Gene Regulation and Epigenetics Practice Questions
40 free Gene Regulation and Epigenetics practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Gene regulation refers to the control of:
- A DNA replication timing
- B Protein degradation rates
- C Gene expression levels
- D Chromosome copy number
Correct answer: Gene expression levels
Gene regulation controls when, where, and at what level a gene is expressed. Mechanisms include transcriptional, post-transcriptional, translational, and post-translational regulation, ensuring each cell type produces only the proteins appropriate for its role.
An operon is best defined as:
- A A single gene with its own promoter
- B A set of co-regulated genes
- C A trans-acting regulatory protein
- D A eukaryotic chromosome domain
Correct answer: A set of co-regulated genes
An operon is a unit of gene expression in prokaryotes consisting of two or more functionally related structural genes transcribed as a single mRNA, controlled by a shared promoter and operator. The lac and trp operons are classic examples.
The lac operon is an example of a:
- A Repressible operon
- B Constitutive operon
- C Inducible operon system
- D Eukaryotic operon
Correct answer: Inducible operon system
The lac operon is an inducible system: it is normally repressed by the lac repressor and switched on only when lactose (converted to allolactose) is present. This allows the bacterium to express the lactose-metabolizing enzymes only when the substrate is available.
In the lac operon, the operator functions as a:
- A A binding site for RNA polymerase
- B A structural gene region
- C A binding site for the repressor
- D An enhancer-like regulatory element
Correct answer: A binding site for the repressor
The operator is a short DNA sequence located between the promoter and the structural genes of an operon. The repressor protein binds to the operator and physically blocks RNA polymerase from transcribing the downstream genes.
Which molecule acts as the inducer of the lac operon?
- A Glucose
- B Lactose itself
- C Allolactose
- D Galactose
Correct answer: Allolactose
Although lactose is the substrate, the actual inducer of the lac operon is allolactose — an isomer formed from lactose by the low-level activity of beta-galactosidase. Allolactose binds to the lac repressor, causing a conformational change that releases it from the operator.
The trp operon is classified as a:
- A Inducible operon
- B Constitutive operon
- C Repressible operon
- D Enhancer-dependent operon
Correct answer: Repressible operon
The trp operon is repressible: it is active by default (transcribed when tryptophan is scarce) and turned off when tryptophan levels are high. Tryptophan binds to the inactive aporepressor, converting it into an active repressor that blocks the operator.
In the trp operon, high levels of tryptophan result in:
- A Activation of transcription
- B Increased binding of RNA polymerase
- C Repressor binding and transcription block
- D Mutation of structural genes
Correct answer: Repressor binding and transcription block
When intracellular tryptophan is abundant, it acts as a corepressor by binding to the trp aporepressor. The tryptophan-repressor complex then binds the operator, blocking RNA polymerase access and halting transcription of the trp biosynthetic genes.
Which component of an operon contains the coding sequences for enzymes?
- A Promoter sequence
- B Operator sequence
- C Structural genes
- D Regulatory gene
Correct answer: Structural genes
Structural genes encode the proteins (typically enzymes) involved in a metabolic pathway. They are transcribed together as a single polycistronic mRNA in an operon.
Catabolite repression in the lac operon is mediated by:
- A Lac repressor protein alone
- B Low glucose levels only
- C cAMP and CAP complex
- D Operator site mutation
Correct answer: cAMP and CAP complex
Catabolite repression requires the cAMP-CAP (catabolite activator protein) complex, which forms when glucose is scarce and cAMP levels are high. This complex binds the CAP site and enhances transcription of the lac operon.
Epigenetics refers to heritable changes in gene expression that occur without changes in:
- A Protein tertiary structure
- B RNA nucleotide sequence
- C DNA nucleotide sequence
- D Chromosome copy number
Correct answer: DNA nucleotide sequence
Epigenetic changes alter gene expression without modifying the underlying DNA nucleotide sequence. These heritable modifications, such as DNA methylation and histone acetylation, can be passed through cell divisions.
DNA methylation typically leads to:
- A Increased gene expression
- B Transcriptional gene silencing
- C Accelerated DNA replication
- D Increased protein synthesis
Correct answer: Transcriptional gene silencing
DNA methylation typically represses gene expression by preventing transcription factor binding and recruiting repressor proteins. Methylation at CpG sites is a common mechanism of transcriptional gene silencing.
