Science Team B. Choose one student in each team to be the Lab Technician, and one to be the Researcher. Distribute part A of Handouts 3 and 4 to the A subgroup, and part B of Handouts 3 and 4 to the B subgroup.
  2. Tell the students that they will use the information on the handouts to find a way to create and reproduce recombinant DNA. Explain that the Lab Technician in each group should prepare the DNA or plasmid strips as described on the handouts. Next, have the Lab Technicians compare the sequence of base pairs on an enzyme card with the sequences of the DNA or plasmid base pairs. If they find the same sequence of pairs on both the enzyme card and the DNA or plasmid strip, they should mark the location on the strip with a pencil, and write the enzyme name in the marked area. They should do this for each enzyme card.
  3. Once the Lab Technicians have identified all corresponding enzyme sequences on the plasmid, have the Team A Researchers identify those enzymes which make two cuts in the DNA, on either side of the shaded gene sequence. Have the Team B Researchers find those enzymes which cut the plasmid once and only once. They should discard any enzymes that cut the plasmid in the shaded plasmid replication sequence.
  4. Next, have the Researchers from both teams work together to identify the enzymes that make the appropriate cuts in both the DNA and the plasmid. Then ask the teams to work together to model a method for inserting a segment of DNA into the plasmid. Ask the combined teams to present their results to the class, as if they were presenting a paper at a conference.


Discussion Questions

  1. Describe the process you used to create and reproduce recombinant DNA.
  2. Was the information from both scientists necessary to model the process? Why or why not? How did the information about restriction enzymes help you? How did the information about plasmids help you?
  3. What was difficult about this process? What was easy? What did you enjoy most and least? Why?



Handout 3A: DNA and Restriction Enzyme Scenario

Handout 3B: Plasmid and Bacteria Scenario

Handout 4A: DNA and Enzyme Patterns

Handout 4B: Plasmid and Enzyme Patterns


Resource Book Index: On Becoming a Scientist


Winding Your Way Through DNA Resource Book Index


Winding Your Way Through DNA Lectures Index


About Biotech Index


 
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