Download Operon Models

AP BIOLOGY
ACTIVITY: BUILDING PROKARYOTIC OPERONS
Assignment For Table Groups 1-5:
Your Group of 3 will build a negative REPRESSIBLE operon (trp). Your model should include
representations the following elements:
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A constitutive Repressor Gene located “some distance” from your operon
A promoter region that allows the binding of RNA Polymerase
An Operator Region that allows the binding of the repressor protein
The Structural Genes that comprise the rest of the operon
A repressor Protein with an active AND an allosteric site
A small regulatory molecule capable of causing a conformational shape change in the
repressor protein
Instructions:
1. Using a serrated knife, cut an 8-inch segment from the noodle. This segment will be used as the
repressor protein.
2. Each end of the noodle/operon should feature an unlabeled/untaped section to show the
continuation of the DNA strand.
3. Wrap spirals of colored electrical tape (or shade the noodle with colored markers) where each of
the 5 gene domain regions would be found (trp E, trp D, trp C, trp B , and trp A), using a different
color for each gene domain.
4. Tape or shade in the regulatory gene (trp R) region as far upstream of the promoter region as
possible.
5. Using a permanent pen, draw the shape of the active form of the repressor protein onto the lower
portion of the noodle/operon, in the operator region. Make the shape simple since you will need to
carve it out using a serrated knife. Also, carve a matching shape into the regulatory repressor protein
piece that you cut off in step 1 above.
6. On the bottom side of the repressor protein, carve a U and wedge the tennis ball into the U.
7. Cut a piece of wire from a coat hanger and shove the wire into the repressor protein and bend the
repressor protein into a shape so that it will not fit the operator region if the co-repressor
(tryptophan) is not in place.
8. Write the word “tryptophan” on one of the tennis balls. Write “repressor protein” on the carved
foam piece. Now label the various parts of the noodle/operon using a permanent marker “trp R,”
“promoter/operator,” “trp E,” “trp D,” “trp C,” “trp B,” and “trp A.”
9. Place stick-on tabs on the parts of the operator and the repressor protein that fit together, so that
they can stick together without being held in place. You may do the same for the repressor and the
co-repressor/tryptophan ball.
Assignment For Table Groups 6-10:
Your group of 3 will build a functioning operon that is capable of demonstrating positive control (Lac
operon). Your model should include representations the following elements:
• A constitutive Repressor Gene located “some distance” from your operon
• A promoter region that allows the binding of RNA Polymerase
• An Operator Region that allows the binding of the repressor protein
• The Structural Genes that comprise the rest of the operon
• A repressor Protein with an active AND an allosteric site
• A small regulatory molecule capable of causing a conformational shape change in
the repressor protein
• CAP and CAP binding Site
Instructions:
1. Using a serrated knife, cut an 8-inch segment from the noodle. This will be used as the
repressor protein.
2. Again, each end of the noodle/operon should feature an unlabeled/untaped section, to show
the continuation of the DNA strand.
3. Wrap spirals of colored electrical tape (or shade the noodle with colored markers) where each
of the 3 gene domain regions would be found (lac Z, lac Y, and lac A), using a different color
for each gene domain.
4. Tape or shade in the regulatory gene (lac I) region, which is immediately upstream of the
promoter region.
5. Using a permanent pen draw the shape of the active form of the repressor protein onto the
lower portion of the noodle in the operator region. Make the shape simple, like the one in the
diagram, since you will need to carve it out using a serrated knife. Also, carve a matching
shape into the regulatory repressor protein piece that you cut off in step 1 above.
6. On the bottom side of the repressor protein, carve a wide, semicircle shape that is a little too
wide to accommodate the tennis ball. You want the repressor protein to have 2 shapes, one
that fits the operator shape perfectly when the inducer is NOT present and one that distorts
the repressor so that the carved top shape appears to pop out of the operator when the inducer
fits into the bottom (you can shove a piece of coat hanger wire into the repressor to make it
hold 2 different shapes).
7. Write “allolactose” on one of the tennis balls. Write “repressor protein” on the carved foam
piece. Write “lac I,” “promoter/operator,” “lac Z,” “lac Y,” and “lac A” at the appropriate
places along the noodle.
8. You may place stick-on tabs on both the operator and repressor protein parts so that they can
stick together without being held in place. You may do the same for the repressor and the corepressor/allolactose ball.
ALL TABLE GROUPS:
Once the Operon Models have been constructed, Table groups will pair up as follows:
1+6
2+7
3+8
4+9
5 +10
Each group needs to prepare and practice a short verbal presentation using the operon models your
group has built as a prop. Your presentation needs to be able to:
(a) explain how the operon works within the nutritional circumstances it is likely to find itself
(b) distinguish between Negative and Positive control
(c) distinguish between Inducible and Repressible operons.
Each group will receive a grade that is based on 3 criteria:
1. Accuracy of model
2. Thoroughness of explanation
3. Your table mate’s grades on a short quiz. (In other words, you will be grades on the success of
your students!)