MolBio7 - 41 Flashcards
What are the 4 types of RNA?
mRNA, tRNA, rRNA, snRNA
Describe mRNA
Messenger RNA, codes for proteins, 3-5% total RNA
Describe tRNA
Transfer RNA, participates in translation, 49 families, each carries amino acid and has a specific anti-codon loop
Describe rRNA
Ribosomal RNA, major constituent of ribosomes, 4 main types
What is a stem-loop, and how is it formed?
Hair-pin RNA secondary structure caused by Watson-Crick pairing, or sometimes not - G=U can occur
Can RNA form tertiary structures?
Yes - tRNA is 3D
What is RNA polymerase?
Enzymes performing RNA synthesis
How many types of RNA polymerase are there?
3
What does RNA polymerase I do?
rRNA synthesis
What does RNA polymerase II do?
Protein-coding transcript synthesis
What does RNA polymerase III do?
tRNA, snRNA and 5S rRNA
Where does RNA polymerase bind?
Specific promotor locations
What direction does RNA synthesis proceed?
5’ > 3’
What supplementary actions does RNA polymerase also perform?
Unwinds DNA in front, re-anneals behind
What occurs to RNA transcript once transcribed?
PolyA tail added for stability and dissociation from the DNA
Name 4 core RNA promoters
TATA box, Inr, DPE, BRE
What does TBP stand for?
TATA binding protein
What does TF stand for?
Transcription factor
Which promoter does TFII bind?
Inr - initiator
Which promoter does TBP bind?
TATA box
What does BRE stand for?
TFIIB Recognition Element
Which promoter does TFIIB bind?
BRE
Outline transcription initiation
TBP binds TATA box, TFIIA binds to stabilise, TFIIB forms bridge that facilitates binding of complex to promoter, RNA polymerase binds (associated with TFIIF,G+H)
Describe the mediator complex
Huge complex, >20 subunits, binds to the C-terminal tail of RNA Polymerase II to ensure high levels of transcription
What does the mediator complex do?
Facilitates association with timing/location control factors, and constructs/remodells chromatin
What three processes are applied to RNA once transcribed?
5’ capping, intron splicing, PolyA tail addition
Outline 5’ capping
Added when mRNA is 20-40 nucleotides long, involves unusualis 5’-5’ linkage of guanosine that is then methylated
What is the purpose of 5’ capping?
Tells translational machinery where the start is
Up to how many A can be added in PolyA?
200
What is the PolyA signal?
AAUAAA
What three proteins facilitate PolyA creation?
CstF, CPSF, CTD, PAP
What does CstF stand for?
Cleavage stimulating factor
What does CPSF stand for?
Cleavage and polyadenylation specific factor
What does CTD stand for?
PollII C-terminal domain
What is the relationship between PolyA and RNA stability?
Longer tail, more stable
What does PAP stand for?
PolyA binding protein
Why is splicing important?
Machinery of cell not capable of ignoring sections of RNA during translation
Where do introns appear?
DNA and pre-mRNA, not in mRNA
Outline splicing
DIAGRAM, 2’OH of branch site attacks bond on donor site, cleavage and formation of lariat, 3’OH of donor site attacks acceptor site, freeing lariat, which is then degraded
What are snRNPs?
Small nuclear ribonuclear proteins (snRNA + U1-2,4-6)
What are the three functions of snRNPs?
Recognition of 5’ donor branch sites, brinding of sites together, catalysis of RNA cleavage
