Translation Flashcards
What is the primary site of translation initiation?
5’ G cap
What is the secondary site of translation initiation?
AUG start codon and Kozak or Shine-Dalgarno sequence
What is the purpose of the Cap binding complex in translational initiation?
It recruits the small subunit of the ribosome to mRNA
How does the cap binding complex regulate translation?
It ensures that only mRNA’s that are capped are translated by binding to the cap and recruiting the small ribosomal subunit to the mRNA
What are the three subunits that make up eIF4F?
A, G, E (A+G+E = eIF4F)
What is the relationship between cancer cells and eIF4F?
Cancer cells have increased levels of eIF4F that leads to higher rates of translation
Which subunit of eIF4F is the limiting subunit?
E
Describe a weak mRNA?
A mRNA that is produced minimally under normal conditions and is produced en mass due to a response to a particular stimuli, these mRNA are weak and rapidly degraded
Describe a strong mRNA.
Always present, regulating normal cell conditions, constantly being transcribed in significant amounts
Define Polysome.
Multiple ribosomes lined up on a single mRNA translating the same protein simultaneously (direction of 5-3 and N to C)
What is the role of a tRNA?
Serves as an adaptor between nucleotide sequences and amino acids
The amino acid is bound to which end of the tRNA?
3’
What is considered the second genetic code?
The aminoacyl tRNA synthetases are proteins that match the correct tRNA with the correct amino acid. The information and function that takes place in pairing the two together is considered the second genetic code
How many different aminoacyl tRNA synthetases are present in a cell?
20
What does charging refer to?
Charging is the addition of an amino acid to a tRNA through the hydrolysis of ATP. When the AA is bound to the tRNA, the tRNA is considered charged
What is the sequence of events that leads to tRNA charging?
- AA and ATP are reacted to produce an adenylated AA (AA + AMP) and PPi is released. 2. The adenylated AA binds to the tRNA releasing the AMP added in the previous step. 3. Final products are charged tRNA (tRNA + AA), AMP and PPi
What is the function of eIF2?
eIF2 escorts the methionyl tRNA to the ribosome
What is the function of eIF1 and eIF3?
binds the small ribosomal subunit in place and interacts with the cap binding complex to bring the ribosome to the mRNA
What happens when AUG is recognized by the small ribosomal subunit?
The large ribosomal subunit combines with the small subunit
What causes the release of initiation factors?
The recognition of AUG
What is the name of the recognition sequence for Eukaryotes?
Kozak
What is the name of the recognition sequence for Prokaryotes?
Shine - Dalgarno
When does the large subunit join the ribosome?
Upon the small sub unit recognizing the start sequence
What does polycistronic imply? Is it pro or eukaryotic
Prokaryotic - polycistronic means multiple start sequences are present on a single mRNA allowing for different proteins to be made from a single mRNA
What does monocistronic imply? Is it pro or eukaryotic
Eukaryotic - monocistronic implies there is a single start sequence and a single protein can be made from one mRNA molecule
What is the Poly A Binding Protein (PABP)
PABP binds to the Poly A tail added to the mRNA that links the tail to the head creating a loop that allows for faster subsequent rounds of translation
Peptide Transferase is an example of a…
Ribozyme (it is an enzyme but not a protein, it is a mRNA molecule
The energy molecule that powers the peptide bond formation is…
ATP (hydrolysis)
What Elongation factor is responsible for translocation of the ribosome
EF2
What Elongation factor brings in new charged tRNA to the A site?
EF1
What is the sequence for translation WRT the ribosome during translation
- EF1 brings charged tRNA to empty A site. 2. peptide bond is created between polypeptide to new AA in the A site. 3. EF2 causes ribosome to move one position down the mRNA opening up the A site again
What causes termination?
Upon reaching the stop codon Release Factor binds to the A site and catalyzes the release of protein from tRNA and disassembly of the ribosome
What protein regulates eIF4E
4E Binding Proteins bind eIF4E sequestering them and slowing or stopping translation from occurring. 4EBP are “anti oncogenic”
What can cause stress response from the ER
Ca depletion Reduction of disulfide bonds Expression of mutant proteins misfiling proteins ischemia UV light exposure
What does a misfolded protein cause to happen
- Translation stops. Chaperone proteins come in to unfold the protein and allow it to refold correctly if possible
If protein accumulation continues what happens to the cell?
Apoptosis
What is the consequence of eIF2 being phosphorylated by PERK
eIF2 can no longer bring the methionyl tRNA to the ribosome
What is the underlying cause of Walcott-Rallison Syndrome
Mutation and non functioning PERK gene
What are the symptoms of Walcott Rallison Syndrome
Severe neonatal onset diabetes, epiphyseal dysplasia, osteoporosis and growth retardation
How is alzheimers related to eIF2 phosphorylation
misfolded protein causes phosphorylation of eIF2 shutting down translation, the misfolded proteins can not be fixed which leads to continued phosphorylation of eIF2 shutting down translation in the cell for the long term
PERK knockout models, inhibition models or over expression of phosphatases shows what promise
reduced severity of disease
What effect does phosphorylation have on 4EBP
Phosphorylation of 4EBP causes release of eIF4E which causes increased translation
What is the function of PERK kinase
PERK Kinase is activated in response to unfolded protein, PERK phosphorylated eIF2 stopping it from participate in translation initiation and translation is shut down
How is miRNA different from siRNA, how is it similar?
Difference: miRNA targets the RNA induced silencing complex to repress translation; siRNA targets the RISC to degrade mRNA.
Similar: Both are used to silence genes and stop expression
miRNA vs siRNA - which is normal, which is therapuetic
miRNA- natural
siRNA - therapeutic
