Q.1 Which process involves a bacterial cell taking up free DNA from its environment?
Conjugation
Transduction
Transformation
Transcription
Explanation - Transformation is the natural uptake of naked DNA from the surrounding medium by a bacterial cell.
Correct answer is: Transformation
Q.2 What is the primary function of plasmids in bacterial genetics?
Provide a template for RNA synthesis
Store essential chromosomal genes
Carry accessory genes that can be transferred between cells
Regulate the cell cycle
Explanation - Plasmids are extrachromosomal DNA elements that often encode accessory genes, such as antibiotic resistance, and can be transferred between bacteria.
Correct answer is: Carry accessory genes that can be transferred between cells
Q.3 Which viral protein is responsible for packaging bacterial DNA into a phage head during transduction?
DNA polymerase
Capsid protein
Helix-turn-helix protein
Transposase
Explanation - The capsid protein forms the viral head and is responsible for packaging DNA during transduction.
Correct answer is: Capsid protein
Q.4 Which of the following best describes the mechanism of bacterial conjugation?
Direct uptake of free DNA from the environment
Transfer of DNA via a phage particle
Transfer of DNA through a sex pilus between two cells
Random insertion of DNA into the genome
Explanation - Conjugation involves a donor cell forming a sex pilus to transfer a plasmid or chromosomal fragment to a recipient cell.
Correct answer is: Transfer of DNA through a sex pilus between two cells
Q.5 CRISPR-Cas systems are best known for providing:
High-speed DNA replication
Adaptive immunity against phages
Efficient protein synthesis
Enhanced metabolic pathways
Explanation - CRISPR-Cas systems serve as an adaptive immune mechanism in bacteria and archaea, storing short sequences from invaders and targeting them for degradation.
Correct answer is: Adaptive immunity against phages
Q.6 In bacterial genetics, a mutation that changes a codon to encode a different amino acid is called a:
Nonsense mutation
Missense mutation
Silent mutation
Frameshift mutation
Explanation - A missense mutation changes a codon to code for a different amino acid, potentially altering protein function.
Correct answer is: Missense mutation
Q.7 Which type of recombination event is most likely to increase genetic diversity during bacterial conjugation?
Homologous recombination
Non-homologous end joining
Transcriptional coupling
DNA replication slippage
Explanation - Homologous recombination during conjugation integrates transferred DNA into the recipient genome, creating new genetic combinations.
Correct answer is: Homologous recombination
Q.8 A transposon that can excise itself from one DNA location and integrate into another is known as a:
Retrotransposon
DNA transposon
Transposase gene
Insertion sequence
Explanation - DNA transposons encode transposase that allows the element to cut and paste within the genome.
Correct answer is: DNA transposon
Q.9 Which of the following best describes the term 'lysogenic cycle' in phage biology?
The phage immediately lyses the host cell after infection
The phage integrates its DNA into the host genome and replicates with it
The phage uses host machinery to produce new phages without integration
The phage is completely inactivated within the host
Explanation - In the lysogenic cycle, the phage genome becomes a prophage integrated into the bacterial chromosome.
Correct answer is: The phage integrates its DNA into the host genome and replicates with it
Q.10 What is the role of the SOS response in bacterial genetics?
To promote cell division during stress
To repair DNA damage and induce mutagenesis
To shut down all transcriptional activity
To facilitate plasmid replication
Explanation - The SOS response is a global regulatory network that activates DNA repair enzymes and error-prone polymerases during damage.
Correct answer is: To repair DNA damage and induce mutagenesis
Q.11 Which enzyme is primarily responsible for the excision of integrated phage DNA during induction of the lytic cycle?
Integrase
Excisionase
RNA polymerase
Helicase
Explanation - Excisionase, along with integrase, mediates the removal of prophage DNA during transition to the lytic cycle.
