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Regulation of Bacterial Gene Expression
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Regulation of Bacterial Gene Expression

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Questions and Answers

What effect does ultraviolet light have on DNA?

  • It creates single-strand breaks.
  • It decreases mutation rates.
  • It induces thymine dimers. (correct)
  • It enhances base pairing fidelity.

    • Which enzyme is responsible for removing damaged DNA following ultraviolet exposure?

  • RNA polymerase
  • Endonuclease (correct)
  • DNA ligase
  • DNA polymerase

    • What role does DNA polymerase play in the repair process after UV damage?

  • It removes thymine dimers.
  • It synthesizes new DNA. (correct)
  • It seals the DNA strands.
  • It cuts the damaged DNA.

    • What is an auxtotroph?

    <p>A mutant that requires additional nutrients.</p> Signup and view all the answers

    Which process is NOT associated with positive selection in identifying mutants?

    <p>Selection based on nutritional requirements.</p> Signup and view all the answers

    How does replica plating assist in identifying mutants?

    <p>By transferring colonies to assess growth variations.</p> Signup and view all the answers

    What happens after DNA repair by ligase following UV damage?

    <p>The old and new DNA strands are joined.</p> Signup and view all the answers

    What type of selection helps identify mutants that fail to perform a specific function?

    <p>Negative selection</p> Signup and view all the answers

    What is the default position of a repressible gene?

    <p>On</p> Signup and view all the answers

    Which of the following acts as an inducer for the lac operon?

    <p>Allolactose</p> Signup and view all the answers

    In the operon model, what is the function of the operator?

    <p>It stops or allows transcription.</p> Signup and view all the answers

    What happens to the repressor when allolactose binds to it?

    <p>It becomes inactive.</p> Signup and view all the answers

    In an inducible operon, what is required for the structural genes to transcribe?

    <p>Presence of an inducer</p> Signup and view all the answers

    Which of the following describes constitutive genes?

    <p>They are expressed at a fixed rate.</p> Signup and view all the answers

    What is the role of the promoter in the operon model?

    <p>To initiate transcription of structural genes.</p> Signup and view all the answers

    Which of the following is true about catabolite repression?

    <p>It inhibits the expression of other operons.</p> Signup and view all the answers

    What role does the product of the regulatory gene (I) play in the operon system?

    <p>It represses the operon by binding to the operator.</p> Signup and view all the answers

    What happens when allolactose binds to the repressor protein?

    <p>The repressor protein can no longer block transcription.</p> Signup and view all the answers

    What is the function of cyclic AMP (cAMP) in the context of positive regulation?

    <p>It binds to catabolic activator protein (CAP) to initiate transcription.</p> Signup and view all the answers

    What effect does catabolite repression have on bacterial metabolism?

    <p>It prevents the use of carbon sources other than glucose.</p> Signup and view all the answers

    During the process of lactose catabolism, which enzymes are produced?

    <p>Permease and β-Galactosidase.</p> Signup and view all the answers

    Which statement accurately describes the activity of the repressor protein?

    <p>It prevents transcription by binding to the operator when active.</p> Signup and view all the answers

    How does glucose availability affect cAMP levels in bacteria?

    <p>Glucose availability decreases cAMP levels.</p> Signup and view all the answers

    What is the consequence of an inactive repressor in the operon?

    <p>Transcription of structural genes is allowed.</p> Signup and view all the answers

    What is the significance of a colony that grows on medium with histidine but not on medium without histidine?

    <p>It shows the colony is a histidine-requiring mutant.</p> Signup and view all the answers

    What is the purpose of the Ames test in mutagenic studies?

    <p>To measure the rate of mutation reversal in bacteria.</p> Signup and view all the answers

    Which substance is added to the Ames test in order to facilitate mutagenic activity?

    <p>Rat liver extract.</p> Signup and view all the answers

    In the context of the Ames test, what does a higher reversion rate indicate?

    <p>A greater degree of mutagenicity of the substance.</p> Signup and view all the answers

    What type of mutation does the histidine auxotroph of Salmonella undergo to revert to his+ in the Ames test?

    <p>Point mutation.</p> Signup and view all the answers

    What is the primary purpose of the Ames Reverse Gene Mutation Test?

    <p>To determine if a substance is a mutagen</p> Signup and view all the answers

    Which component is added only to the experimental sample in the Ames Test?

    <p>Suspected mutagen</p> Signup and view all the answers

    What role does rat liver extract play in the Ames Test?

    <p>It serves as an activator for the suspected mutagen</p> Signup and view all the answers

    What outcome indicates a successful mutagenesis in the experimental plates?

    <p>A significant increase in histidine-synthesizing revertants</p> Signup and view all the answers

    After incubation, what type of bacteria colonies are counted on the plates?

    <p>Histidine-synthesizing revertant bacteria</p> Signup and view all the answers

    What might the control plate show due to natural occurrences?

    <p>Spontaneous histidine-synthesizing revertants</p> Signup and view all the answers

    What condition are the plates incubated at during the Ames Test?

    <p>37°C for 2 days</p> Signup and view all the answers

    Why is the media used in the Ames Test specific to lacking histidine?

    <p>To force dependent bacteria to revert to histidine synthesizers</p> Signup and view all the answers

    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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    Bacterial Gene Expression Regulation PDF

    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.

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