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Transcription in Prokaryotes quiz #1

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  • Which of the following statements best describes the termination of transcription in prokaryotes?
    Termination of transcription in prokaryotes occurs via three main mechanisms: rho-dependent termination, which requires the rho protein; rho-independent termination, which does not require the rho protein; and intrinsic termination, which involves weak uracil bonds in the RNA causing the transcript to dissociate from the DNA template.
  • What is the role of the sigma factor in prokaryotic transcription initiation?
    The sigma factor provides specificity to the RNA polymerase holoenzyme, allowing it to recognize and bind to the correct promoter sequence for the type of RNA needed by the cell.
  • Where is the Pribnow box located relative to the transcription start site in prokaryotes?
    The Pribnow box is located 10 base pairs upstream of the transcription start site and serves as a key promoter sequence.
  • How does the transcription bubble function during elongation in prokaryotic transcription?
    The transcription bubble is a region of about 18 nucleotides where the DNA is unwound and actively being transcribed by RNA polymerase.
  • What distinguishes consensus sequences in prokaryotic promoters from conserved sequences?
    Consensus sequences are similar but not identical across prokaryotic species, whereas conserved sequences are nearly the same in all organisms.
  • What is polycistronic mRNA and how is it processed in prokaryotes?
    Polycistronic mRNA contains multiple genes transcribed together in a single RNA strand, which must be further processed to separate individual genes for translation.
  • What happens to the sigma factor after transcription termination in prokaryotes?
    After termination, the sigma factor dissociates from the RNA polymerase, allowing the enzyme to be recycled for another round of transcription.
  • How does the location of the termination sequence relate to the actual site of transcript termination?
    The termination sequence is found upstream of the actual termination site, signaling proteins to help terminate transcription downstream of the sequence.
  • What is the function of the RNA polymerase holoenzyme in prokaryotic transcription?
    The RNA polymerase holoenzyme, which includes the core enzyme and sigma factor, initiates transcription by binding to promoter sequences on DNA.
  • How does prokaryotic transcription differ from eukaryotic transcription regarding mRNA structure?
    Prokaryotic transcription can produce polycistronic mRNA containing multiple genes, while eukaryotic transcription typically produces monocistronic mRNA with only one gene per transcript.
  • To which DNA sequence does bacterial RNA polymerase bind during the initiation of transcription in prokaryotes?
    Bacterial RNA polymerase binds to promoter sequences during transcription initiation, specifically to consensus sequences such as the Pribnow box (located 10 base pairs upstream of the transcription start site) and a 35 base pair consensus sequence upstream of the start site.
  • How many types of RNA polymerases are present in bacteria, and what is their role in transcription?
    Bacteria have a single type of RNA polymerase, which transcribes all types of RNA. Its specificity for different RNA types is determined by the associated sigma factor.