L11: Bacterial Transcription

• What are the three main processes of information flow in cells?

  DNA replication, transcription, and translation
• How can gene expression be regulated?

  At the level of transcription or translation, or both
• What base substitutes for thymine in RNA?

  Uracil (U)
• What are the two strands of DNA called in transcription?

  Template strand (antisense) and non-template strand (sense)
• Why is uracil not found in DNA?

  Because cytosine can undergo spontaneous deamination to produce uracil, which could lead to mutations
• What are the three major classes of bacterial RNA?

  mRNA, rRNA, and tRNA
• What is the role of the promoter in bacterial transcription?

  It attracts and binds RNA polymerase and signals the start of transcription
• What subunits compose the core RNA polymerase in bacteria?

  α, β, β’, and ω subunits
• What is the function of the σ subunit in bacterial RNA polymerase?

  It directs the polymerase holoenzyme to a gene promoter
• What technique is used to identify promoters in DNA?

  DNA footprinting technique
• What are the two regions typically protected by RNA polymerase in a bacterial promoter?

  The -10 sequence and the -35 sequence
• In which direction is RNA built during transcription?

  In the 5’ to 3’ direction
• What are the three stages of transcription?

  Initiation, elongation, and termination
• What happens during the initiation stage of transcription?

  RNA polymerase holoenzyme binds the promoter and opens the DNA double helix
• How many σ factors does Escherichia coli have?

  Multiple σ factors
• What is scrunching in the context of transcription initiation?

  It is when the polymerase pulls downstream DNA towards itself, converting the closed promoter complex to an open promoter complex
• How many base pairs are unwound during the initiation of transcription?

  12 to 15 base pairs
• What is the length of the RNA:DNA hybrid during elongation?

  Approximately 8 base pairs long
• What happens if RNA polymerase mis-incorporates a ribonucleotide?

  It hesitates, back-tracks, removes the nucleotide, and then continues
• What are the two mechanisms of transcription termination in bacteria?

  Rho-independent and Rho-dependent termination
• What is a characteristic of Rho-independent termination of transcription?

  A palindromic GC-rich sequence followed by a T-rich sequence
• What is the role of the Rho protein in transcription termination?

  It disrupts the DNA:RNA hybrid helix, releasing the RNA
• How does rifampicin affect bacterial transcription?

  It inhibits RNA polymerase by binding tightly to the RNA exit channel
• What does bending of DNA by RNA polymerase facilitate?

  It allows the DNA duplex to be opened more easily