Unit 6: Regulation of Gene Expression and Epigenetics - Practice Quiz

1 In the lac operon of E. coli, which molecule acts as the inducer that inactivates the repressor?

2 The lac operon is best described as which type of operon?

3 What is the primary role of the operator sequence in an operon?

4 A riboswitch is a regulatory element located in which type of molecule?

5 Riboswitches typically regulate gene expression by binding to which of the following?

6 The bacteriophage lambda switch controls the decision between which two life cycles?

7 Which protein is essential for maintaining the lysogenic state in bacteriophage lambda?

8 Which covalent modification of histones is most commonly associated with active gene transcription?

9 Which enzyme adds acetyl groups to histone proteins?

10 Removal of acetyl groups from histones by HDAC enzymes generally leads to what effect on transcription?

11 Nucleosome remodelling complexes use the energy from which molecule to reposition nucleosomes?

12 What is the main purpose of nucleosome remodelling?

13 In mammals, DNA methylation most commonly occurs on cytosine bases found in which context?

14 Heavy DNA methylation of a gene's promoter region usually results in what?

15 What does the abbreviation RISC stand for in RNA interference?

16 Which small RNA molecule is loaded into RISC to guide it to a complementary target mRNA?

17 Which enzyme cleaves long double-stranded RNA into short fragments during RNA interference?

18 Heterochromatin is best described as which state of chromatin?

19 Epigenetic changes are best described as changes that:

20 Which epigenetic change is commonly seen at the promoters of tumour suppressor genes in cancer cells?

21 In the lac operon, a strain carries a mutation in the operator () on the same DNA molecule as functional structural genes. What phenotype is expected for -galactosidase expression?

22 The trp operon is regulated by both repression and attenuation. When tryptophan levels are moderate but not saturating, what primarily fine-tunes transcription of the structural genes?

23 Catabolite repression ensures glucose is used before lactose. If a lac operon strain has a mutation abolishing CAP binding, what is the effect when only lactose is present?

24 A riboswitch controls gene expression by which of the following mechanisms?

25 In a transcription-terminating riboswitch, binding of the target metabolite typically favors formation of which structure?

26 In the lambda lysis/lysogeny switch, high levels of the cI repressor bound to and produce which outcome?

27 The lambda switch behaves like a genetic toggle because cI and Cro compete for the same operators. Why does DNA damage (SOS response) shift the switch toward lysis?

28 Acetylation of lysine residues on histone tails generally promotes transcription. What is the most direct biochemical reason?

29 A researcher finds a gene enriched for H3K9me3 (trimethylation of histone H3 lysine 9). What is the likely transcriptional state and reason?

30 ATP-dependent chromatin remodelling complexes (e.g., SWI/SNF) regulate transcription primarily by which action?

31 In mammals, DNA methylation typically occurs at which sequence context and has what usual effect on nearby promoters?

32 DNA methylation patterns are heritable through cell division. Which enzyme is chiefly responsible for maintaining methylation on the newly synthesized strand after replication?

33 During RISC-mediated silencing, which component of the complex directly base-pairs with target mRNA to guide cleavage?

34 Perfect complementarity between a small RNA and its mRNA target in RISC typically leads to which outcome, versus imperfect pairing?

35 Which enzyme processes long double-stranded RNA or pre-miRNA hairpins into ~21–23 nucleotide duplexes during RNA interference?

36 In the miRNA pathway, what is the correct order of processing from the primary transcript?

37 Heterochromatin silences genes in part through position-effect variegation. What best explains why a gene relocated near heterochromatin shows patchy (variegated) expression?

38 In fission yeast, RNAi machinery contributes to heterochromatin formation at centromeres. What is the connection between small RNAs and heterochromatin?

39 Studies of the agouti mouse show that maternal diet (e.g., methyl-donor supplementation) alters coat color and disease risk in offspring. What is the epigenetic basis of this effect?

40 A tumor cell shows loss of expression of a tumor-suppressor gene despite an intact coding sequence. Which epigenetic change most commonly explains this in cancer?

41 In the lac operon, a mutation in the operator () that abolishes repressor binding is combined in a partial diploid with a wild-type operon on an F' plasmid. The genotype is . In the absence of inducer, which enzymes are constitutively synthesized?

42 The trp operon uses attenuation. If a mutation changes the two adjacent tryptophan codons in the leader peptide to two adjacent histidine codons, what is the predicted effect on operon regulation?

43 Many riboswitches contain an aptamer and an expression platform. Consider a transcriptional "OFF" riboswitch that forms an intrinsic terminator when its ligand is bound. Which statement best explains the kinetic requirement for its function?

44 The glmS ribozyme-riboswitch is unusual among riboswitches. What distinguishes its mechanism of controlling gene expression upon ligand binding?

45 In the lambda lysis/lysogeny decision, the cooperative binding of CI repressor to and has a key regulatory consequence. What is it?

46 During prophage induction following DNA damage, RecA-mediated autocleavage of CI shifts the switch toward lysis. Why does loss of CI at specifically not need to occur first for the switch to flip?

47 Trimethylation of histone H3 lysine 4 (H3K4me3) and lysine 27 (H3K27me3) can co-occur at "bivalent" domains in embryonic stem cells. What is the functional significance of these bivalent domains?

48 The "histone code" hypothesis predicts combinatorial readout of modifications. A protein contains both a bromodomain and a chromodomain in tandem. What binding behavior would this predict?

49 Histone acetylation generally correlates with transcriptional activation. Beyond neutralizing lysine charge, which additional mechanism most directly contributes to this activation?

50 ATP-dependent chromatin remodelers of the SWI/SNF family and the ISWI family differ functionally. Which contrast is correct?

51 The histone variant H2A.Z is deposited at nucleosomes flanking promoters. Experiments show its incorporation can both activate and repress genes depending on context. Which best explains this dual role?

52 In mammals, DNA methylation is maintained through replication by DNMT1 acting on hemimethylated CpG sites. If DNMT1 were selectively inactivated in a dividing cell population, what pattern would be observed over successive divisions?

53 Methyl-CpG-binding domain proteins (e.g., MeCP2) link DNA methylation to transcriptional repression. Which mechanistic connection is most accurate?

54 The conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) by TET enzymes is a key step in active demethylation. What is the primary fate that ultimately restores unmethylated cytosine?

55 In the RISC complex, an Argonaute protein with catalytic "slicer" activity is required for one silencing outcome but dispensable for another. Which pairing is correct?

56 Guide-strand selection during RISC assembly is not random. Which thermodynamic rule predicts which strand of the siRNA duplex is retained as the guide?

57 In some organisms RNAi is amplified and spreads systemically. Which enzymatic activity is essential for signal amplification but absent in mammals, explaining the lack of robust systemic RNAi in mammals?

58 In S. pombe, RNAi contributes to heterochromatin formation at centromeric repeats. Which sequence of events correctly links RNAi to heterochromatin assembly?

59 Position-effect variegation (PEV) in Drosophila occurs when a gene is relocated near heterochromatin. What does the mosaic (variegated) expression pattern reveal about heterochromatin spreading?

60 Cancer genomes often display two seemingly opposite DNA methylation changes simultaneously. Which combination and consequence is correct?