Lecture 17 Flashcards
Where is polymerase I most active?
nucleolus
What is RNA polymerase I responsible for?
- makes ribosomal RNA genes (rRNA)
What is RNA polymerase III responsible for?
- makes rRNA and tRNA
What is RNA polymerase II responsible for?
- makes mRNA
- makes ribosomal proteins
What is the role of exosomes?
Degrades abnormal RNA
What does miRNA do?
Inhibits translation of mRNA
What are the steps of 5’cap on eukaryotic mRNAs?
1) phosphohyrolase removes the gamma phosphate from the pre-mRNA
2) GTP gets cleaved, losing two phosphates and subsequently binds to the beta phosphate on pre-mRNA
3) Guanine from GTP gets methylated from S-adenosine-methionine
What is unusual about the 5’cap on eukaryotic mRNA? Why is this important?
Its a 5’ to 5’ linkage as opposed to 5’ to 3’.
- this inhibits ribonuclease activity
What is the recognition sequence for poly-adenylation?
- AAUAAA
What mediates poly adenylation?
PAP (polyA polymerase)
Where does the recognition sequence for poly-adenylation actually appear on the DNA sequence?
10-30 bases upstream of the site that actually gets polyadenylated
How long is the poly A tail
Around 200 bps long
What does the Poly A binding protein do?
It binds the entire poly A tail
What does the poly a tail do?
Protects the mRNA from degradation
Where is the methylated cap found on the mRNA and where is the poly A tail found?
5’ cap and poly A tail, dude.
What percent of mRNA are alternatively spliced?
90%
alternative splicing is when two mRNA from the same gene can be made up of different exons
What are three ways to alternative splicing can alter the mRNA derived from the same gene?
1) removal of exons on the interior of the mRNA
2) removal of exons near a poly U recognition sequence
3) use of different promoter regions
What does BcL-xS protein do?
Stimulates apoptosis in lymphocytes
What does Bcp-xL protein do?
Inhibits apoptosis in brain
What is the sequence at the beginning of introns?
G U
What is the sequence at the end of introns?
A G
What are the reactions used in splicing?
Two transesterification reactions
breaking and forming of two phosphodiester bonds
What are the steps of intron splicing?
1) A 2’ hydroxyl from the 3’ exons (latter exons) nucleophilic attacks the phosphate nearest the 5’ exons (former exons), cleaving the strand.
2) the 3’ hydroxyl from the now hanging 5’ exon nucleophilic attacks the 3’ exons (latter exons) and forms the final mRNA strand.
How does the HIV virus get around the fact that RNAs have to get completely spliced?
Through the use of the protein Rev which causes the viral RNA to be exported from the nucleus before it gets a chance to get spliced.
What are the pathways of eukaryotic mRNA degradation?
- Deadenylation
- Recapping
- Endonucleases
- nonsense-mediated mRNA decay via premature termination codons