Correct answer is: Excisionase
Q.12 In bacterial conjugation, the DNA that is transferred typically contains:
Only ribosomal RNA genes
A full copy of the bacterial chromosome
Plasmid DNA, sometimes with chromosomal segments
Only protein coding genes for metabolism
Explanation - Conjugation primarily transfers plasmids, but can also move chromosomal DNA segments via the tra region.
Correct answer is: Plasmid DNA, sometimes with chromosomal segments
Q.13 Which molecular tool allows researchers to selectively edit bacterial genomes with high precision?
CRISPR-Cas9
PCR amplification
Gel electrophoresis
Mass spectrometry
Explanation - CRISPR-Cas9 uses guide RNAs to target specific DNA sequences for precise cutting and editing.
Correct answer is: CRISPR-Cas9
Q.14 The term 'genomic island' refers to:
A region of the genome that is highly conserved across species
A mobile genetic element that can be transferred horizontally
A structural component of bacterial ribosomes
An area where DNA replication begins
Explanation - Genomic islands are large DNA segments acquired through horizontal gene transfer, often carrying virulence or resistance genes.
Correct answer is: A mobile genetic element that can be transferred horizontally
Q.15 Which bacterial enzyme is involved in site-specific recombination for plasmid replication initiation?
Gyrase
Topoisomerase IV
Relaxase
DNA ligase
Explanation - Relaxase initiates plasmid transfer by nicking at the origin of transfer (oriT) during conjugation.
Correct answer is: Relaxase
Q.16 During which phase of bacterial cell cycle does the cell prepare to divide?
G1
S
G2
M
Explanation - The G2 phase involves growth and preparation for mitosis, similar to eukaryotic cell cycles.
Correct answer is: G2
Q.17 Which of the following is a classic example of a bacterial gene that is regulated by a repressor?
lacZ
rpoD
ftsZ
gyrA
Explanation - The lac operon is a well-known system where the lacI repressor regulates lacZ expression in the absence of lactose.
Correct answer is: lacZ
Q.18 What does the acronym 'PCR' stand for in molecular genetics?
Protein Conjugation Reaction
Polymerase Chain Reaction
Phage-Cell Recombination
Plasmid Circular Replication
Explanation - PCR is a technique to amplify a specific DNA segment exponentially using DNA polymerase.
Correct answer is: Polymerase Chain Reaction
Q.19 Which factor determines the rate of mutation in bacterial populations?
Temperature alone
DNA polymerase fidelity and DNA repair mechanisms
The size of the bacterial cell
Presence of plasmids only
Explanation - Mutation rates are influenced by how accurately polymerases synthesize DNA and how effectively repair systems correct errors.
Correct answer is: DNA polymerase fidelity and DNA repair mechanisms
Q.20 Which of the following is NOT a type of horizontal gene transfer?
Transformation
Conjugation
Transduction
Replication
Explanation - Replication is the process of duplicating the genome, not a transfer between cells.
Correct answer is: Replication
Q.21 The 'oriC' sequence in bacterial DNA is essential for:
Transcription initiation
DNA replication initiation
Protein translation initiation
Transposon insertion
Explanation - oriC is the origin of chromosomal replication where helicase loading begins.
Correct answer is: DNA replication initiation
Q.22 Which component of the bacterial cell membrane is involved in energy production during aerobic respiration?
Peptidoglycan layer
Lipid bilayer
Cytochrome c oxidase complex
Nucleoid region
Explanation - The cytochrome complex in the membrane generates the proton gradient used for ATP synthesis.
Correct answer is: Cytochrome c oxidase complex
Q.23 What is the main function of the lacI gene product in the lac operon?
Activate RNA polymerase
Inhibit transcription by binding to the operator
Synthesize lactose
Repair DNA damage
Explanation - LacI encodes a repressor that binds the operator to block transcription of lac genes when lactose is absent.
Correct answer is: Inhibit transcription by binding to the operator
Q.24 Which of the following describes a 'kill switch' in engineered bacteria?
