Translation Flashcards
T/F: knowing the amino acid sequence of a protein, the sequence of the gene can be predicted
FALSE: because of redundancy in genetic code
code is also non-ambiguous
what is the specialized nucleotide of the 5’ cap which is necessary for binding of initiation factors for translation?
7-methyl-guanosine
what is the start codon in eukaryotes
what are the stop codons
START: AUG - Methionine
STOP: UGA, UAA, UAG
[u go away, u are annoying, u are gone]
codon-anticodon interactions are ____
antiparallel
these enzymes catalyze charging of tRNA
aminoacyl-tRNA synthetases
REQUIRES ATP
includes proofreading before AND after —> high fidelity process
what are the subunit sizes of eukaryotic and prokaryotic ribosomes
eukaryotic - 40S (small) + 60S (large) = 80S
prokaryotic - 30S (small) + 50S (large) = 70S
where does the peptidyl transfer activity come from in translation?
rRNA catalyzes peptide bond formation —> ribosome is a ribozyme
what are the 3 sites of tRNA binding
A (aminoacyl) - acceptor
P (peptidyl) - peptide chain is growing
E (exit) - empty (uncharged) tRNA is released
what are the 3 basic steps of translation initiation (eukaryotic)
- PIC (pre-initiation complex) binds mRNA cap complex. PIC includes Met, eIF2, GTP, and initiation tRNA (recognizes AUG)
- scanning for first AUG codon
- large subunit recruitment (GTP hydrolysis and release of eIF2)
what are the 3 basic steps of elongation in translation (eukaryotic)
- deliver tRNA to A site via eEF2 (proofreading occurs before and after), GTP hydrolysis follows
- peptidyl transfer / peptide bond formation (via ribozyme)
- translocation (grows N —> C terminal) with GTP-bound eEF2
what causes translation termination (eukaryotic)
eRF1 (eukaryotic releasing factor 1) catalyzes hydrolysis of completed peptide
requires GTP hydrolysis
polysome
large mRNA/multiple ribosome complex
multiple ribosomes can be translating single mRNA molecule simultaneously
match:
eukaryotic and bacterial translation
with
polycistronic and monocistronic
eukaryotic is monocistronic - 1 coding region (aka open reading frame, ORF, or cistron)
prokaryotic is polycistronic - multiple coding regions (ORF, cistron), multiple messages per transcript
each prokaryotic cistron has ribosome-binding site - Shine-Dalgarno sequence - located upstream of AUG (directly base pairs to rRNA)
what do aminoglycosides (streptomycin) and tetracyclines (doxycycline) target?
30S bacterial ribosomal subunit (the decoding site)
what do macrolides (erythromycin) target?
50S bacterial ribosomal subunit (peptide bond formation site)
miRNAs (non-coding) base pair with RNA sequences typically present in the _____
3’-UTR of target mRNAs to inhibit translation - can cause translational repression or mRNA degradation
use RISC (RNA-induced silencing complex)
[can measure circulating miRNA as biomarker of disease]
Ferritin is a protein that stores excess iron. Its translation is regulated by cellular iron status. Describe this process
IRE (iron response element) in ferritin mRNA 5’-UTR is bound by IRP (iron regulatory protein) to lower production of Ferritin when iron is low
iron can bind IRP when levels are high, disinhibiting Ferritin production
when are premature stop codons biologically useful?
when two tissues express the same gene but one uses a shorter form
ex: APOB gene in liver and intestine. Intestine requires a shorter form, so mRNA is edited to introduce premature stop codon
how does HIV-1 take advantage of programmed ribosomal frame shifting in translation?
allows virus to generate 1+ protein from single mRNA
pseudoknots (secondary mRNA loops) stall ribosome movement - induces higher propensity to shift frame, esp in repetitive sequences (“slippery”)
how does Polio mRNA bypass cap-dependent translation in host cells?
mRNA contains internal ribosome entry site (IRES) that allows cap-independent translation or viral proteins —> directly recruits 40S subunit
viral proteases cleave eIF4G (initiation factor), which halts host mRNA transcription and diverts machinery to viral RNA
describe the cellular pathogenesis of corynebacterium diphtheriae
bonus: how does it present?
diphtheria toxin inactivates eEF2, by transferring ADP-ribose from NAD to eEF2
presentation: soar throat, gray/white pseudo-membrane due to cell death. vaccine available as part of DTaP
azithromycin belongs to the macrolide class of antibiotics - therefore, what does it target?
macrolide antibiotics target bacterial 50S ribosomal subunit
the RNA codon for methionine is 5’-AUG-3’ - which of these is the anticodon sequence?
a. 5’ - UAC - 3’
b. 5’ - TAC - 3’
c. 5’ - CAU - 3’
d. 5’ - CAT - 3’
5’-AUG-3’ (methionine) corresponds to
5’-CAU-3’ because codon-anticodon alignment is antiparallel (have to read it backwards)
Pt is a 7yo F presenting with chills, N/V, sore throat. PE notes grayish-colored membrane near the tonsils.
What bacteria is this infection caused by, and what is the effect of its toxin?
C. Diphtheria bacteria - produces toxin that ADP-ribosylates/inactivates eEF2 needed for ribosome translocation
in summary, Diphtheria toxin halts elongation
Which of the following enables polio virus to translate viral proteins in a cap-independent manner?
a. programmed ribosomal frame shifting
b. internal ribosomal entry site
c. ADP ribosylation of eEF2
d. phosphorylation of eIF2
e. RNA editing
f. miRNA
g. IRE-IRP interaction
polio - uses internal ribosomal entry site (IRES) to translate in cap-independent manner
viral protease cleaves eIF4G needed to recruit 40S subunit —> host translation inhibited and resources diverted —> cleaved eIF4G binds viral IRES for direct recruitment of 40S subunit
