Translation LO Flashcards
what is the central dogma?
DNA to RNA to Protein
how many high-energy bonds are formed for each peptide bond?
4
True of False
the basic process of translation is highly conserved between all forms of life
True
what is the function of messenger RNA (mRNA)?
carries codons that code for the amino acid sequence of a protein
how many possible codons are there?
4^3= 64 possible codons
What is the start codon?
AUG
what are the “non-sense” or stop codons on RNA?
UGA
UAA
UAG
what is the function of transfer RNA (tRNA)?
“read” the message and deliver the right amino acid to the ribosome
what dictates the function of tRNA?
the three-dimensional folded structure
why can some tRNA’s recognize more than one codon?
wobble-pairing at the third location on the codon
what is the function of aminoacyl tRNA synthetases?
protein enzymes that put the right amino acid on the right tRNA
what is the function of the ribosome?
catalytic center for translation
what synthetase puts a valine on a val-tRNA?
valyl-tRNA synthetase
aminoacid-tRNA synthetase
what are the 2 subunits in prokaryotic ribosomes?
30S and 50S
what are the 2 subunits in eukaryotic ribosomes?
30S and 60S
which subunit contains the catalytic center?
the large subunit
what is another name for the catalytic center of a ribosome?
peptidyl transferase center (PTR)
what type of enzyme is a ribosome and why?
ribozyme because it uses RNA to perform catalysis
what is the function of initiating factors in translation?
bring ribosome to the message and assist in getting the machinery assembled
what is the function of elongation factors and their partners?
deliver tRNAs and move ribosome down the message
what is the function of termination/recycling factors?
end the process at stop codon, disassociate subunits so they can be used again
where is the amino acid attached on tRNA?
the acceptor stem
which portion of the tRNA reads the mRNA?
anticodon loop
what is the start codon and which amino acid does it code for?
AUG
methionine
what is the final assembled ribosome called in prokaryotes?
70S
what is the final assembled ribosome called in eukaryotes?
80S
how many tRNA binding sites does a ribosome have?
3
what are the 3 binding sites on a ribosome?
A- aminoacyl site
P - peptidyl site
E - exit site
what are the 4 phases of translation?
- initiation
- elongation
- termination
- ribosome recycling
which step in translation differs the most between eurkaryotes and prokaryotes?
initiation
what is the point of the initiation step?
assemble ribosome at start codon (AUG) with initiator methionine tRNA in P-site and next aa-tRNA in the A-site
what initiation factor proteins are used in prokaryotes to bind the 30S subunit?
IF1 and IF3
what is the function of IF2 in prokaryotes?
delivers special “initiator” formylmethionine tRNA to P-site to pair with AUG codon
what does GTP hydrolysis of IF2 lead to?
release of all initiation factors and binding of 50S subunit forming 70S ribosome
why does the ribosome in prokaryotes bind directly to the AUG codon?
Shine-Dalgarno sequence about 8 bp upstream from AUG codon
what initiation factor in eukaryotes binds the 7-methyl guanosine cap to the 5’ end of RNA?
4E
what does polycistronic mean?
mRNA can have many genes expressed on just one strand such as in prokaryotes (have many shine-dalgarno sites) (lac operon)
how is eukaryotic initiation different than prokaryotic initiation?
eukaryotic more complex, ribosome scans downstream to find AUG codon after small subunit binds and then large subunit can bind, prokaryotes bind directly to AUG codon
which step of translation is considered to have the most control and regulation?
initiation
what is elongation?
moving along the mRNA and making the encoded protein
where does the energy for peptide bond formation come from?
ATP used in tRNA charging
what moves the mRNA and tRNAs exactly one codon in the 3’ direction?
EF2 and GTP hydrolysis
what are the 4 high energy bonds expended to form a peptide bond?
- charge tRNA (2 ATP to AMP)
- deliver aa-tRNA to A site (1 GTP to GDP)
- translocation (1 GTP to GDP)
which factors bind to the stop codon and terminate the polypeptide synthesis?
release factors
what is a missense mutation?
mutation resulting in amino acid change
what is a silent mutation?
codon is changed but same amino acid is encoded (the mutation is in the wobble position)
what is a frame-shift mutation?
an addition or deletion of a nucleotide causes a shift in the reading frame
what is a non-sense mutation?
mutation resulting in a premature stop codon
what is a sense mutation?
mutation resulting in a removed stopped codon
what mutation is Hemoglobin Wayne a result of?
3’ terminal frameshift mutation
what mutation is Hemoglobin Constant Spring a result of?
Sense mutation (UAA stop to CAA Gln)+
what presentation do both Hemoglobin Wayne and Hemoglobin Constant Spring have?
chronic anemia
why can production of protein be slowed if a mutation gives rise to a “rare” codon?
because there are a limited number of tRNA for each amino acid
what determines the strength of expression of different AUG’s in eukaryotes?
Kozak Context
what is RNA editing and why is it significant?
transcribed RNA modified so that coding is affected. important because some proteins are tissue specific, can have 2 types of protein from 1 gene that is tissue specific (apoB)
transferrin
binds iron
transferrin receptor (TFR)
transports Fe into the cell
ferritin
sequesters excess FE
iron repsponse element (IRE)
RNA stem-loop structure found in mRNAs that can bind to IRPs
Irons Response Binding proteins (IRE-BPs) 1 and 2
bind FE and regulate expression of ferritin and TFR
under high Fe conditions, what is the relationship between IRE-BPs, Fe, and IRE RNA
IRE-BPs bound to Fe
IRE-BPs cannot bind to IRE RNA
under low Fe conditions what is the relationship between IRE-BPs, Fe, and IRE RNA?
IRE-BPs not bound to Fe
IRE-BPs can bind to IRE RNA
What happens to the level of transferrin receptor protein in low iron conditions?
protein level increases
what happens to the level of transferrin receptor protein in high iron conditions?
protein level decreases
what is the mechanism of transferrin receptor protein regulation?
in low iron situations, IRE-binding protein binds to IRE of mRNA protecting the mRNA strand from being degraded and thus synthesis continues (opposite in high iron situations)
what happens to ferritin levels in low iron concentrations?
decrease
what happens to ferritin levels in high iron concentrations?
increases
what is mechanism of ferritin regulation?
in low iron situations, IRE-BP binds to IRE thus inhibiting ferritin synthesis because IRE prior to start codon (opposite in high concentration)
what is cap-independent translation?
mRNA does not require cap to initiate synthesis, instead has internal ribosomal entry site (IRES) which can recruit the subunit
why is cap-independent translation important for viruses?
because virus can shut down cap-dependent translation by cleaving eIF4G in the eukaryotic cell but continue replicating its own RNA
how does mTOR regulate eIF4E?
mTOR can induce phosphorylation on the eIF4E-binding protein thus dissociating the binding protein from the initiating factor thus allowing translation to occur
what is the process of interferon signaling?
cell infected by virus, infected cell creates interferons which signals other cells to create anti-viral measures (eIF2 kinase), virus cannot proliferate in cells notified by initial infected translation machinery shut off
