Download Gene Expression (lac and trp operons)

Gene Expression (lac and trp operons)
1.) Complete the comparison of the lac Operon and trp Operons as a means of gene regulation in E. Coli
Lac Operon
Used for catabolic or
anabolic reactions?
Inducible or repressible?
Regulates production of:
Number of genes and how
they are controlled
What binds to the
operator/when does this
occur/inducer, repressor or
corepressor?
High levels of what
substance affects the
operon and how?
2. Why are genes under regulation?
3. What makes up an operon?
4. What is the function of the promoter ?
5. What is the function of the operator?
Trp Operon
6. What happens if lactose levels are low? Put the following list in order (1-5)
RNA polymerase is blocked from transcribing the genes for the lactose metabolizing enzymes
When RNA polymerase binds to the promoter, it cannot get past the LacI repressor protein, and the
transcription is blocked
The enzymes B-galactosidase, B-galactosidase permease and transacetylase are not required by the cell
These enzymes are involved in the metabolism of lactose, and their expression is under the regulation of the
lac operon.
Lacl, a repressor protein, is bound to the operator, which follows the promoter
7. What happens if lactose is present? Put the following list in order (1-4)
The three enzymes involved in the metabolism of lactose are transcribed and expressed.
The enzymes must be transcribed
Lactose binds to the Lacl repressor, changing Lacl’s shape and making it fall off the operator
Now that Lacl has been removed for the operator, RNA polymerase can proceed with transcription
8. What happens if tryptophan levels are high? Put the following list in order (1-3)
The trp repressor-tryptophan complex can now bind to the operator of the trp operon, blocking transcription
of the genes needed to synthesize tryptophan
The tryptophan does not need to be produced by the tryp operon
Tryptophan will bind to the repressor protein, changing its conformation
9. What happens if tryptophan levels are lowered? Put the following list in order (1-3)
The repressor protein changes shape without tryptophan and can no longer bind to the operator
There is not enough tryptophan available to bind to the repressor protein
RNA polymerase is able to transcribe the tryptophan synthesizing genes.
10. Label the following diagrams:
A. _____________________________________________
Lac Operon
B._______________________________________________
_
A.________________________________________________
B.
_________________________________________________________
Trp Operon