Advanced Microbiology Lecture 13: Gene Expression
33 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of the AdcR regulon?

  • Regulating the heat shock response in bacteria
  • Inducing genes in response to DNA damage
  • Managing the catabolism of carbon sources
  • Controlling the import and efflux of zinc (correct)

    • How does catabolite repression affect operon expression?

  • It promotes the expression of all operons equally.
  • It ensures preferential use of the best energy source. (correct)
  • It increases the expression of operons in response to glucose only.
  • It inhibits enzyme production in all metabolic pathways.

    • Which component of the two-component signal transduction system acts as the sensor?

  • Response regulator
  • Transcription factor
  • Histidine kinase (correct)
  • Heat shock protein

    • What role do heat shock proteins (Hsps) play in bacteria?

    <p>Assisting in the folding of denatured proteins.</p> Signup and view all the answers

    Which regulatory mechanism is primarily responsible for the overlap in bacterial global regulons?

    <p>Ability to respond to multiple environmental stresses.</p> Signup and view all the answers

    What is the primary role of an activator protein in positive regulation?

    <p>To enhance the binding of RNA polymerase to DNA</p> Signup and view all the answers

    How does a co-repressor function in gene expression regulation?

    <p>It inhibits an activator or activates a repressor</p> Signup and view all the answers

    What is the significance of riboswitches in bacterial gene regulation?

    <p>They change mRNA structure in response to metabolite binding</p> Signup and view all the answers

    In a negative repressible system of gene regulation, what is the function of the repressor protein?

    <p>To halt transcription in the presence of a co-repressor</p> Signup and view all the answers

    What type of regulation involves genes that are expressed unless turned off by a repressor?

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

    Which of the following processes occurs at the transcriptional regulation level?

    <p>Initiation of mRNA synthesis from DNA</p> Signup and view all the answers

    What does the term 'inducible' refer to in the context of gene expression?

    <p>Genes expressed only in the presence of certain stimuli</p> Signup and view all the answers

    What is the efficacy of posttranslational regulation in controlling gene expression?

    <p>It influences protein activity and stability after translation</p> Signup and view all the answers

    What is the primary role of sRNAs in the regulation of translation?

    <p>To block translation initiation by masking initiation regions</p> Signup and view all the answers

    Which of the following modifications is NOT commonly associated with posttranslational regulation?

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

    What is the purpose of feedback inhibition in metabolic pathways?

    <p>To modulate the activity of the initial enzyme based on the end product's concentration</p> Signup and view all the answers

    What defines a 'regulon' in bacterial global regulation?

    <p>Several distinct operons controlled by a single regulatory protein</p> Signup and view all the answers

    Why might an organism transcribe mRNA that is not immediately translated?

    <p>To prepare for rapid responses to fluctuating conditions</p> Signup and view all the answers

    Which statement accurately describes the sensitivity of translation regulation compared to elongation?

    <p>Translation initiation is more sensitive to mRNA structure than elongation.</p> Signup and view all the answers

    In two-component systems, what is the primary function of phosphorylation?

    <p>To act as a signal in transduction systems</p> Signup and view all the answers

    What environmental factors must bacteria adapt to rapidly?

    <p>Nutrient availability and temperature</p> Signup and view all the answers

    How does the binding of proteins or sRNAs typically affect the ribosomal binding site on mRNA?

    <p>Inhibits access by altering mRNA stability</p> Signup and view all the answers

    Which statement about global regulatory mechanisms in bacteria is true?

    <p>They allow coordinated regulation of multiple operons in response to environmental changes.</p> Signup and view all the answers

    What effect does tRNA without an attached amino acid have on gene expression?

    <p>Increases gene expression through base-pairing</p> Signup and view all the answers

    How do metabolite-binding riboswitches typically operate?

    <p>By binding directly to leader RNA in a metabolic pathway</p> Signup and view all the answers

    What is the relationship between mRNA half-life and protein production?

    <p>Increased mRNA half-life correlates with increased protein production</p> Signup and view all the answers

    What is the role of RNase E in the regulation of mRNA?

    <p>It triggers degradation of mRNA by binding to its own transcript</p> Signup and view all the answers

    Which type of RNA is primarily involved in posttranscriptional regulation in bacteria?

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

    What is an example of a molecule that can act as a ligand for a riboswitch?

    <p>Amino acids like lysine</p> Signup and view all the answers

    What happens when tRNA has an attached amino acid?

    <p>Formation of a terminator structure leading to decreased expression</p> Signup and view all the answers

    How might sRNAs influence bacterial physiology?

    <p>Through direct binding and regulation of proteins posttranscriptionally</p> Signup and view all the answers

    How are riboswitches implicated in biochemical pathways?

    <p>By regulating transcription based on ligand presence</p> Signup and view all the answers

    What is a key feature of small RNAs in bacteria?

    <p>They can form secondary structures such as stem loops</p> Signup and view all the answers

    Study Notes

    Advanced Microbiology: Lecture 13 - Gene Expression: Genes & Operons

    • Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product.
    • Negative regulation: genes in an operon are expressed unless turned off by a repressor protein.
    • Positive regulation: genes in an operon are not expressed unless turned on by an activator protein.
    • Regulation can be inducible (increased gene expression), repressible (decreased gene expression), or both.
    • Inducers: increase gene expression, activate an activator or inactivate a repressor.
    • Co-repressors: decrease gene expression, activate a repressor or inactivate an activator - Apo vs. holo protein: the differences between the inactive (apo) and active (holo) forms of a protein, typically related to ligand binding.

