Gene Expression in Prokaryotes
The central dogma of molecular genetics can be described as the following: Gene –
mRNA – ribosome – tRNA – amino acids – protein. In short, genes are used to make
proteins. When an organism is actively using genes to make proteins it is called gene
expression.
The BioCoach Activity and Lac Operon animations in the “Genetic Engineering” section
of Unit 3 on the “biotech wiki” are intended to help the student understand one type of
mechanism bacteria use to control the genes that make proteins.
1. Go to the “Lac Operon Explanation and Animations” link. Read the first section.
Make a guess as to what kind of environmental signal can cause a gene to be
expressed in prokaryotes (bacteria).
2. Go to “Concept 1”. Study the paragraph and diagram. Can you figure out which
food source is used, in this case, to signal gene expression?
3. Go to “Concept 2”. Notice the structural genes are called “lac Z, lac Y and lac
A”. What does the “lac” connotation refer to?
4. As you study and read “Concept 2, Concept 3 and Concept 4”, open the additional
“Lac Operon Animation” from the wiki site. Watch and listen to the animation
here several times. Now, go back to the first animation site (BioCoach Activity).
What is the job of the purple, regulatory protein that binds to the operator region
of the lac operon?
5. Look at “Concept 5”. What would the blue/green RNA polymerase molecule be
doing if the regulatory protein was not present? What substance must be
present to remove the regulatory protein so that RNA polymerase can do its job?
6. Why is it beneficial for the bacterium to only make the structural genes when
lactose is present?
7. You may stop after reading “Concept 10”. Something to think about and then
answer: If you wanted to “trick” a bacterium into producing a different protein
from a newly introduced gene, where on the operon would you insert the gene?
8. What would you provide in the environment of the bacterium in order to get the
bacterium to “express” your newly introduced gene?