A mechanism that promotes rapid growth
A genetic circuit that induces cell death under specific conditions
A plasmid that carries antibiotic resistance
An enzyme that repairs DNA
Explanation - Kill switches are safety features that cause engineered cells to die if they escape controlled environments.
Correct answer is: A genetic circuit that induces cell death under specific conditions
Q.25 The process by which a bacterial cell incorporates foreign DNA from a plasmid is called:
Conjugation
Transformation
Transduction
Transcription
Explanation - Transformation is the uptake of plasmid DNA from the environment by a bacterial cell.
Correct answer is: Transformation
Q.26 In the context of bacterial genetics, what does the term 'antibiotic resistance gene' refer to?
A gene that encodes ribosomal RNA
A gene that provides a selective advantage in the presence of antibiotics
A gene involved in DNA replication
A gene that codes for metabolic enzymes
Explanation - Antibiotic resistance genes encode proteins that neutralize antibiotics or prevent their uptake.
Correct answer is: A gene that provides a selective advantage in the presence of antibiotics
Q.27 Which bacterial system can act as a type II restriction-modification system?
CRISPR-Cas
Restriction enzyme R, methyltransferase M
Transposase
RNA polymerase
Explanation - Type II restriction-modification systems consist of a restriction enzyme that cuts DNA and a methylase that protects host DNA.
Correct answer is: Restriction enzyme R, methyltransferase M
Q.28 The term 'fitness cost' in bacterial genetics refers to:
The energy required to grow a cell
The disadvantage of carrying a plasmid or mutation in the absence of selective pressure
The rate of DNA replication
The amount of protein produced
Explanation - Fitness cost is the negative impact on growth or reproduction when a bacterium carries extra genetic material.
Correct answer is: The disadvantage of carrying a plasmid or mutation in the absence of selective pressure
Q.29 Which bacterial gene cluster is responsible for the synthesis of a complex polysaccharide capsule?
capsule operon
ribosomal operon
DNA repair operon
cell division operon
Explanation - The capsule operon encodes enzymes that assemble and export the capsular polysaccharide.
Correct answer is: capsule operon
Q.30 In bacterial genetics, what does 'allelic exchange' involve?
Replacing a gene with a variant allele via homologous recombination
Switching DNA strands during replication
Transferring plasmids between cells
Converting RNA to DNA
Explanation - Allelic exchange uses homologous recombination to replace a native allele with a mutated version.
Correct answer is: Replacing a gene with a variant allele via homologous recombination
Q.31 Which enzyme is essential for DNA replication initiation at the bacterial origin of replication?
DNA gyrase
DNA polymerase I
DnaA
Ligase
Explanation - DnaA is a replication initiation protein that binds to the oriC region to start DNA replication.
Correct answer is: DnaA
Q.32 What is a 'phage integrase' used for in bacterial genetics?
To integrate a phage genome into bacterial DNA
To excise plasmids from the chromosome
To degrade mRNA
To synthesize proteins
Explanation - Phage integrase catalyzes the site-specific recombination that inserts the phage genome into the host chromosome.
Correct answer is: To integrate a phage genome into bacterial DNA
Q.33 Which of the following is NOT a form of DNA repair in bacteria?
Mismatch repair
Base excision repair
Translesion synthesis
Protein synthesis
Explanation - Protein synthesis is not a DNA repair mechanism; it produces proteins from mRNA.
Correct answer is: Protein synthesis
Q.34 Which bacterial process is most relevant to the development of antibiotic resistance?
Transformation
Transduction
Conjugation
All of the above
Explanation - All three horizontal gene transfer mechanisms can spread resistance genes among bacterial populations.
Correct answer is: All of the above
Q.35 The 'OriT' sequence in a plasmid is recognized by which protein during conjugation?
DnaA
Relaxase
Ligase
RNA polymerase
Explanation - Relaxase nicks at OriT to initiate transfer of plasmid DNA during conjugation.
