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Questions and Answers
What binds to the main repressor binding site of the lac operon?
What binds to the main repressor binding site of the lac operon?
Which molecule acts as the inducer in the lac operon?
Which molecule acts as the inducer in the lac operon?
What happens when the repressor binds to the operator?
What happens when the repressor binds to the operator?
How many possible binding sites does the repressor have on the lac operon?
How many possible binding sites does the repressor have on the lac operon?
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Which of the following processes is described as allosteric?
Which of the following processes is described as allosteric?
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Which gene encodes the lac repressor?
Which gene encodes the lac repressor?
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What enzyme is responsible for the uptake of lactose in E. coli?
What enzyme is responsible for the uptake of lactose in E. coli?
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Which of the following conditions induces the gene expression for lactose metabolism in E. coli?
Which of the following conditions induces the gene expression for lactose metabolism in E. coli?
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Which structural gene encodes β-galactosidase in the Lactose Operon?
Which structural gene encodes β-galactosidase in the Lactose Operon?
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What is the role of the repressor protein in the operon model?
What is the role of the repressor protein in the operon model?
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What molecule is produced by the action of β-galactosidase on lactose?
What molecule is produced by the action of β-galactosidase on lactose?
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Which of the following is NOT a structural gene in the Lactose Operon?
Which of the following is NOT a structural gene in the Lactose Operon?
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Study Notes
The Lactose Operon
- The lactose operon is a set of genes in bacteria that are regulated by the repressor protein.
- The operon consists of three structural genes: lacZ, lacY, and lacA.
- The genes are controlled by their own promoter (Plac) and an operator sequence.
Regulation of the Lactose Operon
- The lac repressor protein binds to the operator sequence, preventing transcription of the structural genes.
- There are three possible binding sites for the repressor: O1, O2, and O3.
- The repressor binds to O1 and either of the other two sites.
Induction of the Lactose Operon
- The inducer is allolactose, a minor reaction product of β-galactosidase.
- Allolactose binds to the repressor, causing it to be released from the operator, and transcription of the structural genes is turned on.
- Binding of the inducer to the repressor is allosteric, meaning it binds to a site other than the active site.
Lactose Metabolism in E. coli
- Lactose metabolism requires the activities of galactoside permease (uptake) and β-galactosidase (metabolism).
- β-galactosidase also catalyses the conversion of lactose to allolactose by transglycosylation.
- When glucose is abundant and lactose is lacking, cells produce low levels of enzymes for lactose metabolism.
- When lactose is present and glucose is absent, cells can use lactose as their energy source.
Induction of Genes for Lactose Utilization
- Gene expression is induced when glucose is absent and lactose is present.
- The graph shows the activity of enzymes involved in lactose utilization over time as lactose is added.
The Lactose Operon Genes
- lacZ: encodes β-galactosidase.
- lacY: encodes galactoside permease.
- lacA: encodes thiogalactoside transacetylase.
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Description
This quiz explores the regulation of the lactose operon in bacteria, including the role of the repressor protein and the negative control of structural genes.
