Thinking Like a Scientist Activity 6
The greatest discoveries have come from people who have looked
at a standard situation and seen it differently.
Let's Get Together
Students will experience the importance of scientific collaboration and
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.
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.
For each group:
Duplicate the handouts to distribute to students.
- 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.
- 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.
- 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.
- 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.
- Describe the process you used to create and reproduce recombinant DNA.
- 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?
- 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