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5.1 Prokaryotic Translation β Test 1
Q1. 'Synonymous codons' in the genetic code imply that:β A mutation at the third codon position may not change the protein
Q2. Initiator formylmethionine/methionine is distinguished from internal methionine by:β Initiation codon vs internal codon (and a special initiator tRNA + IFs)
Q3. The mRNA sequence recognised by the small ribosomal subunit in prokaryotes is the:β Shine-Dalgarno sequence
Q4. A 222-nucleotide mRNA encodes how many amino acids (allowing for the stop codon)?β 73
Q5. Codon-anticodon pairing occurs through:β Hydrogen bonds
Q6. Inteins are:β Internal protein segments excised post-translationally, with flanking exteins joined
Q7. The genetic code is best described as:β Triplet, commaless, (nearly) universal and degenerate
Q8. Translating 5'-AAC UAA CUA ACU AAC...-3' (repeating AACUAAC) in a cell-free system yields short peptides because:β Stop codons (UAA) recur in-frame, giving multiple very short peptides
Q9. Aminoacyl-tRNA synthetase recognition of the correct tRNA depends largely on:β The acceptor stem (and often the anticodon)
Q10. Isoleucyl-tRNA synthetase avoids mischarging valine by:β Proofreading/editing that hydrolyses the incorrectly activated/charged amino acid
Q11. An antibiotic that resembles the 3' end of a charged (aminoacyl) tRNA is:β Puromycin
Q12. Puromycin inhibits protein synthesis by:β Entering the A site as an aminoacyl-tRNA analogue and causing premature chain termination
Q13. The anticodon is an exposed unpaired triplet found in:β tRNA
Q14. The E. coli large (50S) subunit consists of:β 23S rRNA, 5S rRNA and ~34 proteins
Q15. The coding (sense) strand of dsDNA is:β Identical in sequence to the transcribed RNA (with T for U)
Q16. Degenerate codons:β Usually differ at the third base and can encode the same amino acid
Q17. Peptidyl transferase activity (peptide-bond formation) in prokaryotes resides in:β 23S rRNA (a ribozyme)
Q18. During prokaryotic termination, which statement about release factors is INCORRECT?β Free RF3 prefers GDP strongly over GTP
Q19. Some bacteria lacking glutaminyl-tRNA synthetase make Gln-tRNA^Gln by:β Charging tRNA^Gln with glutamate, then amidating it to glutamine on the tRNA
5.1 Prokaryotic Translation β Test 2
Q20. GTP is directly required for which step of protein synthesis?β Translocation (and factor-mediated steps)
Q21. If the genetic code used four bases per codon, the maximum number of distinct codons would be:β 256
Q22. Poly-U mRNA translated in vitro yields a polypeptide of:β Phenylalanine
Q23. The repeating mRNA 5'-CACACACA...-3' (no initiator needed) encodes:β One protein with an alternating sequence of two amino acids
Q24. In the trinucleotide synthesis with A:C = 1:4, the chance of forming CAA is approximately:β 3%
Q25. 'ORF' in an mRNA stands for:β Open Reading Frame
Q26. About the bacterial initiator fMet β which statements are true? (B) Deformylase removes the formyl group; (D) aminopeptidases often remove the N-terminal Met:β B and D
Q27. The initiating codon for protein synthesis is:β AUG
Q28. Prokaryotic molecular phylogenies are commonly built using the gene for:β 16S rRNA
Q29. Peptidyl transferase activity resides exclusively in the:β 23S rRNA (large-subunit rRNA)
Q30. Selenocysteine incorporation in E. coli occurs by:β Charging tRNA^Sec with serine, converting it to selenocysteine, then delivery by SelB at a UGA recoded by a SECIS element
Q31. Which protein is a guanine-nucleotide exchange factor in bacterial translation?β EF-Ts (recycles EF-Tu's GDPβGTP)
Q32. RNA molecules with catalytic activity are called:β Ribozymes
Q33. Which base in the first anticodon position can pair (wobble) with U in the third codon position?β Guanine or inosine
Q34. The start site of a prokaryotic mRNA is selected by the ribosome using:β 16S rRNA (via Shine-Dalgarno pairing)
