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5.4 Translational Regulation โ Test 1
Q1. For uncapped (e.g. some viral) mRNAs, the ribosome initiates at the:โ Internal ribosome entry site (IRES)
Q2. Under stress, a kinase phosphorylates a translation initiation factor to shut down most protein synthesis. The target is:โ eIF2ฮฑ
Q3. During heat shock, cells shut down bulk translation but still make Hsps because:โ Cap-dependent translation drops while Hsp mRNAs use IRES/cap-independent initiation
Q4. A high polyribosome (polysome) fraction in a cell indicates:โ A high rate of protein synthesis (many ribosomes per mRNA)
Q5. Globin synthesis in the absence of heme is shut off by phosphorylation of:โ eIF2 (by the heme-regulated inhibitor, HRI)
Q6. siRNAs and miRNAs usually bind which region of target mRNAs during silencing?โ 3' UTR
Q7. Phosphorylation of eIF2ฮฑ (Ser51) leads to:โ Sequestration/inhibition of eIF2B (the GEF), lowering eIF2ยทGTP recycling
Q8. In yeast, eIF2ฮฑ phosphorylation paradoxically increases translation of mRNAs that have:โ Upstream ORFs (uORFs) preceding the main ORF (e.g. GCN4)
Q9. Circular (closed-loop) mRNA promotes efficient translation because:โ eIF4G and PABP bridge the 5' cap and 3' poly-A, aiding ribosome recycling/re-initiation
Q10. Tunicamycin blocks which process?โ N-linked glycosylation
Q11. Processing/modification of rRNA is guided by which small RNAs?โ snoRNA
Q12. Overexpression of the cap-binding protein eIF4E in cells tends to cause:โ Neoplastic (oncogenic) transformation
Q13. The kind of silencing mediated by miRNAs is mainly:โ Post-transcriptional (translational repression/mRNA decay)
Q14. A single miRNA typically regulates:โ Many different target mRNAs
Q15. Which RNA contains a region acting as a switch (ligand-sensing) to turn translation on/off?โ Riboswitch
Q16. The aptamer sequence that binds a small molecule is located in the:โ Riboswitch region of the mRNA
Q17. Where do siRNAs/miRNAs guide RISC to act on a target?โ Complementary sites usually in the mRNA 3' UTR
Q18. A single microRNA can target multiple transcripts and a single mRNA can be targeted by multiple miRNAs โ this describes:โ Combinatorial, many-to-many miRNA-target regulation
5.4 Translational Regulation โ Test 2
Q19. RNA interference is best described as:โ dsRNA cleaved by Dicer into siRNAs that guide sequence-specific silencing
Q20. Which statement about siRNA and miRNA is NOT true?โ Both usually silence the same loci they originate from
Q21. In VIGS/RNAi, what ultimately guides siRNA to degrade the target mRNA?โ The RNA-induced silencing complex (RISC)
Q22. RNAi of a gene-regulatory protein gave no transcriptome change. A plausible reason is:โ Any of these could explain it
Q23. To test whether an siRNA phenotype is on-target, the best controls are:โ Rescue with an siRNA-resistant (silent-site) cDNA, and use multiple independent siRNAs
Q24. Dicer is the enzyme that:โ Cleaves long dsRNA/pre-miRNA into ~21โ23 nt small RNAs
Q25. miRNA-based gene silencing is a type of:โ Post-transcriptional gene silencing
Q26. Which RNA molecules antagonize translation of target mRNAs?โ miRNA
Q27. A single microRNA being abundant at night and absent by day: which expectation is UNEXPECTED?โ Partially-matched targets are FREE of RISC at night
Q28. In eukaryotes, pre-miRNAs and most siRNA precursors are transcribed mainly by:โ RNA Pol II
Q29. Which RNAs are NOT transcribed by RNA Pol II?โ tRNA and 5S rRNA
Q30. The IRE (iron-response element) in an mRNA UTR is bound by IRP to:โ Regulate translation/stability in response to iron levels
Q31. mRNA half-life (stability) is strongly influenced by:โ Elements such as AU-rich elements (AREs) in the 3' UTR and the poly-A tail
Q32. Protein degradation targeting a protein for the proteasome usually requires:โ Polyubiquitination (the ubiquitin-proteasome pathway)
Q33. mRNA localization (e.g. to specific cell regions) is typically directed by signals in the:โ 3' UTR (zipcode elements)
Q34. Cap-independent translation is typically used when:โ Cap-dependent initiation is impaired (stress, mitosis, viral infection) via IRES elements
Q35. The 4E-BP proteins regulate translation by:โ Binding eIF4E and blocking eIF4F assembly (until phosphorylated by mTOR)