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Questions and Answers
What effect does ultraviolet light have on DNA?
What effect does ultraviolet light have on DNA?
Which enzyme is responsible for removing damaged DNA following ultraviolet exposure?
Which enzyme is responsible for removing damaged DNA following ultraviolet exposure?
What role does DNA polymerase play in the repair process after UV damage?
What role does DNA polymerase play in the repair process after UV damage?
What is an auxtotroph?
What is an auxtotroph?
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Which process is NOT associated with positive selection in identifying mutants?
Which process is NOT associated with positive selection in identifying mutants?
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How does replica plating assist in identifying mutants?
How does replica plating assist in identifying mutants?
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What happens after DNA repair by ligase following UV damage?
What happens after DNA repair by ligase following UV damage?
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What type of selection helps identify mutants that fail to perform a specific function?
What type of selection helps identify mutants that fail to perform a specific function?
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What is the default position of a repressible gene?
What is the default position of a repressible gene?
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Which of the following acts as an inducer for the lac operon?
Which of the following acts as an inducer for the lac operon?
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In the operon model, what is the function of the operator?
In the operon model, what is the function of the operator?
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What happens to the repressor when allolactose binds to it?
What happens to the repressor when allolactose binds to it?
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In an inducible operon, what is required for the structural genes to transcribe?
In an inducible operon, what is required for the structural genes to transcribe?
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Which of the following describes constitutive genes?
Which of the following describes constitutive genes?
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What is the role of the promoter in the operon model?
What is the role of the promoter in the operon model?
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Which of the following is true about catabolite repression?
Which of the following is true about catabolite repression?
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What role does the product of the regulatory gene (I) play in the operon system?
What role does the product of the regulatory gene (I) play in the operon system?
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What happens when allolactose binds to the repressor protein?
What happens when allolactose binds to the repressor protein?
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What is the function of cyclic AMP (cAMP) in the context of positive regulation?
What is the function of cyclic AMP (cAMP) in the context of positive regulation?
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What effect does catabolite repression have on bacterial metabolism?
What effect does catabolite repression have on bacterial metabolism?
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During the process of lactose catabolism, which enzymes are produced?
During the process of lactose catabolism, which enzymes are produced?
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Which statement accurately describes the activity of the repressor protein?
Which statement accurately describes the activity of the repressor protein?
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How does glucose availability affect cAMP levels in bacteria?
How does glucose availability affect cAMP levels in bacteria?
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What is the consequence of an inactive repressor in the operon?
What is the consequence of an inactive repressor in the operon?
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What is the significance of a colony that grows on medium with histidine but not on medium without histidine?
What is the significance of a colony that grows on medium with histidine but not on medium without histidine?
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What is the purpose of the Ames test in mutagenic studies?
What is the purpose of the Ames test in mutagenic studies?
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Which substance is added to the Ames test in order to facilitate mutagenic activity?
Which substance is added to the Ames test in order to facilitate mutagenic activity?
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In the context of the Ames test, what does a higher reversion rate indicate?
In the context of the Ames test, what does a higher reversion rate indicate?
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What type of mutation does the histidine auxotroph of Salmonella undergo to revert to his+ in the Ames test?
What type of mutation does the histidine auxotroph of Salmonella undergo to revert to his+ in the Ames test?
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What is the primary purpose of the Ames Reverse Gene Mutation Test?
What is the primary purpose of the Ames Reverse Gene Mutation Test?
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Which component is added only to the experimental sample in the Ames Test?
Which component is added only to the experimental sample in the Ames Test?
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What role does rat liver extract play in the Ames Test?
What role does rat liver extract play in the Ames Test?
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What outcome indicates a successful mutagenesis in the experimental plates?
What outcome indicates a successful mutagenesis in the experimental plates?
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After incubation, what type of bacteria colonies are counted on the plates?
After incubation, what type of bacteria colonies are counted on the plates?
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What might the control plate show due to natural occurrences?
What might the control plate show due to natural occurrences?
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What condition are the plates incubated at during the Ames Test?
What condition are the plates incubated at during the Ames Test?
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Why is the media used in the Ames Test specific to lacking histidine?
Why is the media used in the Ames Test specific to lacking histidine?
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Study Notes
Regulation of Bacterial Gene Expression
- Constitutive genes are expressed at a fixed rate, while other genes are expressed only when needed. This includes inducible, repressible and catabolite repression genes.
- Repression inhibits gene expression and decreases enzyme synthesis. Repressors are proteins that block transcription and repressible genes are "on" by default.
- Induction turns on gene expression with an inducer and inducible genes are "off" by default.
The Operon Model of Gene Expression
- An operon is a set of operator and promoter sites and the structural genes they control.
- The promoter segment of DNA initiates transcription of structural genes through RNA polymerase.
- The operator segment controls the transcription of structural genes.
The Operon Model of Gene Expression - Inducible Operon
- Structural genes are not transcribed unless an inducer is present in an inducible operon.
- The lac operon, found in E. coli, is an example of an inducible operon.
- The lac operon encodes three enzymes needed to metabolize lactose and is organized with adjacent structural genes (Z, Y and A) for these enzymes.
- The control region includes the promoter, where transcription begins, and the operator, which acts as a "stop or go" signal.
The Operon Model of Gene Expression - Repressible Operon
- The repressor protein (product of the I gene) binds to the operator, preventing transcription in the absence of lactose.
- In the presence of lactose, allolactose binds to the repressor protein.
- The inducer allolactose, a metabolite of lactose, binds to the repressor and allows transcription to occur.
Positive Regulation
- Catabolite repression stops cells from using carbon sources other than glucose.
- cAMP builds up when glucose isn't available.
- The catabolic activator protein (CAP) binds to cAMP and to the promoter, initiating transcription, allowing the cell to use lactose.
Identifying Mutants
- Positive, or direct, selection can identify mutant cells that grow differently from unmutated cells.
- Negative, or indirect, selection can detect cells unable to grow or perform a specific function.
- An auxotroph is a mutant with a nutritional requirement not present in the parent.
- Replica plating can be used to identify auxtotrophs.
Identifying Chemical Carcinogens
- Many mutagens are carcinogens (cause cancer).
- The Ames test uses mutant bacteria as carcinogen indicators to measure the rate of mutation reversal.
- The Ames test uses a histidine (his-) auxotroph of Salmonella to measure reversion to his+ after exposure to a mutagen.
- Rat liver extract is added to provide activation enzymes, so animal enzymes can facilitate mutagenic activity.
- Reversion rate indicates the degree to which a substance is mutagenic.
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Description
Explore the intricate mechanisms of how bacterial gene expression is regulated, focusing on constitutive, inducible, and repressible genes. Delve into the operon model, including the roles of promoters and operators in transcription control. Use this quiz to test your understanding of these fundamental concepts in microbiology.
