Translation

Question 1

T/F: knowing the amino acid sequence of a protein, the sequence of the gene can be predicted

Answer 1

FALSE: because of redundancy in genetic code

code is also non-ambiguous

Question 2

what is the specialized nucleotide of the 5’ cap which is necessary for binding of initiation factors for translation?

Answer 2

7-methyl-guanosine

Question 3

what is the start codon in eukaryotes

what are the stop codons

Answer 3

START: AUG - Methionine

STOP: UGA, UAA, UAG
[u go away, u are annoying, u are gone]

Question 4

codon-anticodon interactions are ____

Answer 4

antiparallel

Question 5

these enzymes catalyze charging of tRNA

Answer 5

aminoacyl-tRNA synthetases

REQUIRES ATP

includes proofreading before AND after —> high fidelity process

Question 6

what are the subunit sizes of eukaryotic and prokaryotic ribosomes

Answer 6

eukaryotic - 40S (small) + 60S (large) = 80S

prokaryotic - 30S (small) + 50S (large) = 70S

Question 7

where does the peptidyl transfer activity come from in translation?

Answer 7

rRNA catalyzes peptide bond formation —> ribosome is a ribozyme

Question 8

what are the 3 sites of tRNA binding

Answer 8

A (aminoacyl) - acceptor
P (peptidyl) - peptide chain is growing
E (exit) - empty (uncharged) tRNA is released

Question 9

what are the 3 basic steps of translation initiation (eukaryotic)

Answer 9

1. PIC (pre-initiation complex) binds mRNA cap complex. PIC includes Met, eIF2, GTP, and initiation tRNA (recognizes AUG)
2. scanning for first AUG codon
3. large subunit recruitment (GTP hydrolysis and release of eIF2)

Question 10

what are the 3 basic steps of elongation in translation (eukaryotic)

Answer 10

1. deliver tRNA to A site via eEF2 (proofreading occurs before and after), GTP hydrolysis follows
2. peptidyl transfer / peptide bond formation (via ribozyme)
3. translocation (grows N —> C terminal) with GTP-bound eEF2

Question 11

what causes translation termination (eukaryotic)

Answer 11

eRF1 (eukaryotic releasing factor 1) catalyzes hydrolysis of completed peptide

requires GTP hydrolysis

Question 12

polysome

Answer 12

large mRNA/multiple ribosome complex

multiple ribosomes can be translating single mRNA molecule simultaneously

Question 13

match:
eukaryotic and bacterial translation
with
polycistronic and monocistronic

Answer 13

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)

Question 14

what do aminoglycosides (streptomycin) and tetracyclines (doxycycline) target?

Answer 14

30S bacterial ribosomal subunit (the decoding site)

Question 15

what do macrolides (erythromycin) target?

Answer 15

50S bacterial ribosomal subunit (peptide bond formation site)

Question 16

miRNAs (non-coding) base pair with RNA sequences typically present in the _____

Answer 16

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]

Question 17

Ferritin is a protein that stores excess iron. Its translation is regulated by cellular iron status. Describe this process

Answer 17

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

Question 18

when are premature stop codons biologically useful?

Answer 18

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

Question 19

how does HIV-1 take advantage of programmed ribosomal frame shifting in translation?

Answer 19

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”)

Question 20

how does Polio mRNA bypass cap-dependent translation in host cells?

Answer 20

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

Question 21

describe the cellular pathogenesis of corynebacterium diphtheriae

bonus: how does it present?

Answer 21

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

Question 22

azithromycin belongs to the macrolide class of antibiotics - therefore, what does it target?

Answer 22

macrolide antibiotics target bacterial 50S ribosomal subunit

Question 23

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’

Answer 23

5’-AUG-3’ (methionine) corresponds to
5’-CAU-3’ because codon-anticodon alignment is antiparallel (have to read it backwards)

Question 24

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?

Answer 24

C. Diphtheria bacteria - produces toxin that ADP-ribosylates/inactivates eEF2 needed for ribosome translocation

in summary, Diphtheria toxin halts elongation

Question 25

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

Answer 25

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