Week 9

    Cards (68)

    • What enzyme carries out transcription?
      RNA polymerase
    • What is the composition of RNA polymerase in E. coli?
      Multiple subunits including β and α
    • What role do magnesium ions play in transcription?
      They are ubiquitous in nucleic acid enzymes
    • Where is the active center of RNA polymerase located?
      In the middle of the complex
    • How does RNA polymerase initially move to the promoter of a gene?
      By diffusion in the cytoplasm
    • What happens when RNA polymerase encounters DNA?
      It binds unspecifically to the DNA
    • What does the RNA polymerase complex do after binding to DNA?
      Slides along the DNA in a one-dimensional walk
    • What is the role of a promoter in transcription?
      It aids RNA polymerase to the gene's start
    • How does the strength of a promoter affect RNA polymerase interaction?
      The closer it resembles the consensus sequence, the stronger the interaction
    • What does the σ70 factor do in transcription?
      Allows specific interaction with –10 and –35 regions
    • What happens when cells are stressed regarding σ factors?
      They produce other σ factors
    • What is formed when a promoter is bound by RNA polymerase?
      An open complex
    • What is the approximate rate of RNA synthesis by RNA polymerase?
      3050 nucleotides per second
    • What are the two main mechanisms for termination of transcription?
      GC hairpin formation and Rho interaction
    • What is the accuracy of transcription in vivo?
      Approximately 1 × 105^{-5}
    • What is the half-life of mRNA in bacteria?
      Approximately 7 minutes
    • What happens during head-on collisions between replication forks and transcription complexes?
      They are highly problematic
    • What is the role of activator proteins in transcription?
      They help recruit RNA polymerase complexes
    • How do repressor proteins affect transcription?
      They prevent RNA polymerase binding
    • What is the regulation of the lactose operon based on?
      Several levels of regulation
    • What does permease do in the lactose operon?
      Allows active transport of lactose into the cell
    • What happens to lacI when lactose is present?
      Lactose binds and changes the repressor's shape
    • What are the two basic forms of transcriptional regulation in bacteria?
      1. Activation of transcription
      2. Repression of transcription
    • What are the mechanisms of repression in transcription?
      • Repression by steric hindrance
      • Repression by looping
      • Repression by modulation of an activator
    • What are the components of the lactose operon?
      • lacI (repressor)
      • lacZ (β-galactosidase)
      • lacY (permease)
      • lacA (O-acetyltransferase)
    • What is the process of lactose metabolism in the cell?
      1. Lactose enters the cell via permease
      2. Lactose is isomerized into allolactose
      3. Allolactose binds to the repressor
      4. Transcription of lac operon occurs
    • What are the roles of GreA and GreB in transcription?
      • They fit into the secondary channel of RNA polymerase
      • Activate endonuclease activity to remove mis-incorporated nucleotides
    • What are the consequences of backtracking during transcription?
      • Pauses elongation
      • Leads to stable RNA polymerase complexes
    • What is the significance of the consensus sequence in transcription?
      • Determines the strength of RNA polymerase interaction with the promoter
    • What are the effects of stress on σ factors in bacteria?
      • Cells produce alternative σ factors for stress responses
    • What is the role of the σ70 factor in transcription?
      • Facilitates specific binding of RNA polymerase to the promoter regions
    • What is the relationship between transcription and replication in bacteria?
      • Head-on collisions between replication forks and transcription complexes are problematic
    • How does the cell regulate the expression of the lactose operon?
      • Through activators and repressors that modulate RNA polymerase binding
    • What is the role of the lacI gene?
      It produces a repressor for the lac operon
    • Why is the lacI gene expressed permanently?
      It is under control of a weak promoter
    • What does the repressor do in the lac operon?
      It binds to the operator and represses expression
    • What is the structure of the repressor formed by lacI?
      It forms a tetramer that binds to the operator
    • How does lactose availability affect the lac operon?
      Lactose binds the repressor, changing its shape
    • What happens to the repressor when allolactose binds to it?
      It will not bind the operator anymore
    • What is the role of the CAP protein in the lac operon?
      It allows strong transcription when bound
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