Lecture 19 Flashcards
What are the initiation factors for prokaryotes?
IF1, IF3
what are the elongation factors for prokaryotes?
Ef-Tu/Ts, EF-G (EF1, EF2)
what are the termination factors for prokaryotes?
RF1 - RF3
what are the initiation factors for eukaryotes?
eIF1 - eIF5
what are the elongation factors for eukaryotes?
eEF1, eEF2
what are the termination factors for eukaryotes?
eRF1, eRF3
what do prokaryotes use to find their initiation sites for translation?
shine-Delgarno box which is generally located 8 base pairs upstream of the start codon
what do eukaryotes use to find their initiation sites for translation?
40S ribosomal subunit interaction with 5’ methylated cap of mRNA
how does streptomycin disrupt bacterial translation?
binds to the 16S rRNA of the 30S subunit of the bacterial ribosomes and messes up base pairing, causing miscoding during elongation
how does puromycin disrupt bacterial translation?
imitates AA-tRNA and causes premature ejaculation of the nascent protein.
- similar to dideoxy sequencing
how does diphtheria toxin work?
it is a protein that gets cleaved into two fragments, A and B
- B causes internalization of the toxin
- A is an enzyme that attaches an ADP ribose on eEF2 which poisons translation
Why can’t puromycin be used as an antibiotic?
It affects eukaryotes
What is a main sign of diphtheria?
Thick grey leathery coating in the throat
What is ricin?
It is a protein toxin that is found in castor bean. It is insoluble in castor oil and one bean can kill a child.
How does ricin work?
Two chains
1) B gets the toxin within the cell
2) A inactivates a specific A residue on the ribosomes making it nonfunctional.
What level do aminoglycoside antibioitics act at?
The level of initiation
What level do tetracycline and spectinomycin work at?
The loading step
What does chloramphenicol do as an antibiotic?
Acts against peptidyl transferase
How much energy does the charging of tRNA consume?
2 ATP
How much energy is used every time the ribosomes moves along the codon using elongation factors?
1 GTP
How much energy does termination use?
1 GTP
How many high energy bonds are utilized for every amino acid polymerized?
4 (ATPs or GTPs)
What is the purpose of ferretin protein?
It controls the intracellular concentration of iron by binding to it and titrating it down to appropriate levels.
What is the reason eukaryotic mRNA is circular?
The initiator complex binds both the 5’ cap and the 3’ poly A tail. The reason is that when the ribosome begins at the 5’ end of the mRNA it will make its way around the circle like a lap and end back at the initiation complex where it can then restart almost immediately if allowed to.
How is ferretin regulated?
There is an Iron Response Element (IRE) located in the 5’ UTR region just before the ferretin mRNA. This IRE is usually in a stem loop that is bound by IRE-Binding Protein. When there is high concentration of iron, the IRE-BP gets bound by iron and releases the IRE stem loop, allow the ferretin mRNA to be translated.
Describe what happens in Hereditary Hyperferrinemia - Cataract Syndrome.
There is a mutation in the Iron Response Element that prevents it from being bound in the stem loop conformation and allows perpetual translation of the ferretin protein which eliminates iron and causes cataracts.
How is initiator tRNA regulated?
Met-tRNA normally forms a complex with eIF2 and GTP that drops it off at the ribosomes for translation and the GTP in this complex is usually hydrolyzed to GDP. In order for it to start over it first needs to be converted back into GTP by eIF2B.
- BUT if eIF2B is phosphorylates by something, it becomes inactive and initiation can’t begin.
What is vanishing white matter and what causes it?
A neurological deterioration exacerbated by head trauma where the white myelin vanishes.
- a mutation in any of the 5 subunits of eIF2B will cause this.
