Unit 6: Genetic material and molecular mechanisms of gene expression - Practice Quiz

1 Which sugar is present in DNA?

2 Which type of RNA carries genetic information from DNA to the ribosome?

3 What are the three basic components of a DNA nucleotide?

4 How are the two strands of a DNA double helix oriented?

5 Which base pairs with adenine in double-stranded DNA?

6 DNA replication is described as semiconservative because each new DNA molecule contains:

7 Which enzyme unwinds the DNA double helix during replication?

8 Where does protein synthesis occur in a cell?

9 Which type of RNA brings amino acids to the ribosome?

10 What is transcription?

11 Which enzyme synthesizes RNA during transcription?

12 Which codon usually begins translation?

13 What is a codon?

14 Which statement best defines a gene?

15 Which region of a gene commonly provides a binding site for RNA polymerase?

16 Which regions generally remain in mature eukaryotic mRNA after splicing?

17 What is the main function of a gene?

18 According to the central dogma, genetic information usually flows in which direction?

19 What is an operon?

20 In a typical operon, where does a repressor protein bind to block transcription?

21 A DNA segment containing alternating guanine and cytosine bases is placed under high-salt conditions. Which DNA conformation is this segment most likely to adopt?

22 A mutation prevents a small nuclear RNA from binding to pre-mRNA. Which process is most directly affected?

23 Bacteria containing DNA labeled with heavy nitrogen are transferred to light-nitrogen medium. After two rounds of semiconservative replication, what DNA molecules are expected?

24 A drug inhibits DNA ligase during bacterial DNA replication. Which molecular consequence is most likely?

25 A human cell line lacks functional telomerase but continues dividing. What change is most likely after many cell divisions?

26 A coding sequence mutation changes the mRNA codon 5′-UAU-3′ to 5′-UAA-3′. What is the most likely effect on the protein?

27 An aminoacyl-tRNA synthetase incorrectly attaches valine to a tRNA whose anticodon recognizes an alanine codon. What will occur during translation?

28 An antibiotic specifically inhibits the peptidyl transferase center of the large ribosomal subunit. Which event is directly blocked?

29 A DNA template strand has the sequence 3′-TAC GGA TTT-5′. Which RNA sequence will be produced?

30 Why can translation begin before transcription is complete in bacteria but not normally in eukaryotic cells?

31 A mutation weakens the promoter of a gene but leaves its coding and termination sequences intact. Which result is most likely?

32 Two homozygous recessive mutants have the same visible phenotype. Their offspring have the wild-type phenotype. What does this complementation result indicate?

33 A single eukaryotic gene produces one protein in liver cells and a structurally different protein in muscle cells. Which mechanism best explains this observation?

34 A mutation destroys the 5′ splice site of an intron, and no alternative splice site is available. What is the most likely effect on the mature mRNA?

35 A mutation deletes a tissue-specific enhancer located several thousand base pairs upstream of a gene. Which outcome is most likely?

36 A metabolic pathway is arranged as precursor A → intermediate B → product C. A mutation in the enzyme converting B to C would most likely cause which pattern?

37 Under which conditions is transcription of the bacterial lac operon expected to be highest?

38 When tryptophan is abundant, how does attenuation regulate the bacterial trp operon?

39 A histone acetyltransferase is recruited to the promoter of a normally inactive eukaryotic gene. What is the most likely result?

40 A partial diploid bacterium has the genotype lacOᶜ lacZ⁺ / lacO⁺ lacZ⁻ and contains functional lacI. What occurs when lactose is absent?

41 A covalently closed 4200-bp DNA circle contains a 40-bp segment that changes from B-DNA, with 10.5 bp per right-handed turn, to Z-DNA, with 12 bp per left-handed turn. No strand break occurs. Approximately how must writhe change?

42 Purified bacterial RNase P RNA cleaves pre-tRNA slowly at high concentration, whereas addition of its protein subunit permits rapid cleavage under physiological ionic conditions. Which conclusion is best supported?

43 Cells with fully -labeled DNA are transferred to medium for two generations and then returned to medium for one generation. Assuming semiconservative replication, what DNA classes occur after the final generation?

44 A bacterial mutant replicates its circular chromosome to completion, but the two daughter chromosomes remain topologically interlinked and cannot segregate. Which enzyme is most directly defective?

45 An engineered telomerase uses the RNA template segment 3′-CAAUCC-5′ for repeat synthesis. Ignoring flanking alignment nucleotides, which DNA sequence will be added to the chromosome's 3′ end?

46 In E. coli, a replication error lies near a hemimethylated GATC site. Which change would most directly compromise methyl-directed mismatch repair by obscuring identification of the newly synthesized strand?

47 A mutant aminoacyl-tRNA synthetase attaches alanine to a tRNA whose anticodon normally recognizes phenylalanine codons. If the mischarged tRNA enters the ribosome, what is the most likely outcome?

48 After acute addition of a translation inhibitor, ribosomes already on mRNAs complete elongation and dissociate, while few new ribosomes load. Polysome profiles progressively shift from heavy polysomes toward monosomes. Which process is primarily inhibited?

49 Rifampicin is added to bacteria actively transcribing a long operon. Full-length transcripts continue to appear briefly, but production then stops. Which mechanism explains this pattern?

50 During spliceosomal pre-mRNA splicing, which nucleophile performs the first transesterification reaction?

51 A suppressor tRNA is engineered to recognize the amber stop codon 5′-UAG-3′. When the anticodon is written 5′ to 3′, which sequence is required for direct Watson–Crick pairing?

52 In a trpR deletion strain, the two consecutive tryptophan codons in the trp leader peptide are replaced by alanine codons. Alanine remains abundant. What happens to operon expression during tryptophan starvation?

53 Two recessive mutations produce the same phenotype. A diploid carrying one mutation on each homolog remains mutant, yet rare wild-type meiotic recombinants are recovered. What is the strongest interpretation?

54 Two recessive missense mutations mapped to the same gene unexpectedly restore near-normal function when present in trans, although neither allele functions alone. Which explanation best fits this intragenic complementation?

55 A candidate regulatory sequence is integrated with the same minimal promoter and reporter at one defined chromosomal locus. Which result most specifically supports classification of the sequence as an enhancer rather than a core promoter element?

56 A genomic substitution changes the invariant +1 guanine of an intron's 5′ splice site. The resulting mature mRNA lacks the entire upstream exon, while transcription initiation is unchanged. Which molecular interaction was directly disrupted?

57 A signaling pathway has the order ligand → receptor R → inhibition of repressor X → expression of gene G. An R null mutant cannot express G, an X null mutant expresses G constitutively, and the R X double null also expresses G constitutively. What does the double-mutant phenotype establish?

58 Consider the partial diploid E. coli genotype . What pattern of -galactosidase production is expected in the absence and presence of lactose?

59 A microRNA reduces expression of a reporter carrying a candidate 3′-UTR target site. A point mutation in the site's seed-complementary region abolishes repression. Which result would provide the strongest evidence for direct base pairing?

60 A CTCF-bound boundary lies between an enhancer and a normally insulated promoter. Acute CTCF degradation causes new enhancer–promoter contacts and ectopic transcription; restoring CTCF reverses both effects. Which inference is best supported?