Which base is commonly methylated in eukaryotic DNA?
- A Adenine base
- B Guanine base
- C Cytosine
- D Thymine base
Correct answer: Cytosine
Cytosine is the primary base methylated in eukaryotic DNA, most commonly at CpG dinucleotides. 5-methylcytosine at these sites plays a key role in gene silencing and epigenetic inheritance.
Histone acetylation generally results in:
- A Condensation of chromatin fibers
- B Stable repression of target genes
- C Chromatin relaxation and transcription
- D Direct methylation of DNA bases
Correct answer: Chromatin relaxation and transcription
Histone acetylation neutralizes the positive charge on lysine residues, reducing histone-DNA interactions. This loosens chromatin structure (euchromatin) and promotes access by transcription factors, activating gene expression.
Which enzyme is responsible for histone acetylation?
- A DNA methyltransferase enzyme
- B Histone deacetylase enzyme
- C Histone acetyltransferase
- D RNA polymerase enzyme
Correct answer: Histone acetyltransferase
Histone acetyltransferases (HATs) transfer acetyl groups from acetyl-CoA to lysine residues on histone tails. This modification is associated with open chromatin and active transcription.
Heterochromatin is generally associated with:
- A Elevated gene expression levels
- B Transcriptional inactivity
- C Active regulatory enhancers
- D Rapid mRNA processing
Correct answer: Transcriptional inactivity
Heterochromatin is densely packed, making DNA inaccessible to transcription machinery. It is generally transcriptionally inactive and often contains repetitive sequences such as centromeric and telomeric DNA.
Euchromatin differs from heterochromatin because it is:
- A Densely packed and compact
- B Transcriptionally silent chromatin
- C Loosely packed and transcriptionally active
- D Restricted to prokaryotic genomes
Correct answer: Loosely packed and transcriptionally active
Euchromatin is loosely packed, allowing transcription factors and RNA polymerase to access the DNA. Unlike heterochromatin, it is transcriptionally active and contains most of the expressed protein-coding genes.
Which epigenetic modification can be reversed?
- A DNA point mutation
- B Chromosomal deletion
- C Histone modification
- D Gene copy duplication
Correct answer: Histone modification
Histone modifications such as acetylation and methylation are dynamic and enzymatically reversible. This reversibility allows cells to flexibly regulate gene expression in response to developmental or environmental signals.
RNA interference regulates gene expression by:
- A Promoting DNA replication
- B Blocking transcription initiation
- C Silencing mRNA via degradation or translational block
- D Remodeling histone structure
Correct answer: Silencing mRNA via degradation or translational block
RNA interference uses small RNAs (siRNA or miRNA) to guide the RISC complex to complementary mRNA sequences. RISC then either degrades the mRNA or stalls its translation, reducing protein output.
Which small RNA molecule is involved in gene silencing?
- A tRNA
- B rRNA
- C siRNA
- D hnRNA
Correct answer: siRNA
Small interfering RNA (siRNA) is loaded into the RNA-induced silencing complex (RISC), which uses the siRNA as a guide to cleave or suppress complementary mRNA targets, resulting in post-transcriptional gene silencing.
A key difference between prokaryotic and eukaryotic gene regulation is that eukaryotes:
- A Use operons as their primary regulatory strategy
- B Lack all transcription factors
- C Use epigenetic mechanisms
- D Regulate only metabolic genes
Correct answer: Use epigenetic mechanisms
Eukaryotic gene regulation relies heavily on epigenetic mechanisms such as DNA methylation and histone modification. While prokaryotes primarily use operon-based transcriptional control, eukaryotes add these heritable chromatin-level layers of regulation.
In the 'lac operon' of E. coli, what occurs when both glucose and lactose are present in the medium?
- A The operon is transcribed at a very low (basal) level
- B The operon is fully induced at a high rate
- C The repressor remains bound to the operator
- D The CAP-cAMP complex binds very strongly to the lac promoter region
Correct answer: The operon is transcribed at a very low (basal) level
When glucose is present, cAMP levels are low, preventing the CAP-cAMP complex from binding to the promoter. Even if lactose is present to remove the repressor, transcription remains at a low basal level due to catabolite repression.
