Bacterial Transcription & Translation: Key Concepts & Mutations

1. Mutation in σ70 preventing -10 recognition but still binding RNAP causes what?

C — Housekeeping transcription drops because -10 recognition is essential.

2. Weak -10 region but optimal -35 causes what?

C — Promoter recognition & initiation decrease.

3. Delete Shine-Dalgarno but keep AUG: what happens?

B — Ribosome initiation becomes inefficient.

4. Why are transcription & translation coupled in bacteria?

B — No nucleus; both in cytoplasm.

5. Mutation in β' lowering promoter affinity effect?

A — Initiation decreases; elongation unchanged.

6. Loss of NusA binding causes what?

B — Impaired rho-independent termination.

7. Which disrupts rho-dependent termination?

C — Rho can't bind rut site.

8. Sigma replaced with non-releasing DNA binder causes what?

B — RNAP stuck; can't clear promoter.

9. Adding CTD to bacterial RNAP changes little because?

B — Bacteria lack CTD-dependent machinery.

10. Increase repressor concentration causes what?

A — Lowers operon transcription.

11. Strong promoter with no operator leads to what?

B — High, unregulated transcription.

12. LacI can't bind allolactose but binds operator: effect?

B — Always repressed.

13. Operator mutation preventing LacI binding: effect?

A — Constitutive expression.

14. When do repression & attenuation both strongly act?

C — Tryptophan abundant.

15. Mutate Trp codons in leader to Ala: effect?

B — Attenuation strengthens permanently.

16. Gene moved out of operon to solo promoter: what is lost?

B — Coordinated expression.

17. Loss of synthetase proofreading causes what?

A — Miscoded amino acids.

18. EF-Tu can't hydrolyze GTP: blocked step?

C — Release of EF-Tu & tRNA accommodation.

19. tRNA that reads UAG: effect?

B — Readthrough of stop codons → longer proteins.

20. What drives ribosome movement?

B — GTP hydrolysis by EF-G.

21. Reduce 16S SD complementarity causes what?

B — Defective initiation.

22. Feature of initiator tRNAfMet?

C — Recognized by IF-2 for P-site loading.

23. Small molecule that removes repressor from operator?

B — Inducer.

24. Converting repressible to inducible requires?

B — Default ON unless effector present.

25. Polycistronic mRNA in eukaryote: translation pattern?

B — Only first ORF translated.

26. Mutate -10 element: effect?

B — Impaired RNAP binding/open complex.

27. Overlapping σ70 & σ32 promoters advantage?

A — Expression under normal & heat shock.

28. Very weak -35/-10: compensation?

A — Increase RNAP holoenzyme levels.

29. Upstream activator-binding site resembles what in eukaryotes?

B — Enhancer activation.

30. 5'UTR hairpin blocking SD melts at heat: what is it?

C — RNA thermometer.

31. Leader peptide cannot translate: effect on attenuation?

A — Attenuation lost → full transcription.

32. Block charging of Trp tRNA: effect on trp operon?

B — Strong expression (stalling).

33. Operon activated only when activator + small molecule binds: type?

C — Positively inducible.

34. Delete terminator: immediate effect?

B — Readthrough transcription.

35. Physical separation of transcription & translation disrupts?

B — Attenuation.

36. Show mRNA is polycistronic by?

B — One promoter controls multiple proteins.

37. Ribosome can't bind RF1: which stop codon fails?

D — UAA & UAG.

38. Remove 3' CCA on tRNAs: effect?

A — No amino acid charging.

39. Eukaryotic intron-containing gene in bacteria: fate?

B — Transcribed but untranslated.

40. Block first phosphodiester bond: what accumulates?

D — Tiny abortive products (2-9 nt).

41. Strengthen poly-U tract: effect?

B — Stronger intrinsic termination.

42. Add weak upstream promoter lacking operator: effect?

B — Low-level expression even when repressed.

43. Activator loses DNA binding: effect?

B — Decreased transcription.

44. Riboswitch stabilizing terminator when ligand binds is?

B — Transcription termination control.

45. Loss of IF-3 binding: what happens?

B — Premature 30S-50S joining.

46. sRNA blocking SD sequence is what type of regulation?

B — Post-transcriptional translational control.

47. Positively repressible operon max expression when?

B — Low corepressor.

48. Delete alternative sigma factor (σE): result?

B — No expression under stress.

49. Promoter with higher RNAP affinity but same operator: effect?

A — Higher basal transcription.

50. mRNA unstable unless translated: why?

B — Prevent waste on unusable transcripts.