Unformatted text preview: Part 1 - Simulating how Gene Expression works
1. Google “phet gene machine”. Open the flash program. Click on the “Lactose Transport” tab on
the top of the simulation.
2. On the screen you should see two floating blue molecules, these are RNA polymerase. There is also
an incomplete DNA gene beneath them. You can turn on the legend in the lower right and that will
help you identify the molecules. Click the “show legend” box in the lower right. 3. Drag the lac promoter into place. What happens to the RNA polymerase? Are any new molecules
The RNA polymerase became attracted to the lac promoter and at first it looked like they were bonding then the
RNA polymerase were in a way gliding along the bottom and now are just hovering over the lac promoter. No new
molecules created. 4. Drag the lacZ gene into place. What happens? What molecule is represented by the black line?
What is the name of the process that converts the lacZ DNA gene to the black line? As the RNA polymerase goes over the lacZ gene a black line appears representing messenger RNA. The process that
converts the lacZ DNA gene into a black line is called transcription. 5. Eventually, arrows appear from the black line and purple circles appear from it. What type of
molecules do the purple spheres represent? What is the name of the process that converts the black
line to the purple spheres?
The messenger RNA then turned into a LacZ molecule and doubled. This process is called translation, when RNA
converts to a protein. 6. Turn the lactose injector onto “Auto” mode. What happens to the lactose? Can it enter the cell?
It gathers outside the cell it cannot enter. 7. Drag the lacY gene into place. What happens to the lacY protein? What is the role of the lacY
LacY protein attaches to the cell membrane and then is used as a transporter through the cell membrane for the
lactose. 8. Now that lacY is letting lactose into the cell, we can see the function of lacZ. What happens to the
lactose once it is inside of the cell? What is the function of lacZ?
The lactose bonds to the lacZ proteins cutting the lactose in half making disaccharides turn into monosaccharides.
The monosaccharides then disappear showing they go into cellular respiration. Part 2 - Simulating how Gene Expression can be turned off and on
9. Drag the lac operator into place. Does anything happen because of it?
No, nothing changes. 10. Switch the lactose injector to “Manual” mode and wait for all lactose to disappear. Drag the lacI
promoter into place. Can the RNA polymerase bind both promoters? Is the RNA polymerase able to
make the lacI gene now?
Yes the RNA polymerase can bind to both promoters but we haven't attached the lacl gene yet so we are not certain
if it can make either the messenger RNA or the protein for lacl. 11. Drag the lacI gene into place. Does this allow for the creation of new proteins? To what does the
lacI protein bind to? What effect does the lacI gene have on transcription of the LacZ and LacY
lacl proteins are created, then one binds to the lac operator making it a repressor. The repressor that's also the lacl
protein then stops the RNA polymerase in reading either the LacZ or LacY genes not allowing them to make
messenger DNA or proteins. 12. Remove the lac operator. Wait for LacY to return to the membrane. Turn the lactose injector onto
“Auto” mode and wait for lactose to enter the cell. Drag the lac operator back into place. What
happens now to the LacI protein? Does the presence of lactose in the cell alter its ability to repress
translation? Without the lac operator the lactose binds with lacl proteins when dragging the lac operator it its spot the lacl proteins
begun to to bind with it but that didn't stop the lactose. The lactose would bind with lacl proteins that had already
binded with the lac operator and make the proteins detach from the operator. Yes the lactose in the cell does alter the
proteins ability to repress translation. 13. If the lacZ protein breaks down lactose, is it worthwhile to make it when there is no lactose around?
How does the bacteria use this system to efficiently control the production of the lacZ protein?
No it would be a waste of energy to male the lacZ protein with no lactose around. The system as a whole has in a
way an on and off switch so to be efficient as possible the lacZ protein along with the rest are only produced with a
presence of lactose. ...
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