Control of Gene Expression in Prokaryotes
Houses usually have a light source in every room, but it would be a waste of energy to leave every light on all the time, so there are switches to turn off the lights in rooms that are not in use. Sometimes one switch controls several lights in the same room. Likewise, prokaryotic cells can turn genes on and off based on environmental factors. Sometimes related genes are grouped together with one switch. This group of genes, along with the sections of DNA that regulate them, is called an operon.
1.What type of operon is illustrated? An inducible operon
2.Consider the operon. Other than the gene that regulates the operon, how many genes are contained within the operon? Three
3.Where on the DNA strand does RNA polymerase bind to start transcription, the promoter, the operator or the terminator? The RN polymerase binds to the promoter
4.Which direction is the RNA polymerase moving? From the 3’ end to the 5’ end (Left to Right)
5.In which diagram is transcription and translation occurring successfully, diagram A or diagram B? Justifyyour answer with evidence. Transcription is occurring in diagram B because it shows mRNA and proteins being made from DNA.
6.Consider the non-science meaning of the following terms. Match the purpose with each of these sections in the operon in terms of gene transcription.
?Promoter oSpot where transcription begins
?Operator oSpot where transcription begins
?Terminator oOn/Off switch
7.Refer to diagram A.
a.What protein does the regulatory gene produce? A repressor protein
b.To what section of the operon does this protein bind? The repressor protein binds to the operator site.
c.Propose an explanation for why transcription is not occurring in diagram A. The repressor protein is blocking the RNA polymerase, therefore transcription cannot occur.
8.Refer to Diagram B.
a.When an inducer molecule attaches to the repressor protein, what happens to the repressor protein? The repressor protein changes shape
b.How does the change identified in part a allow transcription of the genes in the operon to occur? The repressor protein is no longer binding to the operator. Because of this, transcription
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