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Terms in this set (15)
What is the Lac Operon?
an operon that is required for the transport and metabolism of lactose. Consits of three adjacent structural genes. transcription of this operon does not occur in the presence of glucose.
What are the structural genes in the Lac operon? and what do they code for?
LacY-codes for lactose permease, LacZ- codes for beta galactosidase, LacA-Galactoside transaceytlase
What happens when there is no lactose in the cell?
the lac repressor protein is active and binds to the lac operator site. Blocking RNA polymerase from transcription.
What happens when there is lactose in the cell?
when lactose enters the cell a small amount of it is converted into allolactose which binds to repressor causing a conformational change in the repressor and creating an inactive lac repressor. Thus preventing it from binding to the operator site. cAMP is present and able to bind to CAP which can bind to the binding site. Allowing RNA polymerase to bind to promoter and transcribes a polycistronic mRNA containing the Lacz, Lacy, and Laca genes.
converted from lactose via beta-galacosidase. Binds to repressor causing a conformational change in the repressor. INDUCER
What happens to the polycistronic mRNA? What does this allow the bacteria to do?
is translated to produce beta-galactosidase, lactose permease, and Galactoside transaceytlase proteins. Allows the bacterium to transport lactose into the cell and metabolize it.
Why is the lac operon important?
It allows for the digestion of lactose (if present) as a growth substrate if there is none of the preferred energy source glucose
Transcription of the lac operon is controlled by how many proteins, what kind of proteins, what are the proteins?
controlled by 2 regulatory proteins catabolite activator protein(cap) and the lac repressor protein
to bind to the activator binding site and facilitate transcription of lactose CAP has to first attach to cyclic AMP (cAMP)
Lac Repressor protein
binds to the operator site and blocks transcription
a second messenger. When glucose is present the concentration of cAMP in the cell is low.
What happens when glucose is present?
Low cAMP. which means that CAP cannot bind to the activator binding site. This means that RNA polymerase cannot transcribe. Lac operon off
What happens if there is no lactose in the medium?
the lac repressor binds to the operator site blocking transcription. Lac operon off
Explain what happens when both glucose and lactose are present
not enough cAMP to bind to CAP. therefore cannot bind to the activator binding site. Without the activator RNA Polymerase can not transcribe. At first Lac operon is off. Once all glucose is used then Lac operon is on
Explain what happens when neither glucose or lactose are present
High concentration of cAMP and CAP is bound to the activator binding site. RNA polymerase can bind to the promoter but is blocked by the repressor (because there is no lactose to bind and alter shape) no transcription
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