Which specific protein is produced by the 'lacI' gene and regulates the lac operon?
- A Beta-galactosidase
- B Permease
- C Transacetylase
- D Lac repressor
Correct answer: Lac repressor
The lacI gene is a regulatory gene located outside the operon. It constitutively produces the lac repressor protein, which binds to the operator to block transcription in the absence of an inducer.
The 'Attenuation' mechanism in the 'trp operon' is possible in prokaryotes because:
- A Transcription and translation are coupled in the cytoplasm
- B Prokaryotes have a nucleus that separates processes
- C The trp operon functions as an inducible genetic regulatory system
- D Introns are spliced out of the mRNA before translation can begin
Correct answer: Transcription and translation are coupled in the cytoplasm
Attenuation relies on the ribosome's position on the mRNA while it is still being transcribed. Since prokaryotes lack a nuclear membrane, translation begins before transcription is finished, allowing the leader sequence to form different secondary structures.
Which epigenetic modification involves the addition of a methyl group to the 5th carbon of a cytosine residue, typically within CpG islands?
- A DNA Methylation
- B Histone Tail Methylation
- C Acetylation
- D Phosphorylation
Correct answer: DNA Methylation
DNA methylation occurs at CpG sites (Cytosine-phosphate-Guanine). High levels of DNA methylation in promoter regions are generally associated with long-term gene silencing.
In eukaryotic gene regulation, 'Enhancers' are DNA sequences that:
- A Can act at a distance to increase the rate of transcription
- B Are typically located just upstream of the promoter
- C Function mainly as binding sites for transcriptional repressor proteins
- D Are located within the protein-coding exons of a gene, not introns
Correct answer: Can act at a distance to increase the rate of transcription
Enhancers are distal regulatory elements. They can be thousands of base pairs away from the promoter, either upstream or downstream, and function by looping the DNA to interact with the transcription initiation complex.
What is the role of 'Histone Deacetylases' (HDACs) in chromatin remodeling?
- A They add acetyl groups to relax chromatin
- B They remove acetyl groups, condensing chromatin
- C They methylate DNA to silence gene expression
- D They help the ribosome bind to the mRNA transcript
Correct answer: They remove acetyl groups, condensing chromatin
HDACs remove acetyl groups from histone tails, restoring the positive charge on lysine residues. This increases the attraction between histones and the negatively charged DNA, leading to a closed chromatin structure (heterochromatin).
The 'Galactose (GAL) system' in yeast is regulated by GAL4. When galactose is absent, which protein binds to GAL4 to inhibit its activation domain?
- A GAL3
- B GAL80
- C TBP
- D TFIID
Correct answer: GAL80
GAL80 acts as a repressor by binding to the activation domain of the GAL4 transcription factor. When galactose is present, it interacts with GAL3 to remove GAL80 from GAL4.
Which of the following describes 'Genomic Imprinting'?
- A The mutation of a gene due to environmental stress
- B The expression of a gene depends on which parent it was inherited from
- C The conversion of euchromatin into heterochromatin during heat shock
- D The random inactivation of one X chromosome in females
Correct answer: The expression of a gene depends on which parent it was inherited from
Imprinting is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner. It is maintained by epigenetic marks established during gametogenesis.
In the 'trp operon', if the level of tryptophan in the cell is very low, what happens to the 'Repressor' protein?
- A It binds to the operator and blocks transcription
- B It remains inactive and does not bind to the operator
- C It binds to the promoter to recruit RNA polymerase
- D It is degraded by proteasomes
Correct answer: It remains inactive and does not bind to the operator
The trp repressor is an aporepressor; it requires tryptophan (the corepressor) to change its shape and bind to the operator. Without tryptophan, the operator is free, and the operon is 'on'.
Which RNA molecule is processed by the enzyme 'Dicer' into short fragments to facilitate gene silencing via the RISC complex?
- A Messenger RNA (mRNA)
- B Transfer RNA (tRNA)
- C MicroRNA (miRNA)
- D Ribosomal RNA (rRNA)
Correct answer: MicroRNA (miRNA)
miRNAs are transcribed as primary transcripts (pri-miRNA) and eventually processed by Dicer in the cytoplasm into mature ~22 nucleotide duplexes that guide the RISC complex to target mRNAs.
What is the function of the 'TATA box' in eukaryotic promoters?
- A It acts as a termination signal for RNA polymerase
- B It is the binding site for transcription factor TFIID
- C It encodes the start codon for the protein product
- D It is the site where the gene repressor binds
Correct answer: It is the binding site for transcription factor TFIID
The TATA box is a core promoter element. It is recognized by the TATA-binding protein (TBP), a subunit of TFIID, which helps position RNA polymerase II for transcription initiation.
The phenomenon where a single gene can produce multiple different protein isoforms is known as:
- A Gene duplication
- B Alternative splicing
- C Polyadenylation
- D RNA editing
Correct answer: Alternative splicing
Alternative splicing allows different combinations of exons to be joined together from a single pre-mRNA transcript, significantly increasing the diversity of the proteome in eukaryotes.
Which of the following is true regarding 'Barr Bodies'?
- A They are found in both males and females
- B They are regions of high transcriptional activity
- C They are only found in the germline cells
- D They are a condensed, inactivated X chromosome
Correct answer: They are a condensed, inactivated X chromosome
In female mammals, one X chromosome is randomly inactivated in every somatic cell to ensure dosage compensation. This inactivated chromosome becomes a dense mass of heterochromatin called a Barr body.
In the 'ara operon' of E. coli, the AraC protein functions as:
- A Only a transcriptional repressor
- B Only a transcriptional activator
- C Both an activator and a repressor
- D The enzyme that breaks down arabinose
Correct answer: Both an activator and a repressor
AraC is a dual-function regulator. In the absence of arabinose, it forms a DNA loop that represses the operon. In the presence of arabinose, it changes conformation to act as an activator.
Which type of control is exerted when a regulatory protein binds to DNA and stimulates the transcription of a gene?
- A Negative control
- B Constitutive control
- C Feedback inhibition
- D Positive control
Correct answer: Positive control
Positive control involves an activator protein that increases the affinity of RNA polymerase for the promoter, whereas negative control involves a repressor that blocks RNA polymerase.
The 'IPTG' (Isopropyl β-D-1-thiogalactopyranoside) is often used in laboratory settings as an inducer for the lac operon because:
- A It is a natural sugar found in dairy products
- B It binds to the promoter instead of the operator
- C It significantly increases E. coli growth rate
- D It cannot be metabolized, keeping its levels constant
Correct answer: It cannot be metabolized, keeping its levels constant
IPTG is a structural mimic of allolactose. Unlike allolactose, E. coli cannot break it down with beta-galactosidase, making it a 'gratuitous inducer' that keeps the operon 'on' throughout the experiment.
Epigenetic 'writer' enzymes are those that:
- A Recognize and bind to specific modifications
- B Remove chemical groups from histones or DNA
- C Add methyl or acetyl groups to DNA or histones
- D Repair damaged or mismatched DNA sequences
Correct answer: Add methyl or acetyl groups to DNA or histones
In epigenetic nomenclature, 'writers' add marks (e.g., Histone Acetyltransferases), 'erasers' remove them (e.g., Histone Deacetylases), and 'readers' interpret them by binding to them.
Which component of the RNA-induced silencing complex (RISC) is responsible for cleaving the target mRNA?
- A Dicer
- B Drosha
- C Argonaute
- D RNA Polymerase
Correct answer: Argonaute
The Argonaute (Ago) protein is the catalytic engine of the RISC complex. It uses the small RNA guide to find the complementary mRNA and uses its 'slicer' activity to degrade it.
In the absence of lactose, the lac repressor binds to the operator. The operator is a sequence located:
- A Downstream of the lacA gene
- B Inside the lacI repressor gene
- C Located on a different chromosome
- D Between the promoter and lacZ gene
Correct answer: Between the promoter and lacZ gene
The operator (lacO) is situated between the promoter (lacP) and the first structural gene (lacZ). When the repressor is bound here, it physically prevents RNA polymerase from moving into the structural genes.
Which term describes a cluster of genes under the control of a single promoter that are transcribed into a single polycistronic mRNA?
- A Operon
- B Regulon
- C Intron
- D Exon
Correct answer: Operon
An operon is the functional unit of genomic DNA in prokaryotes. It allows a set of genes with related functions to be regulated and expressed simultaneously.