Transcription Flashcards
What is the initiation site of transcription?
Promoter
What are the components of a transcription unit?
Promoter
Structural gene
Terminator
*Eukaryotes also have enhancers
What is the enzyme used in prokaryotes for transcription and its factors?
RNA polymerase
Sigma factor for initiation
Rho factor for termination
Contains two zinc molecules
In what direction is RNA synthesized
5’ to 3’
What does RNA pol lack compared to DNA pol?
Proofreading activity
Does not need primer
What is the promoter site in prokaryotes?
Upstream of start codon that contains consensus sequence
~35 nucleotides upstream is TTGACA
~10 nucleotides upstream is TATA box (Pribnow) TATAAT
What is released at beginning of elongation in prokaryotes?
Sigma factor
What are the two types of termination in prokaryotes?
Rho factor dependent
Rho factor independent
What is rho factor dependent termination?
Termination sequence recognized by rho factor
ATPase with helicase activity that disrupts RNA-DNA complex
What is rho factor independent termination?
Palindromic sequences - self-complementary
Creates hairpin structure that disrupts RNA pol
String of Us causes RNA to dissociate from DNA template
More common
What are some antibiotic inhibitors of prokaryotic transription?
Rifampin
Actinomycin
What are the 3 RNA pol in eukaryotes?
RNA pol I
RNA pol II
RNA pol III
What is the function of RNA pol I?
Synthesizes pre-rRNA 28S, 18S, 5.8S in nucleolus
What is the function of RNA pol II?
Synthesizes pre-mRNA in nucleus
What inhibits RNA pol II?
alpha-amanitin
What is the function of RNA pol III?
Synthesizes pre-tRNA in nucleus
Synthesizes pre-rRNA 5S in nucleolus
Synthesizes some snRNA and snoRNA
What encodes transcription factors?
Trans-acting elements
Where can TFs bind?
Core promotor site
Close to gene
Distal to gene
What is the function of TFs?
Assembly of transcriptional complex at promoter
Determination of what genes are transcribed
What are general TFs?
Required for all genes
Near start site - assembly of initiation complex
Recognize promoter, recruit RNA pol, and initiate transcription
What are specific TFs and their functions?
Stimulate or repress particular genes
Transacting factors
Modulate frequency of initiation
Mediate response to signals
Bind to coactivators
What are two examples of proximal regulatory elements?
CAAT box
GC box
What are the events in initiation?
TFIID binding to TATA box
TFIIF recruits pol II to TFIID
TFIIH has helicase activity
What is an exon?
Gene segment that codes for protein
What is an intron?
Noncoding sequence the interrupts exons of a gene
What is rRNA PTM?
RNAses remove introns and cleave into subunits
In nucleolus
What is tRNA PTM?
Removal of introns
Base modification
CCA added to 3’ end
In nucleus
What is mRNA PTM?
None in prokaryotes
Co and post in eukaryotes
5’ cap
Poly-A-tail to 3’ end
Removal of introns
Alternative splicing
In nucleus
How does 5’ cap occur and what is its function?
Enzymes Guanyl transferase and Guanine methyl transferase
Stabilize mRNA
Ribosome binding site
Efficient translation
What is poly-A-tail and its function?
Addition of 200-250 A residues in response to AAUAAAA signal by polyadenylate polymerase
Stabilizes mRNA
Facilitates exit from nucleus
Aids translation
Prevents degradation
How does splicing occur?
snRNA form snRNP that mediate splicing
What are p-bodies?
Processing bodies
Site of mRNA degradation and storage
Cytoplasmic RNP
