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Operons in Prokaryotes Quiz
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Operons in Prokaryotes Quiz

Created by
@UnparalleledEcoArt

Questions and Answers

What type of operon is illustrated in Model 1?

  • Inducible operon (correct)
  • Repressible operon
  • Negative control operon
  • Positive control operon

    • Consider the operon in Model 1. Other than the gene that regulates the operon, how many genes are contained within the operon?

    Three

    In Model 1, where on the DNA strand does RNA polymerase bind to start transcription?

    The RNA polymerase binds to the promoter.

    Which direction is the RNA polymerase moving in Model 1?

    <p>Left to right (from 3' to 5' end)</p> Signup and view all the answers

    In which diagram of Model 1 is transcription and translation occurring successfully, diagram A or diagram B?

    <p>Diagram B</p> Signup and view all the answers

    Match the purpose with each of the sections in the operon in terms of gene transcription:

    <p>Promoter = Spot where transcription starts Operator = On/Off switch Terminator = Spot where transcription ends</p> Signup and view all the answers

    What protein does the regulatory gene in Model 1 produce?

    <p>A repressor protein</p> Signup and view all the answers

    To what section of the operon does the repressor protein bind?

    <p>The operator site.</p> Signup and view all the answers

    Propose an explanation for why transcription is not occurring in diagram A.

    <p>The repressor protein blocks RNA polymerase so transcription of genes X, Y, and Z cannot occur.</p> Signup and view all the answers

    When an inducer molecule attaches to the repressor protein, what happens to the repressor protein?

    <p>The repressor protein changes shape.</p> Signup and view all the answers

    How does the change in the repressor protein allow transcription of the genes in operon to occur?

    <p>The repressor protein no longer binds to the operator and is no longer blocking RNA polymerase.</p> Signup and view all the answers

    Explain what would happen within the lac operon when lactose levels are LOW.

    <p>Not enough allolactose is present. The repressor protein binds to the operator, not allowing transcription of the operon genes.</p> Signup and view all the answers

    Explain what would happen with the lac operon when lactose levels are HIGH.

    <p>When there are high levels of lactose present, the operon is switched 'on', producing proteins that break down lactose.</p> Signup and view all the answers

    In Model 2, where on the DNA strand does RNA polymerase bind to start transcription?

    <p>To the promoter.</p> Signup and view all the answers

    In which diagram of Model 2 is transcription and translation occurring successfully, diagram A or B?

    <p>Diagram A</p> Signup and view all the answers

    Does the regulatory gene in Model 2 produce a protein that is an active or inactive repressor naturally?

    <p>The regulatory gene produces a naturally inactive repressor protein.</p> Signup and view all the answers

    Describe the role of the corepressor molecule in the repressible operon system shown in Model 2.

    <p>The corepressor molecule activates the repressor protein and prevents the promoter from making proteins.</p> Signup and view all the answers

    What compound could serve as the corepressor of the TRP operon in E. coli?

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

    Compare and contrast an inducible operon and a repressible operon.

    <p>A repressible operon is naturally 'on' and can be repressed, while an inducible operon is usually 'off' but can be turned 'on'.</p> Signup and view all the answers

    Which type of operon, inducible or repressible, would an organism likely use to produce enzymes needed to metabolize a nutrient in its environment?

    <p>Repressible operon</p> Signup and view all the answers

    Which type of operon, inducible or repressible, would an organism likely use to produce enzymes needed from smaller molecules?

    <p>Inducible operon</p> Signup and view all the answers

    Propose an explanation for why operons evolved in prokaryotes.

    <p>Operons allow for coordinated expression of genes, optimizing energy use by producing all needed proteins simultaneously when required.</p> Signup and view all the answers

    In which diagram of Model 3 is transcription occurring successfully, A or B?

    <p>Diagram B.</p> Signup and view all the answers

    In Model 3, where on the DNA strand does RNA polymerase bind to start transcription?

    <p>To the promoter.</p> Signup and view all the answers

    Propose an explanation for why RNA polymerase is not bound to the promoter in diagram A of Model 3.

    <p>The RNA polymerase cannot initiate its functions unless the ligand tells the activator protein to attach to the promoter.</p> Signup and view all the answers

    What protein does the regulatory gene in Model 3 produce?

