DNA Transcription Flashcards
What is the function of ribosomal RNA?
Forms ribosomes
What is the function of microRNA miRNA?
- Regulates gene expression
- Target mRNA molecules -> bind via base pairing
- Block translation into protein
What is the function of small interfering RNA (siRNA)?
- Regulates gene expression
- Cause degradation of mRNA
What is the function of small nuclear RNA (snRNA)?
Splices pre-mRNA
What does RNA polymerase not require?
A primer
What does RNA polymerase bind to and what does this require?
Binds promoter regions of DNA
- Requires transcription factors (proteins)
How many RNA polymerases do prokaryotes contain?
One RNA polymerase
- Multi subunit complex which makes all types of RNA
How many RNA polymerases do eukaryotes contain?
RNA polymerase I II and III
What does RNA polymerase I synthesise?
most rRNA (5.8S, 18S, 28S)
What does RNA polymerase II synthesise?
mRNA
What does RNA polymerase III synthesise
rRNA (5S), other RNA
What does Alpha amanitin (Amanita phalloides) (death cap mushroom) inhibit?
RNA polymerase II
- Causes liver failure
What antibiotic can inhibit bacterial RNA polymerase?
Rifampin
What chemotherapy drug can inhibit RNA polymerase?
Actinomycin D
What do prokaryotes have that act as transcription factors?
Protein factor (sigma factor)
What do transcription factors (TFIID, TFIIB, TFIIE) bind to to initiate transcription?
RNA polymerase II
What are promoters?
DNA regions that are not transcribed
- They bind RNA polymerase and transcription factors
- Bound RNA polymerase and open double helix
Name some promoter regions of DNA
- TATA box
- CAAT box
- GC box
What do DNA enhancers do?
DNA sequences that increase the rate of transcription
- May be upstream or downstream of the gene they regulate
- Stabilise TF and RNA polymerase to enable more transcription
Transcription factors that bind to enhancers are known as what?
Activators
How can an enhancer be many NTs away yet still enhance nearby DNA?
It is geometrically close due to DNA coiling
DNA sequences that decrease the rate of transcription are known as what?
Silencers
What do Silencers prevent?
RNA polymerase binding
Silencers bind to TF known as what?
Repressors
- Prevent RNA polymerase binding preventing transcription
What is the function of the 5’ untranslated region of mRNA??
Recognised by ribosomes to initiate translocation
What is the function of the 3’ untranslated region of DNA?
Important for post-transcriptional gene expression
Do introns or extrons leave the nucleus to become translated?
Extrons - exit nucleus
What is the initial transcription of RNA called? (contains introns and extrons)
hnRNA
What are the 3 key modifications that occur before RNA leaves the nucleus?
- 5’ capping
- Splicing out of introns
- 3’ polyadenation
What is 5’ capping?
Addition of 7-methylguanosine to 5’ end
- Added soon after transcription begins
- Distinguishes mRNA from other RNA
What is the 5’ splice site of the intron coded with?
GU
What is the 3’ splice site of the intron coded with?
AG
What base is highly concentrated in snRNP
Uridine
- 5 different U-RNPs identified
- U1, U2, U4, U5 and U6
RNA splicing occurs after the formation of what?
What does mRNA join with?
snRNPs combines with mRNA to form a splicesome
What is the loop of mRNA called with the intron?
Lariat
- Released with the intron to form the exons
What are anti-smith (Anti-Sm) antibodies antibodies against?
proteins in snRNPs
What condition has anti-sm antibodies?
SLE
- antibodies against snRNPs
What do anti-RNP antibodies attack?
U1 RNA (type of sn-RNP)
What conditions are associated with anti-RNP (U1 RNA) antibodies?
Mixed Connective tissue disease (mainly)
Also:
- SLE
- Scleroderma
What does alternative splicing allow for?
Many proteins from the same gene
Splicing errors can lead to what diseases?
- Beta thalassemia
- Oncogenesis - many splice site mutations/errors described
What are the bases which code for 3’ Polyadenylation?
AAUAAA followed by 10-30 NTs then CA
What are the 3 enzymes involved in 3’ Polyadenylation?
- Cleavage and polyadenylation specificity factor (CSF) (AAUAA)
- Cleavage stimulation factor (CstF) (CA)
- Poly-A polymerase (PAP) (after transcription is terminated)
What enzyme binds to AAUAA (3’ Polyadenylation)?
Cleavage and polyadenylation specificity factor (CSF)
What enzyme binds to CA sequence (3’ Polyadenylation)?
Cleavage stimulation factor
What does Poly-A polymerase (PAP) add to the 3’ end of mRNA?
~ 200 Adensoine nucleotides
What can extensive binding of Micro RNA (miRNA) cause the removal of on mRNA?
poly-A tail
- Exposes mRNA to degradation
- Essentially modifies gene expression at mRNA level
What are P-bodies? (processing bodies)
When miRNA binds to mRNA less extensively some mRNA can be moved to the P-bodies in the cytoplasm
- can cause mRNA to be sequestered from ribsomes meaning no translation
- When P-bodies hold the mRNA they can be degraded or held until a later point and then translated
