lec25 Flashcards
gene expression in euks vs proks
π¦ Prokaryotes:
No nucleus β transcription and translation happen simultaneously.
Genes are in operons β multiple genes under one promoter β 1 mRNA = multiple proteins (polycistronic).
Less regulation β no chromatin, so DNA is always accessible.
Regulation mostly negative β repressors block transcription.
𧬠Eukaryotes:
Nucleus present β transcription and translation are separated (transcription in nucleus, translation in cytoplasm).
One gene per mRNA β monocistronic.
DNA is wrapped in chromatin β requires chromatin remodeling to access.
Regulation is mostly positive β needs activators, enhancers, mediator complex, chromatin remodelers.
Pre-mRNA gets processed β 5β cap, splicing, polyA tail.
uracil lacks the ________ _______ seen in thymine but this does not affect its Watson-Crick base-pairing with adenine
methyl group
mRNA
concentration depends on two factors
the rate of mRNA synthesis
* the rate of mRNA degradation
The three elements of gene control
prokaryotes
in
are, in order of importance:
- transcription initiation
- RNA turnover (nuclease degradation)
- transcription termination
whch strand of dna has same seq (except for u) as ssrna
coding strand, template strand is complementary.
What are the roles of the -35 and -10 regions in prokaryotic transcription initiation?
-35 region: Recognized and bound by the sigma factor, helping position RNA polymerase at the promoter.
-10 region (Pribnow box): Helps with RNA polymerase binding and DNA unwinding for transcription initiation.
(Note: The -10 region is similar in function to the TATA box in eukaryotes.)
𧬠DNase I Footprinting
π Concept:
Used to map protein binding sites on DNA.
DNase I cuts unprotected DNA regions.
Fewer bands appear when proteins block DNase I from cutting DNA.
π¬ Key Idea:
Transcription factors protect DNA, leading to less cutting β fewer bands on the gel.
π‘ Why It Matters:
Helps scientists find where proteins bind to regulate gene expression.
𧬠Transcription Initiation: Prokaryotes vs. Eukaryotes
π¦ Prokaryotes:
Key Factor: Sigma factor guides RNA polymerase to promoter.
Promoter Regions: -10 (TATA box) & -35 recognized by sigma factor.
Simple Start: RNA polymerase binds directly & begins transcription.
𧫠Eukaryotes:
Key Players: Histone acetylation, CRC (Chromatin Remodeling Complex), TAP (Transcription Activator Protein), TBP (TATA Binding Protein).
Complex Start: RNAP II needs transcription factors (TFIID includes TBP) for promoter recognition.
Enhancers & Coactivators help RNAP II recruit TAP for stronger initiation signals.
π Key Difference: Prokaryotes use sigma factor for direct binding, while eukaryotes require multiple proteins to modify chromatin & recruit RNAP II!
when is sigma factor released
Sigma is released after RNA polymerase clears the promoter and begins elongation.
prok terminations
πΉ Rho-dependent Termination:
β Rho protein (Ο) binds to rut site (CA-rich RNA sequence). β Rho moves along RNA using ATP energy. β Rho catches RNA polymerase, disrupts RNA-DNA pairing, and ends transcription (acts like a helicase).
πΉ Rho-independent Termination:
β RNA transcript forms a GC-rich hairpin loop near the end. β Hairpin destabilizes RNA-DNA hybrid. β Followed by UUU sequence, which creates weak A-U base pairing β RNA falls off, ending transcription.
What is the role of the rut site in Rho-dependent termination?
Itβs a CA-rich sequence where Rho protein binds and starts chasing RNA polymerase.
primary mechanism of gene regulation in prokaryotes
transcription initation
What are the two key factors that determine mRNA concentration in bacteria?
A) Rate of translation and rate of transcription B) Rate of RNA splicing and exon skipping C) Rate of mRNA synthesis and rate of mRNA degradation D) Rate of enhancer binding and chromatin remodeling
Answer: C) Rate of mRNA synthesis and rate of mRNA degradation
What is the function of the UP element in bacterial transcription?
recruits sigma factor to begin transcription