    <p>An activator protein.</p> Signup and view all the answers

    To what section of the operon does the activator protein bind?

    <p>The promoter.</p> Signup and view all the answers

    Can the protein produced by the regulatory gene in model 3 bind to the operon itself?

    <p>No, the activator protein needs a signal from the ligand to bind to the operon.</p> Signup and view all the answers

    Propose an explanation for why transcription is not occurring in diagram A but is occurring in diagram B.

    <p>In diagram B, the ligand is present and has delivered the message to activate the protein, while in diagram A the ligand is absent.</p> Signup and view all the answers

    Propose an explanation for why the regulatory protein in model 3 is called an 'activator' protein.

    <p>It is called an activator protein because the operon will not be activated unless the protein is bound.</p> Signup and view all the answers

    Compare and contrast the positive control mechanism of model 3 with the negative control mechanism in models 1 and 2.

    <p>Negative control involves repressor proteins that inhibit gene expression, while positive control requires transcription factors to enable transcription initiation.</p> Signup and view all the answers

    Choose one of the models in the activity. What conditions would need to be present in the cell to reverse the regulatory conditions?

    <p>In model 2, the compressor molecule would need to be removed from the environment to turn 'off' the operon.</p> Signup and view all the answers

    Some mutations can disable genes. What might be the result of such a mutation within the LAC regulatory region of the LAC operon?

    <p>The monomers won't break up.</p> Signup and view all the answers

    Describe the 4 combinations of active or inactive regulatory proteins that could be present at any time in the cell.

    <p>Active repressor, active activator, inactive activator, inactive repressor.</p> Signup and view all the answers

    Describe the cellular environment(s) that would turn the operon 'on'.

    <p>The answers depend on the kind of operon being studied.</p> Signup and view all the answers

    Study Notes

    Operons in Prokaryotes

    • Inducible operon: Operon that can be activated to produce enzymes when needed.
    • Repressible operon: Operon that is usually active but can be deactivated when enough product is present.

    Components of an Operon

    • Promoter: DNA region where RNA polymerase binds to initiate transcription.
    • Operator: Acts as an on/off switch for gene expression.
    • Terminator: Sequence where transcription ends.

    Transcription Mechanism

    • RNA polymerase binds at the promoter, moving from 3' to 5' direction.
    • Successful transcription depicted when mRNA and proteins are being produced.

    Regulatory Proteins

    • Repressor protein: Inhibits transcription by binding to the operator when active.
    • Inducer molecule: Binds to repressor, changing its shape to allow transcription.
    • Corepressor: Binds to repressor, activating it to block transcription.

    Lac Operon Behavior

    • Low lactose: Repressor binds to operator, preventing transcription and enzyme production for lactose metabolism.
    • High lactose: Presence of allolactose allows transcription initiation for lactose breakdown into glucose and galactose.

    Models of Operon Function

    • Model 1: Illustrates the induction of an operon where repressor blocks transcription.
    • Model 2: Shows a repressible operon activated by a corepressor to prevent ongoing gene expression.
    • Model 3: Demonstrates positive control requiring an activator protein for transcription initiation.

    Comparison of Operon Types

    • Inducible operons: Typically respond to environmental changes, activating when nutrients are present.
    • Repressible operons: Usually active and can be turned off when excess product is available, conserving energy.

    Gene Regulation Evolution

    • Operons enable coordinated gene expression in prokaryotes through a single mRNA molecule, optimizing energy use.

    Regulatory Protein States

    • Active repressor blocks transcription.
    • Active activator enhances transcription.
    • Inactive repressor does not inhibit transcription.
    • Inactive activator requires signaling to activate transcription.

    Mutations and Their Impact

    • Mutations in the lac operon regulatory region can prevent the breakdown of lactose, affecting cellular metabolism and energy use.

    Conditions for Operon Activation

    • Presence of signaling molecules (inducers or substrates) and absence of repressor activity are necessary conditions for operon activation.

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    Description

    Test your knowledge on the components and mechanisms of operons in prokaryotes. This quiz covers topics such as inducible and repressible operons, transcription regulation, and the behavior of the lac operon. Perfect for students of genetics or molecular biology.

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