Lecture 2/21/25 Flashcards
Bacterial Transcription
What is abortive initiation?
A phase where RNA polymerase makes and releases short RNA fragments before elongation begins.
Which channel does the sigma factor block?
The RNA exit channel during transcription initiation.
When does the sigma factor dissociate?
After promoter clearance, allowing transcription elongation.
What is ATP-dependent melting in transcription?
A process that uses AAA+ proteins and ATP to quickly form an open complex at the promoter.
What is ATP-independent melting?
Promoter melting mediated by sigma factors that does not require ATP but occurs more slowly.
What proofreading mechanisms does RNA polymerase use?
Kinetic proofreading (exonuclease activity and pyrophosphorolysis) and nucleolytic proofreading (endonuclease activity).
Why is a higher error rate acceptable in RNA transcription?
Because RNA is transient and errors do not affect long-term genetic information.
Question
Answer
How does Rho-independent termination work?
A GC-rich inverted repeat is transcribed to form a hairpin, causing RNA polymerase to pause and release the RNA.
Why is the hairpin structure important?
It destabilizes the RNA-DNA hybrid, promoting transcript release.
What is the difference between stop codons and termination sequences?
Stop codons signal the end of translation; termination sequences signal the end of transcription.
How does Rho-dependent termination function?
Rho protein binds to the RUT site on RNA, moves toward RNA polymerase using ATP, and unwinds the RNA-DNA hybrid to terminate transcription.
What is the role of Rho protein?
It is an ATP-dependent helicase that disrupts the RNA-DNA hybrid, ending transcription.
How does Rho-independent termination work?
A GC-rich inverted repeat is transcribed to form a hairpin, causing RNA polymerase to pause and release the RNA.
Why is the hairpin structure important?
It destabilizes the RNA-DNA hybrid, promoting transcript release.
What is the difference between stop codons and termination sequences?
Stop codons signal the end of translation; termination sequences signal the end of transcription.
How does Rho-dependent termination function?
Rho protein binds to the RUT site on RNA, moves toward RNA polymerase using ATP, and unwinds the RNA-DNA hybrid to terminate transcription.
What is the role of Rho protein?
It is an ATP-dependent helicase that disrupts the RNA-DNA hybrid, ending transcription.