Q35. Streptomycin blocks correct initiation in prokaryotes by acting on:β The 16S rRNA / 30S subunit
Q36. The anticodon is located in which loop of tRNA?β Loop II (anticodon loop)
Q37. The tRNA arm ending in the CCA sequence (where the amino acid attaches) is the:β Acceptor arm
5.1 Prokaryotic Translation β Test 3
Q38. The E. coli small (30S) subunit consists of:β 16S rRNA + ~21 proteins
Q39. The stop codon 'Ochre' is:β UAA
Q40. The stop codon 'Opal' (umber) is:β UGA
Q41. During eukaryotic translation, methionines other than the initiator are encoded by:β AUG (read by elongator Met-tRNA)
Q42. The codon UAA specifies:β Termination (stop)
Q43. Matching tRNA arms: acceptor arm has the CCA/amino-acid end; the D-arm has dihydrouridine; the TΞ¨C arm has pseudouridine; the anticodon arm reads the codon. Which is correctly paired?β D-arm β dihydrouridine
Q44. The reaction Amino acid + ATP + tRNA β aminoacyl-tRNA + AMP + PPi is catalysed by:β Aminoacyl-tRNA synthetase
Q45. Which is NOT an essential part of the translational machinery?β Endoplasmic reticulum
Q46. The genetic code is 'degenerate' because:β There are more codons than amino acids (multiple codons per amino acid)
Q47. The RNA most extensively modified (e.g. methylation, unusual bases) after synthesis is:β tRNA
Q48. The 5' leader nucleotides of a bacterial pre-tRNA are removed by:β RNase P
Q49. The prokaryotic translation pre-initiation (30S initiation) complex includes:β Initiation factors, mRNA, 30S subunit, fMet-tRNA and GTP
Q50. The intrinsic tRNA identity for synthetase recognition lies mainly in the:β Acceptor stem (and often the anticodon loop)
Q51. All tRNAs terminate at the 3' end in the sequence:β 3'-CCA (amino-acid attachment)
Q52. In eukaryotes, RNA polymerases I/II/III make rRNA/mRNA/tRNA respectively. The correct match is:β I-rRNA, II-mRNA, III-tRNA
Q53. Prokaryotic protein synthesis can be inhibited by:β Puromycin
Q54. tRNA (the 'adaptor') was first proposed/discovered in work associated with:β Paul Zamecnik (and Hoagland)
Q55. The minimum number of high-energy phosphate bonds used to form ONE peptide bond is about:β Four
5.1 Prokaryotic Translation β Test 4
Q56. Translating the transcript of DNA 3'-AAGTACTCT-5' (template) gives which tripeptide?β Phe-Met-Arg
Q57. Which ribosomal RNA is a ribozyme acting as peptidyl transferase?β Peptidyl transferase centre (23S/28S rRNA)
Q58. Which acts as peptidyl transferase?β 23S rRNA in prokaryotes (and 28S in eukaryotes)
Q59. Which codon can be recoded to specify an amino acid (e.g. selenocysteine) in special contexts?β UGA
Q60. Which elongation factor is the translocase?β EF-G (and its eukaryotic counterpart eEF2)
Q61. Which RNA has the highest percentage of modified bases?β tRNA
Q62. Which statement describes the wobble rules correctly?β The third codon-anticodon base pairing is relaxed/flexible
Q63. Which statement is correct?β A stop codon has no corresponding tRNA
Q64. Which RNA class characteristically contains unusual purines and pyrimidines?β tRNA
Q65. Which nucleotide is required for the elongation stage of E. coli translation?β GTP
Q66. Which ribosomal RNA subunit (by sedimentation) is common to both prokaryotes and eukaryotes?β 5S rRNA
Q67. Which statement is NOT correct?β Both DNA and RNA are synthesised 5'β3'
Q68. Which enzyme recognises a specific amino acid AND its cognate tRNA?β Aminoacyl-tRNA synthetase
Q69. How many conformational (ratchet) changes coupled to GTP hydrolysis occur per elongation cycle?β Two (EF-Tu delivery and EF-G translocation)
Q70. The number of high-energy phosphates consumed to ADD one amino acid (after the first) is about:β 4
Q71. Methionyl-tRNA used to INITIATE protein synthesis is found in:β Eukaryotic cytoplasmic ribosomes (Met-tRNAi, unformylated)
Q72. EF-G requires which nucleotide for translocase activity?β GTP
Q73. The genetic code being 'commaless' means:β There are no gaps/punctuation between codons; they are read consecutively