A length of DNA next to the structural genes. It can turn them on or off.
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What is the promoter region?
A length of DNA to which the enzyme RNA polymerase binds to begin transcription of structural genes Z and Y.
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What are the structural genes and what do they code for?
Z codes for the enzyme B-galactosidase and Y codes for the enzyme lactose permease. Consist of a sequence of base pairs that can be transcribed into a length of mRNA.
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Where is the regulatory gene (I) and what does it do?
It is not part of the operon. It codes for the repressor protein and blocks the promoter region.
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What else does the regulatory gene do?
It transcribes and translates to synthesise a repressor protein.
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What does the repressor protein do?
It binds to the operator region which blocks part of the promoter region, preventing RNA polymerase from binding
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What is the effect if the repressor protein is removed?
It will not block the promoter region and RNA polymerase will be able to bind.
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What does RNA polymerase do?
Binds with the promoter region.
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What is the role of B-galactosidase?
Catalyses the hydrolysis of lactose to glucose and galactose.
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What is the role of lactose permease?
Transports lactose into the cell.
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What is the first step when lactose is absent?
Regulator gene is transcribed and translated and the repressor protein is synthesised.
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What does the repressor protein have in terms of binding?
Has two binding sites. One that binds to lactose and one that binds to the operator region.
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What does the repressor protein bind to and what does this cause?
Repressor protein binds to the operator region and blocks part of the promoter region meaning RNA polymerase cannot bind to it.
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What happens now that RNA polymerase cannot bind to the promoter region?
The structural genes cannot be transcribed into mRNA.
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What does the absence of mRNA mean?
The genes cannot be translated and B-galactosidase and lactose permease cannot be synthesised.
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What is the first thing that happens in the presence of lactose?
Lactose can bind to the binding site on the repressor protein.
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What does this binding cause?
Causes the repressor protein to change shape so it cannot binding to the operator region. Repressor protein breaks away from the operator region.
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What effect does this have?
If the repressor protein cannot bind to the operator region, the promoter region will not be blocked so RNA polymerase will bind to the promoter region.
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What does the binding of RNA polymerase to the operator region cause?
Allows start of transcription and translation of the structural genes.
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What does the operator-repressor-inducer system act as and what does it allow?
Acts as a switch. Allows the transcription and translation of structural genes Z and Y into B-galactosidase and lactose permease.
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What can E.coli bacteria use?
Use the enzyme lactose permease to take up lactose from the medium into their cells.
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What is the effect of taking up lactose?
Lactose can be converted into glucose and galactose using enzyme B-galactosidase.
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