    Negative Regulation

    • Negative inducible system (lac operon - lactose):
      • In the absence of lactose, the repressor protein (lacI) is bound to the operator, preventing transcription.
      • In the presence of lactose, allolactose (inducer) binds to the repressor, changing its shape; the repressor detaches from the operator, allowing RNA polymerase to bind and transcribe the lac genes.
    • Negative repressible system (trp operon - tryptophan):
      • In the absence of tryptophan, the repressor protein (trpR) is inactive and cannot bind to the operator. Transcription occurs.
      • In the presence of tryptophan, tryptophan (co-repressor) binds to the repressor, activating it; the activated repressor binds to the operator, preventing transcription.

    Positive Regulation

    • Positive inducible system (ara operon - arabinose):
      • In the absence of arabinose, the activator protein (araC) is inactive and cannot bind to the promoter. Transcription is low.
      • In the presence of arabinose, arabinose binds to the activator, activating it; the activated protein binds to the promoter, increasing transcription.

    Regulation of Gene Expression

    • Transcriptional regulation: controls the rate at which genes are transcribed into mRNA.
    • Posttranscriptional regulation: controls the processing of mRNA and its stability.
    • Translational regulation: controls the rate at which mRNA is translated into protein.
    • Posttranslational regulation: controls the activity of proteins after they've been translated.

    Riboswitches

    • RNA elements in mRNA leaders that sense metabolites.
    • RNA folds into a 3D structure that allows a ligand to bind.
    • Ligand binding leads to a conformational change, altering terminator/anti-terminator alterations or changing access to the ribosomal binding site.

    T Box Mechanism

    • First discovered for gene expression of aminoacyl-tRNA synthetases in B. subtilis.
    • tRNA without an attached amino acid increases expression (anti-terminator forms).
    • tRNA with an attached amino acid decreases expression (terminator forms).

    Metabolite-binding Riboswitches

    • Small molecules can bind directly to leader RNA.
    • Typically involved in the same metabolic pathway.
    • Found for many types of molecules (atoms): amino acids (lysine), vitamins (B12), nucleic acid bases (guanine), cofactors (SAM), and metal ions (Mg).
    • Can regulate transcription through attenuation or blocking the transcription initiation region.

    Regulation of mRNA Degradation

    • Half-life: time taken for half of the template to be reduced.
    • Increased half-life leads to increased protein production.
    • RNase E targets its own RNA: Low RNase E increases mRNA message, and High RNase E degrades mRNA.

    Regulation by sRNAs (small RNAs)

    • Non-protein coding RNA involved in post-transcriptional regulation.
    • Individual bacteria may encode hundreds of sRNAs.
    • Can be encoded in intergenic regions, form secondary stem loop structures.
    • Implicated in the regulation of physiology, metabolism, and virulence.

    Mechanisms of sRNA-Interactions

    • sRNAs can inhibit translation by blocking the ribosome binding site, destabilizing target RNA by recruiting RNase, or enhance translation by exposing an occluded ribosome binding site or stabilizing target RNA.

    Regulation of Translation

    • Initiation of translation is sensitive to mRNA structure.
    • Proteins and sRNAs can bind mRNA and block translation initiation regions.
    • Similar mechanisms can lead to activation of translation, where bound proteins or sRNAs can disrupt secondary structure, exposing the ribosome binding site.

    Posttranslational Regulation

    • Not all polypeptides are active proteins; some require modification (modification examples: phosphorylation, acetylation, methylation).
    • Phosphorylation is a common signal in transduction systems.
    • Two-component systems are common examples.

    Posttranslational Regulation: Feedback Inhibition

    • End products of a pathway bind to the first enzyme in the pathway to inhibit its activity.
    • Common in biosynthetic pathways.
    • Highly sensitive and fast for modulating the amount of end product.
    • Trp operon is a good example.

    Important Questions

    • Why would an organism want so much regulation?
    • Why do these mechanisms occur at different levels?
    • Why make mRNA if not translating it?
    • Why use sRNAs instead of repressors/activators?

    Global Regulation: Regulons & Stimulons

    • Bacteria must adapt to various conditions (nutrient availability, moisture/desiccation, temperature).
    • Global regulatory mechanisms allow simultaneous regulation of multiple operons in response to environmental changes.
    • Regulon: a set of several operons controlled by a single protein.
    • Stimulon: a collection of regulons that respond to the same environmental condition. Examples: TrpR, LexA, and AdcR systems).

    Catabolite-sensitive Operons

    • Catabolites: smaller molecules resulting from the breakdown of larger molecules.
    • Energy is expended for the production of enzymes in catabolism.
    • Catabolite repression: cells preferentially utilize the most efficient energy source. Operons involved with using alternative carbon sources are frequently repressed when glucose is present (glucose effect).

    Stress Responses in Bacteria

    • Bacterial global regulons quickly respond to stress conditions (e.g., osmolarity, pH, temperature, metal availability, nutrient access).
    • Responses are flexible and can address multiple stressors at once.
    • E. coli heat shock response: unique heat shock proteins (Hsps) increase after temperature rise, supporting normal growth, protein folding, degradation of damaged proteins.
    • Dnak is a cellular thermometer, generally binding to and helping new proteins fold or assisting denatured proteins to refold.

    Signal Transduction Systems (STS) in Bacteria

    • Some gene regulation requires bacteria to sense external environment.
    • Two-component STS:
      • Histidine kinase: membrane-bound protein that senses environment and auto-phosphorylates.
      • Response regulator: intracellular protein that receives phosphate from histidine kinase and performs a regulatory function.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Lecture 13: Regulation of Gene Expression Pt. 2: MICR 321

    Description

    Explore the intricate mechanisms of gene expression in this quiz from Advanced Microbiology, Lecture 13. Learn about operons, negative and positive regulation, and the roles of inducers and co-repressors in gene activity. Test your understanding of the lac operon and other regulatory systems.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser