Q.1 What is the primary function of a promoter in gene regulation?
To code for a protein
To bind RNA polymerase and initiate transcription
To terminate transcription
To splice introns
Explanation - Promoters are DNA sequences upstream of a gene where RNA polymerase binds to start transcription.
Correct answer is: To bind RNA polymerase and initiate transcription
Q.2 In the lac operon, which molecule acts as an inducer?
Allolactose
cAMP
Glucose
Lactose repressor
Explanation - Allolactose binds the lac repressor, causing it to release the operator and allowing transcription.
Correct answer is: Allolactose
Q.3 Which of the following best describes a transcription factor?
An enzyme that degrades mRNA
A protein that binds DNA to regulate transcription
A lipid that stabilizes membranes
A ribosomal RNA component
Explanation - Transcription factors are proteins that bind specific DNA sequences to increase or decrease transcription rates.
Correct answer is: A protein that binds DNA to regulate transcription
Q.4 What is the role of DNA methylation in gene regulation?
Enhances transcription by recruiting RNA polymerase
Silences gene expression by preventing transcription factor binding
Increases mRNA stability
Facilitates ribosome assembly
Explanation - Methyl groups added to cytosine residues often block transcription factor access, leading to gene silencing.
Correct answer is: Silences gene expression by preventing transcription factor binding
Q.5 Which of the following is a type of RNA that directly regulates gene expression by degrading target mRNAs?
tRNA
rRNA
microRNA (miRNA)
snRNA
Explanation - miRNAs bind complementary sequences in mRNAs, leading to degradation or translational repression.
Correct answer is: microRNA (miRNA)
Q.6 In eukaryotes, which DNA element can function at a great distance from the gene it regulates?
Operator
Promoter
Enhancer
Terminator
Explanation - Enhancers can be located kilobases away from the transcription start site and increase transcription efficiency.
Correct answer is: Enhancer
Q.7 What is the primary outcome when a repressor protein binds to an operator sequence?
Activation of transcription
Inhibition of transcription
Splicing of the pre‑mRNA
Translation initiation
Explanation - Binding of a repressor to the operator blocks RNA polymerase progression, preventing transcription.
Correct answer is: Inhibition of transcription
Q.8 Which of the following best describes the CRISPR‑Cas9 system in gene regulation?
It adds methyl groups to DNA promoters
It uses guide RNA to target specific DNA sequences for editing or repression
It degrades mRNA in the cytoplasm
It enhances ribosome binding to mRNA
Explanation - CRISPR‑Cas9 can be programmed with guide RNAs to bind specific genomic loci for cutting or transcriptional modulation.
Correct answer is: It uses guide RNA to target specific DNA sequences for editing or repression
Q.9 What is the function of the TATA box in eukaryotic promoters?
It signals termination of transcription
It binds the ribosome during translation
It positions RNA polymerase II for transcription initiation
It encodes a protein domain
Explanation - The TATA box is a core promoter element that helps recruit the transcription machinery.
Correct answer is: It positions RNA polymerase II for transcription initiation
Q.10 Which modification is commonly associated with active chromatin?
Histone deacetylation
DNA methylation
Histone acetylation
Histone methylation at H3K9
Explanation - Acetylation of histone tails reduces their positive charge, loosening DNA‑histone interaction and promoting transcription.
Correct answer is: Histone acetylation
Q.11 In the trp operon, the repressor is active when it is bound to:
cAMP
ATP
Tryptophan
Glucose
Explanation - Tryptophan acts as a corepressor, binding the trp repressor and enabling it to attach to the operator.
Correct answer is: Tryptophan
Q.12 Which of the following processes does NOT directly alter the DNA sequence but can affect gene expression?
Point mutation
DNA methylation
Insertion of a transposon
Deletion of an exon
Explanation - DNA methylation is an epigenetic modification that does not change the nucleotide sequence but influences transcription.
Correct answer is: DNA methylation
Q.13 What is the role of the sigma (σ) factor in bacterial transcription?
It terminates transcription
It unwinds DNA ahead of RNA polymerase
It guides RNA polymerase to specific promoters
It splices introns
Explanation - σ factor recognizes promoter elements and helps RNA polymerase initiate transcription at the correct site.
Correct answer is: It guides RNA polymerase to specific promoters
Q.14 Which type of RNA is directly involved in the splicing of pre‑mRNA?
snRNA
tRNA
rRNA
miRNA
Explanation - Small nuclear RNAs (snRNAs) form part of the spliceosome, which removes introns from pre‑mRNA.
Correct answer is: snRNA
Q.15 What is a common effect of histone H3 lysine 27 trimethylation (H3K27me3) on gene expression?
Activation of transcription
Repression of transcription
Increased mRNA stability
Enhanced translation efficiency
Explanation - H3K27me3 is a repressive mark that compacts chromatin and silences gene expression.
Correct answer is: Repression of transcription
Q.16 Which of the following best describes a cis‑regulatory element?
A protein that binds DNA
A DNA sequence located near the gene it regulates
A small RNA that degrades mRNA
A membrane receptor that signals transcription factors
Explanation - Cis‑regulatory elements (e.g., promoters, enhancers) are DNA regions that control transcription of nearby genes.
Correct answer is: A DNA sequence located near the gene it regulates
Q.17 During transcriptional activation, which co‑activator activity is most commonly recruited to promoters?
DNA methyltransferase
Histone deacetylase (HDAC)
Histone acetyltransferase (HAT)
RNA helicase
Explanation - HATs acetylate histones, creating an open chromatin structure that facilitates transcription.
Correct answer is: Histone acetyltransferase (HAT)
Q.18 Which of the following statements about operons is FALSE?
Operons are common in prokaryotes
Operons allow coordinated regulation of multiple genes
Each gene in an operon has its own promoter
Operons can be regulated by repressors and activators
Explanation - In an operon, multiple genes are transcribed from a single promoter into a polycistronic mRNA.
Correct answer is: Each gene in an operon has its own promoter
Q.19 What is the primary function of the RNA-induced silencing complex (RISC)?
To splice pre‑mRNA
To unwind DNA during replication
To guide microRNAs or siRNAs to target mRNAs for degradation
To add a 5′ cap to mRNA
Explanation - RISC uses guide RNAs to recognize complementary mRNA sequences and mediate their cleavage or translational repression.
Correct answer is: To guide microRNAs or siRNAs to target mRNAs for degradation
Q.20 Which of the following is NOT a typical characteristic of a eukaryotic enhancer?
Orientation‑independent activity
Works only when located upstream of the promoter
Can act over long distances
Can function in either direction relative to the gene
Explanation - Enhancers can function upstream, downstream, or within introns of the target gene and are orientation‑independent.
Correct answer is: Works only when located upstream of the promoter
Q.21 In the context of gene regulation, what does the term 'epigenetics' refer to?
Changes in DNA sequence that affect phenotype
Heritable changes in gene expression without DNA sequence alteration
Mutations in mitochondrial DNA
Alternative splicing patterns
Explanation - Epigenetics involves mechanisms like DNA methylation and histone modification that modulate gene activity without changing the nucleotide code.
Correct answer is: Heritable changes in gene expression without DNA sequence alteration
Q.22 Which of the following molecules serves as a second messenger that influences transcription of the lac operon?
cAMP
ATP
cGMP
IP3
Explanation - cAMP binds the catabolite activator protein (CAP), which then enhances lac operon transcription when glucose is low.
Correct answer is: cAMP
Q.23 What is the effect of a nonsense mutation within a coding region?
It changes one amino acid to another
It introduces a premature stop codon, truncating the protein
It removes an intron
It inserts a new exon
Explanation - A nonsense mutation converts a codon into a stop signal, leading to early termination of translation.
Correct answer is: It introduces a premature stop codon, truncating the protein
Q.24 Which of the following best explains why histone acetylation generally activates transcription?
Acetyl groups attract DNA polymerase
Acetylation neutralizes positive charges on histones, loosening DNA‑histone interaction
Acetyl groups act as transcription factors
Acetylation adds methyl groups to DNA
Explanation - Neutralizing lysine residues reduces histone affinity for negatively charged DNA, making the chromatin more accessible.
Correct answer is: Acetylation neutralizes positive charges on histones, loosening DNA‑histone interaction
Q.25 Which of the following is a characteristic of a constitutive promoter?
Active only under specific environmental conditions
Requires a specific activator protein
Continuously active, leading to constant gene expression
Inhibited by a repressor bound to an operator
Explanation - Constitutive promoters drive basal level transcription regardless of regulatory signals.
Correct answer is: Continuously active, leading to constant gene expression
Q.26 What is the main purpose of a silencer element in gene regulation?
To increase transcription rates
To recruit RNA polymerase
To repress transcription when bound by repressor proteins
To splice pre‑mRNA
Explanation - Silencers are DNA sequences that, upon binding repressor proteins, diminish transcriptional activity.
Correct answer is: To repress transcription when bound by repressor proteins
Q.27 Which of the following best describes the 'RNA polymerase II C‑terminal domain (CTD)' function?
Catalyzes DNA replication
Binds ribosomes for translation
Coordinates transcription with RNA processing events
Degrades misfolded proteins
Explanation - The CTD undergoes phosphorylation cycles that recruit capping, splicing, and polyadenylation factors during transcription.
Correct answer is: Coordinates transcription with RNA processing events
Q.28 In the context of gene regulation, what is 'feedback inhibition'?
A product of a pathway inhibits an enzyme earlier in that pathway
A gene product activates its own transcription
RNA polymerase degrades its own mRNA
Transcription factors are phosphorylated by kinases
Explanation - Feedback inhibition is a negative feedback loop where the end product reduces its own synthesis, often by inhibiting a key enzyme.
Correct answer is: A product of a pathway inhibits an enzyme earlier in that pathway
Q.29 Which of the following best illustrates the principle of 'inducible' gene expression?
A house‑keeping gene that is always expressed
The lac operon being turned on in the presence of lactose
A gene that is silenced by DNA methylation
A gene with a promoter lacking a TATA box
Explanation - Inducible systems are activated only when a specific signal (e.g., lactose) is present.
Correct answer is: The lac operon being turned on in the presence of lactose
Q.30 Which of the following statements about 'alternative splicing' is TRUE?
It occurs only in prokaryotes
It allows a single gene to produce multiple protein isoforms
It adds a 5′ cap to mRNA
It is mediated by DNA methyltransferases
Explanation - Alternative splicing rearranges exon inclusion, generating diverse proteins from one gene.
Correct answer is: It allows a single gene to produce multiple protein isoforms
Q.31 What is the effect of binding of the catabolite activator protein (CAP) to its site on the DNA?
It blocks RNA polymerase binding
It enhances RNA polymerase recruitment to the promoter
It degrades mRNA
It terminates transcription
Explanation - CAP-cAMP complex binds upstream of certain promoters (e.g., lac) and stimulates transcription initiation.
Correct answer is: It enhances RNA polymerase recruitment to the promoter
Q.32 Which histone modification is most strongly associated with transcriptional repression at promoters?
H3K4me3
H3K9me3
H3K27ac
H4K16ac
Explanation - Trimethylation of histone H3 at lysine 9 creates heterochromatin and silences gene expression.
Correct answer is: H3K9me3
Q.33 Which of the following is a characteristic of a 'repressible' operon?
It is turned on in the presence of a substrate
It is constitutively active
It is turned off when the end product accumulates
It requires a co‑activator for transcription
Explanation - Repressible operons are usually involved in biosynthetic pathways and are inhibited by the pathway end product.
Correct answer is: It is turned off when the end product accumulates
Q.34 What is the primary mechanism by which antisense oligonucleotides (ASOs) down‑regulate gene expression?
They bind DNA promoters and block transcription
They recruit ribosomes to increase translation
They hybridize to target mRNA, leading to RNase H‑mediated degradation
They add methyl groups to histones
Explanation - ASOs form DNA‑RNA hybrids that are recognized and cleaved by RNase H, reducing protein production.
Correct answer is: They hybridize to target mRNA, leading to RNase H‑mediated degradation
Q.35 Which of the following best explains why DNA looping facilitates enhancer‑promoter communication?
Looping changes the DNA sequence of the promoter
Looping brings distant DNA regions into close spatial proximity
Looping removes nucleosomes from the gene body
Looping degrades the enhancer
Explanation - Protein complexes can bend DNA, allowing enhancers located far away to interact with the transcriptional machinery at the promoter.
Correct answer is: Looping brings distant DNA regions into close spatial proximity
Q.36 Which of the following is NOT a typical outcome of RNA interference (RNAi)?
Degradation of target mRNA
Translational repression
DNA methylation of the gene promoter
Cleavage of double‑stranded RNA
Explanation - RNAi mainly acts at the post‑transcriptional level; it does not directly methylate DNA promoters.
Correct answer is: DNA methylation of the gene promoter
Q.37 In eukaryotic transcription, which factor is responsible for unwinding DNA at the transcription start site?
RNA polymerase I
TFIIH (helicase activity)
DNA ligase
Topoisomerase I
Explanation - TFIIH contains helicase subunits that unwind DNA downstream of the promoter, enabling RNA synthesis.
Correct answer is: TFIIH (helicase activity)
Q.38 Which of the following best describes a 'riboswitch'?
A DNA element that binds transcription factors
A protein that alters RNA polymerase activity
An RNA segment that changes conformation upon ligand binding to regulate gene expression
A membrane receptor that activates transcription
Explanation - Riboswitches are regulatory RNA domains that control transcription or translation in response to small molecules.
Correct answer is: An RNA segment that changes conformation upon ligand binding to regulate gene expression
Q.39 Which of the following statements about 'chromatin remodeling complexes' is correct?
They add methyl groups to DNA bases
They hydrolyze ATP to reposition nucleosomes
They synthesize ribosomal RNA
They splice introns from pre‑mRNA
Explanation - Chromatin remodelers use ATP energy to slide, evict, or restructure nucleosomes, affecting accessibility.
Correct answer is: They hydrolyze ATP to reposition nucleosomes
Q.40 Which of the following is an example of a post‑translational modification that can affect transcription factor activity?
Phosphorylation
Splicing
Transcription termination
DNA replication
Explanation - Adding phosphate groups can alter a transcription factor’s stability, localization, or DNA‑binding ability.
Correct answer is: Phosphorylation
Q.41 What is the main functional difference between a 'silencer' and an 'enhancer'?
Silencers are upstream, enhancers are downstream
Silencers repress transcription, enhancers activate transcription
Silencers bind RNA polymerase, enhancers bind ribosomes
Silencers are only found in prokaryotes
Explanation - Both are cis‑regulatory DNA elements, but silencers decrease and enhancers increase gene expression.
Correct answer is: Silencers repress transcription, enhancers activate transcription
Q.42 Which of the following is a common method used to identify DNA‑protein interactions genome‑wide?
Western blot
Chromatin immunoprecipitation followed by sequencing (ChIP‑seq)
PCR
Southern blot
Explanation - ChIP‑seq isolates DNA fragments bound by a specific protein and sequences them to map binding sites.
Correct answer is: Chromatin immunoprecipitation followed by sequencing (ChIP‑seq)
Q.43 Which of the following best describes the 'gene dosage effect'?
The number of gene copies influences the level of gene expression
A single mutation always leads to disease
Genes are only expressed in diploid cells
All genes are transcribed at equal rates
Explanation - Increasing or decreasing gene copy number can raise or lower the amount of product made from that gene.
Correct answer is: The number of gene copies influences the level of gene expression
Q.44 Which of the following is a characteristic of a 'latent' viral genome integrated into host DNA?
Constant high-level expression of viral proteins
No transcription of viral genes unless reactivated
Immediate lysis of the host cell
Production of viral capsids in the cytoplasm
Explanation - Latent viruses maintain their genome in host DNA with minimal transcription; reactivation triggers expression.
Correct answer is: No transcription of viral genes unless reactivated
Q.45 Which of the following best explains why 'histone variants' can affect gene expression?
They change the DNA sequence
They alter nucleosome stability and can recruit specific regulatory proteins
They directly bind RNA polymerase
They act as transcription factors
Explanation - Incorporation of variant histones changes chromatin dynamics, influencing accessibility and factor recruitment.
Correct answer is: They alter nucleosome stability and can recruit specific regulatory proteins
Q.46 What is the principal difference between a 'cis‑acting' and a 'trans‑acting' factor?
Cis‑acting factors are proteins; trans‑acting factors are RNAs
Cis‑acting factors act on the same DNA molecule; trans‑acting factors can act on different DNA molecules
Cis‑acting factors are found only in prokaryotes
Trans‑acting factors are always enzymes
Explanation - Cis elements are DNA sequences on the same molecule; trans factors are diffusible molecules (often proteins) that can affect any compatible DNA.
Correct answer is: Cis‑acting factors act on the same DNA molecule; trans‑acting factors can act on different DNA molecules
Q.47 Which of the following is an example of a 'feedback loop' that positively regulates gene expression?
A transcription factor that activates its own gene's expression
A metabolite that inhibits the first enzyme of its pathway
RNA polymerase degrading its own mRNA
A repressor that blocks its own synthesis
Explanation - Positive feedback amplifies expression when a product enhances its own production.
Correct answer is: A transcription factor that activates its own gene's expression
Q.48 Which of the following best describes the function of a 'polyadenylation signal' in eukaryotic mRNA?
It signals the start of translation
It directs the addition of a poly(A) tail to the 3′ end of the mRNA
It binds ribosomes for protein synthesis
It encodes a stop codon
Explanation - The AAUAAA sequence signals cleavage and polyadenylation, stabilizing mRNA and aiding export.
Correct answer is: It directs the addition of a poly(A) tail to the 3′ end of the mRNA
Q.49 What is the primary purpose of a 'reporter gene' in molecular biology experiments?
To produce a therapeutic protein
To provide a measurable output (e.g., fluorescence) indicating promoter activity
To silence endogenous genes
To act as a selectable marker for antibiotic resistance
Explanation - Reporter genes such as GFP or luciferase are fused to regulatory elements to monitor expression levels.
Correct answer is: To provide a measurable output (e.g., fluorescence) indicating promoter activity
Q.50 Which of the following best illustrates the concept of 'gene silencing' by heterochromatin formation?
DNA replication at the origin of replication
Condensation of chromatin around centromeres leading to transcriptional inactivity
Binding of RNA polymerase to a promoter
Splicing of introns from pre‑mRNA
Explanation - Heterochromatin is tightly packed DNA, often marked by H3K9me3, resulting in gene silencing.
Correct answer is: Condensation of chromatin around centromeres leading to transcriptional inactivity
Q.51 Which of the following best explains why the 'lac operon' is not expressed when glucose is abundant?
Glucose directly binds the lac repressor
High glucose lowers cAMP levels, reducing CAP activation of the promoter
Glucose degrades all mRNA in the cell
Glucose methylates the lac promoter
Explanation - Catabolite repression: glucose reduces intracellular cAMP, preventing CAP from enhancing lac transcription.
Correct answer is: High glucose lowers cAMP levels, reducing CAP activation of the promoter
Q.52 Which of the following is true about 'RNA polymerase III' transcription products?
They include mRNA encoding proteins
They transcribe tRNA and 5S rRNA genes
They synthesize large ribosomal RNAs (18S, 28S)
They are only active in prokaryotes
Explanation - RNA Pol III is responsible for synthesizing small structural RNAs like tRNAs and 5S rRNA.
Correct answer is: They transcribe tRNA and 5S rRNA genes
Q.53 Which of the following best describes a 'homeotic gene'?
A gene that controls the body plan by specifying segment identity
A gene that encodes ribosomal proteins
A gene involved in DNA replication
A gene that degrades mRNA
Explanation - Homeotic genes (e.g., Hox genes) determine positional identity during development.
Correct answer is: A gene that controls the body plan by specifying segment identity
Q.54 What is the main functional difference between 'cis‑acting' enhancers and 'trans‑acting' transcription factors?
Enhancers are proteins; transcription factors are DNA sequences
Enhancers are DNA elements that act locally; transcription factors are diffusible proteins that can act on distant genes
Both are located on the same chromosome as their target gene
Both are RNA molecules
Explanation - Cis‑acting enhancers are DNA sequences that influence nearby genes, while trans‑acting factors are proteins that can travel throughout the nucleus.
Correct answer is: Enhancers are DNA elements that act locally; transcription factors are diffusible proteins that can act on distant genes
Q.55 Which of the following best explains why the presence of a 'TATA box' is not essential for all promoters?
All promoters contain a TATA box but it is sometimes hidden
Some promoters use other core elements (e.g., Initiator (Inr) or DPE) to recruit transcription machinery
TATA boxes are only found in prokaryotes
TATA boxes are replaced by ribosomes in eukaryotes
Explanation - Promoters can have alternative core motifs that facilitate transcription initiation without a TATA box.
Correct answer is: Some promoters use other core elements (e.g., Initiator (Inr) or DPE) to recruit transcription machinery
Q.56 Which of the following mechanisms can lead to gene silencing without changes in DNA sequence?
Point mutations
DNA methylation and histone modification
Insertion of a transposon
Deletion of an exon
Explanation - Epigenetic modifications alter chromatin state and gene expression without altering the nucleotide sequence.
Correct answer is: DNA methylation and histone modification
Q.57 What is the principal role of the 'poly(A) binding protein (PABP)' in eukaryotic cells?
To initiate transcription
To facilitate nuclear export and translation of mRNA by binding the poly(A) tail
To splice introns
To degrade mRNA
Explanation - PABP binds the poly(A) tail, protecting mRNA and interacting with translation factors.
Correct answer is: To facilitate nuclear export and translation of mRNA by binding the poly(A) tail
Q.58 Which of the following best describes the function of a 'riboswitch' located in the 5′ untranslated region (UTR) of an mRNA?
It codes for a protein that degrades DNA
It directly binds a metabolite, altering the mRNA secondary structure to control translation initiation
It recruits RNA polymerase to start transcription
It serves as a site for DNA replication
Explanation - Riboswitches sense small molecules and modulate gene expression by changing mRNA conformation.
Correct answer is: It directly binds a metabolite, altering the mRNA secondary structure to control translation initiation
Q.59 Which of the following is an example of a post‑transcriptional regulatory mechanism?
DNA methylation of a promoter
Alternative splicing of pre‑mRNA
Binding of a repressor to an operator
Acetylation of histones
Explanation - Post‑transcriptional regulation occurs after transcription, influencing mRNA processing, stability, or translation.
Correct answer is: Alternative splicing of pre‑mRNA
Q.60 Which of the following best explains why 'RNA polymerase I' transcribes rRNA genes in the nucleolus?
It can bind to the TATA box
It has a high affinity for promoters of ribosomal DNA located in the nucleolus
It is the only polymerase that can bind DNA
It also synthesizes tRNA
Explanation - RNA Pol I specifically recognizes rDNA promoters and transcribes the large rRNA precursor in the nucleolus.
Correct answer is: It has a high affinity for promoters of ribosomal DNA located in the nucleolus
Q.61 In the context of gene regulation, what does the term 'dose‑dependent response' refer to?
A gene's expression level changes proportionally to the concentration of a regulatory molecule
A gene is either fully on or fully off with no intermediate states
All genes respond equally to any stimulus
The number of ribosomes determines transcription rate
Explanation - Dose‑dependent responses show graded changes in expression as the amount of inducer or repressor varies.
Correct answer is: A gene's expression level changes proportionally to the concentration of a regulatory molecule
Q.62 Which of the following is true about 'operon' regulation in eukaryotes?
Eukaryotes commonly use operons to co‑regulate genes
Eukaryotic genes are typically transcribed individually with separate promoters
Operons are the main mechanism of transcription in humans
Eukaryotic operons are regulated only by repressors
Explanation - Operons are a prokaryotic feature; eukaryotes generally have monocistronic transcription units.
Correct answer is: Eukaryotic genes are typically transcribed individually with separate promoters
Q.63 Which of the following best describes the function of a 'co‑activator' in transcription?
It directly binds DNA to initiate transcription
It modifies chromatin or recruits the transcriptional machinery without binding DNA directly
It degrades mRNA after translation
It serves as a ribosomal subunit
Explanation - Co‑activators interact with transcription factors and remodel chromatin, enhancing transcription.
Correct answer is: It modifies chromatin or recruits the transcriptional machinery without binding DNA directly
Q.64 Which of the following is a hallmark of 'RNA polymerase II pausing' during transcription?
RNA polymerase terminates immediately after initiation
RNA polymerase synthesizes a short transcript and pauses near the promoter before productive elongation
RNA polymerase does not require a promoter
RNA polymerase only transcribes introns
Explanation - Promoter-proximal pausing is a regulatory step allowing rapid response to signals.
Correct answer is: RNA polymerase synthesizes a short transcript and pauses near the promoter before productive elongation
Q.65 Which of the following best explains why 'CpG islands' are often found near gene promoters?
They attract RNA polymerase directly
They are regions of high CpG dinucleotide frequency that remain unmethylated, allowing transcription
They encode transcription factors
They are binding sites for ribosomes
Explanation - Unmethylated CpG islands keep promoters accessible, facilitating gene activation.
Correct answer is: They are regions of high CpG dinucleotide frequency that remain unmethylated, allowing transcription
Q.66 Which of the following is an example of a 'negative feedback loop' in gene regulation?
A transcription factor that activates its own expression
An enzyme that, when produced in excess, represses its own gene's transcription
A metabolite that induces the expression of the enzymes that produce it
A ribosome that increases the rate of its own synthesis
Explanation - Negative feedback reduces expression when product levels become high, maintaining homeostasis.
Correct answer is: An enzyme that, when produced in excess, represses its own gene's transcription
Q.67 Which of the following best characterizes a 'synthetic biology' approach to gene regulation?
Using natural promoters only
Engineering artificial regulatory circuits (e.g., toggle switches) to control gene expression in a predictable manner
Studying gene regulation in extinct species
Sequencing genomes without functional analysis
Explanation - Synthetic biology designs custom genetic parts to build novel regulatory networks.
Correct answer is: Engineering artificial regulatory circuits (e.g., toggle switches) to control gene expression in a predictable manner
Q.68 Which of the following best explains how a 'DNA‑binding domain' (DBD) contributes to transcription factor specificity?
It phosphorylates the transcription factor
It recognizes and binds specific DNA sequences, directing the factor to its target genes
It degrades RNA polymerase
It adds methyl groups to histones
Explanation - The DBD determines which promoter or enhancer regions a transcription factor can bind.
Correct answer is: It recognizes and binds specific DNA sequences, directing the factor to its target genes
Q.69 Which of the following is a typical characteristic of genes regulated by a 'feed‑forward loop'?
The regulator activates the target gene and also activates a second regulator that further enhances the target
The regulator only represses the target gene
The target gene directly inhibits its own promoter
The loop involves only post‑translational modifications
Explanation - In a coherent feed‑forward loop, the initial regulator and a secondary regulator both activate the target, creating a rapid yet filtered response.
Correct answer is: The regulator activates the target gene and also activates a second regulator that further enhances the target
Q.70 Which of the following best describes the function of a 'promoter proximal element' (PPE)?
A DNA sequence that directly initiates transcription termination
A region immediately downstream of the transcription start site that can bind transcription factors influencing initiation
A protein that degrades mRNA
A ribosomal binding site in prokaryotes
Explanation - PPEs are located near promoters and modulate transcription efficiency through factor binding.
Correct answer is: A region immediately downstream of the transcription start site that can bind transcription factors influencing initiation
Q.71 Which of the following best explains why 'RNA polymerase II' requires a C‑terminal domain (CTD) with multiple repeats?
The repeats serve as binding sites for factors involved in capping, splicing, and polyadenylation
They code for the polymerase's catalytic activity
They are necessary for DNA replication
They bind ribosomes during translation
Explanation - CTD phosphorylation creates a platform for co‑transcriptional processing factors.
Correct answer is: The repeats serve as binding sites for factors involved in capping, splicing, and polyadenylation
Q.72 Which of the following best describes a 'chromatin insulator'?
A DNA element that blocks the spread of heterochromatin and prevents enhancers from activating unintended genes
A protein that degrades mRNA
A ribosomal RNA component
An enzyme that methylates DNA
Explanation - Insulators demarcate boundaries between active and inactive chromatin domains.
Correct answer is: A DNA element that blocks the spread of heterochromatin and prevents enhancers from activating unintended genes
Q.73 Which of the following mechanisms can lead to the rapid down‑regulation of a protein without altering transcription?
DNA methylation
Ubiquitination followed by proteasomal degradation
Histone acetylation
RNA splicing
Explanation - Post‑translational tagging with ubiquitin targets proteins for rapid degradation by the proteasome.
Correct answer is: Ubiquitination followed by proteasomal degradation
Q.74 Which of the following best illustrates the principle of 'synthetic lethality' in gene regulation research?
Knocking out either of two genes individually has no effect, but simultaneous loss is lethal
Overexpressing a gene always leads to cell death
Mutating a promoter increases transcription rate
Silencing a gene always rescues a disease phenotype
Explanation - Synthetic lethality exploits redundant pathways; targeting both can selectively kill cells (e.g., cancer cells).
Correct answer is: Knocking out either of two genes individually has no effect, but simultaneous loss is lethal
Q.75 Which of the following best describes the role of 'long non‑coding RNAs' (lncRNAs) in gene regulation?
They encode transcription factors
They act as scaffolds to recruit chromatin modifiers to specific genomic loci
They are translated into enzymes
They serve as tRNAs for protein synthesis
Explanation - lncRNAs can guide epigenetic regulators to target genes, influencing chromatin state and transcription.
Correct answer is: They act as scaffolds to recruit chromatin modifiers to specific genomic loci
Q.76 Which of the following best explains why the 'CRISPRi' (CRISPR interference) system can repress transcription without cutting DNA?
Catalytically dead Cas9 (dCas9) blocks RNA polymerase binding or elongation when guided to a promoter
dCas9 adds methyl groups to DNA
CRISPRi degrades the mRNA directly
dCas9 recruits ribosomes to the gene
Explanation - dCas9 lacks nuclease activity but can sterically hinder transcription machinery when targeted to regulatory regions.
Correct answer is: Catalytically dead Cas9 (dCas9) blocks RNA polymerase binding or elongation when guided to a promoter
Q.77 Which of the following is a defining feature of 'bacterial operon attenuation'?
Regulation through premature transcription termination mediated by RNA secondary structures
Methylation of promoter DNA
Splicing of introns
Binding of a repressor to an operator
Explanation - Attenuation uses leader peptide translation to form terminator or anti‑terminator hairpins, controlling transcription of downstream genes.
Correct answer is: Regulation through premature transcription termination mediated by RNA secondary structures
Q.78 Which of the following best describes the principle behind 'reporter assays' using luciferase?
Luciferase directly binds DNA to activate transcription
Luminescence emitted by luciferase activity provides a quantitative read‑out of promoter or enhancer activity
Luciferase degrades mRNA
Luciferase functions as a ribosomal subunit
Explanation - Luciferase converts luciferin to light; intensity correlates with the activity of the regulatory element driving its expression.
Correct answer is: Luminescence emitted by luciferase activity provides a quantitative read‑out of promoter or enhancer activity
Q.79 Which of the following best explains why 'DNA‑binding proteins' often contain 'helix‑turn‑helix' motifs?
This motif allows the protein to insert into the major groove of DNA and recognize specific base pairs
It catalyzes RNA synthesis
It transports proteins across the nuclear membrane
It degrades DNA
Explanation - The helix‑turn‑helix structure fits into DNA's major groove, enabling sequence‑specific interactions.
Correct answer is: This motif allows the protein to insert into the major groove of DNA and recognize specific base pairs
Q.80 Which of the following best describes the effect of a 'strong enhancer' placed downstream of a gene's coding region?
It will silence the gene
It can increase transcription levels despite being downstream, due to DNA looping
It will cause the gene to be spliced out
It will change the reading frame of the gene
Explanation - Enhancers function irrespective of orientation or distance; they act through looping to contact promoters.
Correct answer is: It can increase transcription levels despite being downstream, due to DNA looping
Q.81 Which of the following best explains why 'CpG methylation' in promoter regions is generally associated with gene silencing?
Methyl groups directly block the polymerase active site
Methylated CpGs recruit proteins that compact chromatin and prevent transcription factor binding
Methylation converts DNA to RNA
Methyl groups increase transcription factor affinity
Explanation - Methyl-CpG binding proteins attract histone deacetylases and other repressors, leading to a closed chromatin state.
Correct answer is: Methylated CpGs recruit proteins that compact chromatin and prevent transcription factor binding
Q.82 Which of the following best characterizes 'RNA polymerase pausing' as a regulatory mechanism?
RNA polymerase terminates transcription immediately after initiation
RNA polymerase halts shortly after initiation, allowing signals to determine whether elongation proceeds
RNA polymerase degrades the DNA template
RNA polymerase only transcribes non‑coding regions
Explanation - Promoter-proximal pausing provides a checkpoint for rapid gene activation upon receiving appropriate cues.
Correct answer is: RNA polymerase halts shortly after initiation, allowing signals to determine whether elongation proceeds
Q.83 Which of the following is a primary advantage of using a 'Tet‑On' system in inducible gene expression experiments?
Gene expression is turned off in the presence of tetracycline
Gene expression is turned on only when tetracycline (or doxycycline) is added, allowing temporal control
It permanently integrates into the genome without regulation
It does not require any transcription factors
Explanation - The Tet‑On system uses a tetracycline‑responsive transcriptional activator that activates transcription upon drug addition.
Correct answer is: Gene expression is turned on only when tetracycline (or doxycycline) is added, allowing temporal control
Q.84 Which of the following best describes the concept of 'chromatin accessibility' measured by ATAC‑seq?
Sequencing of DNA methylation patterns
Identification of open chromatin regions where transposase can insert adapters, indicating active regulatory elements
Quantification of RNA levels
Mapping of protein‑protein interactions
Explanation - ATAC‑seq uses a hyperactive Tn5 transposase to tag accessible DNA, revealing active promoters, enhancers, and other regulatory sites.
Correct answer is: Identification of open chromatin regions where transposase can insert adapters, indicating active regulatory elements
Q.85 Which of the following best explains why 'histone H3 lysine 4 trimethylation (H3K4me3)' is associated with active promoters?
It recruits DNA polymerase for replication
It creates a binding platform for transcription initiation complexes
It directly binds to RNA polymerase II catalytic core
It signals for DNA degradation
Explanation - H3K4me3 marks active promoters and recruits factors like TAFs and chromatin remodelers that facilitate transcription.
Correct answer is: It creates a binding platform for transcription initiation complexes
Q.86 Which of the following best describes the function of a 'ribosome profiling' experiment?
To measure DNA replication timing
To capture and sequence ribosome‑protected mRNA fragments, providing a snapshot of translation
To identify transcription factor binding sites
To detect DNA methylation
Explanation - Ribosome profiling (Ribo‑seq) isolates mRNA fragments protected by ribosomes, revealing which transcripts are being actively translated.
Correct answer is: To capture and sequence ribosome‑protected mRNA fragments, providing a snapshot of translation
Q.87 Which of the following best illustrates the principle of 'synthetic gene circuits' used in biotechnology?
A natural operon controlling lactose metabolism
Engineered constructs that combine promoters, repressors, and feedback loops to produce desired expression dynamics (e.g., oscillators)
Random integration of genes into the genome
Sequencing of the human genome
Explanation - Synthetic circuits are designed to perform specific functions, such as toggle switches or oscillators, by arranging regulatory parts in defined architectures.
Correct answer is: Engineered constructs that combine promoters, repressors, and feedback loops to produce desired expression dynamics (e.g., oscillators)
Q.88 Which of the following best explains why 'DNA‑binding proteins' often contain multiple domains (e.g., DBD, activation domain)?
To allow simultaneous DNA binding and recruitment of transcriptional machinery
To degrade DNA
To act as ribosomal subunits
To splice RNA
Explanation - Modular architecture enables a protein to recognize specific DNA sequences (DBD) and interact with co‑activators or repressors (activation/repression domains).
Correct answer is: To allow simultaneous DNA binding and recruitment of transcriptional machinery
Q.89 Which of the following best describes a 'dose‑responsive element' (DRE) in gene regulation?
A DNA sequence that responds to varying concentrations of a specific ligand or signal to modulate transcription levels
A protein that degrades mRNA
An RNA molecule that codes for a transcription factor
A region that initiates DNA replication
Explanation - DREs allow graded transcriptional responses depending on the amount of the activating or repressing molecule present.
Correct answer is: A DNA sequence that responds to varying concentrations of a specific ligand or signal to modulate transcription levels