Correct answer is: Relaxase
Q.36 Which of the following best describes a 'knockout mutant' in bacterial genetics?
A strain with an additional copy of a gene
A strain where a specific gene has been deleted or inactivated
A strain that overexpresses a gene
A strain that has no genetic modifications
Explanation - Knockouts are created by removing or disrupting a gene to study its function.
Correct answer is: A strain where a specific gene has been deleted or inactivated
Q.37 In a plasmid-based reporter system, the GFP gene is used to monitor:
DNA replication
Gene expression
Protein folding
RNA splicing
Explanation - GFP fluorescence indicates the activity of promoters or regulatory elements driving its expression.
Correct answer is: Gene expression
Q.38 Which of the following is a key advantage of bacterial conjugation over transformation?
Higher frequency of DNA uptake
Can transfer large DNA fragments
Requires no physical contact
Occurs only in the presence of phages
Explanation - Conjugation can mobilize large plasmids and chromosomal segments, whereas transformation typically handles smaller DNA pieces.
Correct answer is: Can transfer large DNA fragments
Q.39 What is the primary purpose of the 'oriV' in bacterial plasmids?
Initiate viral replication
Serve as the origin of plasmid replication
Mark the site for DNA methylation
Control transcription of virulence genes
Explanation - oriV is the origin of replication for many plasmids, allowing them to replicate independently of the chromosome.
Correct answer is: Serve as the origin of plasmid replication
Q.40 The 'lambda' phage lifecycle includes a decision point between which two outcomes?
Lytic or lysogenic
Transcription or translation
Replication or recombination
Conjugation or transformation
Explanation - Lambda phage can choose to destroy the host (lytic) or integrate into the genome (lysogenic).
Correct answer is: Lytic or lysogenic
Q.41 Which bacterial enzyme is involved in the repair of UV-induced thymine dimers?
DNA polymerase II
Photolyase
Ligase
RNA polymerase
Explanation - Photolyase uses light energy to cleave thymine dimers, repairing UV-induced damage.
Correct answer is: Photolyase
Q.42 The 'lacZ' gene encodes which enzyme?
Beta-galactosidase
Alpha-amylase
Protease
Ligase
Explanation - lacZ codes for beta-galactosidase, which hydrolyzes lactose into glucose and galactose.
Correct answer is: Beta-galactosidase
Q.43 Which of these is an example of a mobile genetic element that can excise itself via a replicative transposition mechanism?
Transposon IS1
Prophage lambda
Plasmid pUC19
rRNA operon
Explanation - IS1 uses a copy-out-paste mechanism to transpose, creating a copy in the new location.
Correct answer is: Transposon IS1
Q.44 During bacterial transformation, the DNA is taken up into which part of the cell first?
Nucleus
Cytoplasm
Periplasmic space
Membrane vesicles
Explanation - The naked DNA diffuses into the cytoplasm where it can integrate into the genome or form a plasmid.
Correct answer is: Cytoplasm
Q.45 Which type of mutation results in a stop codon being introduced prematurely in a coding sequence?
Missense mutation
Nonsense mutation
Silent mutation
Frameshift mutation
Explanation - A nonsense mutation converts a sense codon into a stop codon, truncating the protein.
Correct answer is: Nonsense mutation
Q.46 Which bacterial DNA repair pathway specifically corrects mismatched base pairs after DNA replication?
Nucleotide excision repair
Base excision repair
Mismatch repair
Homologous recombination repair
Explanation - Mismatch repair identifies and corrects base-pair mismatches that escape proofreading during replication.
Correct answer is: Mismatch repair
Q.47 The term 'antigenic variation' refers to:
Changes in the surface proteins of a pathogen to evade the immune system
Alteration of metabolic pathways
The switching of plasmid origins of replication
Random DNA replication errors
Explanation - Antigenic variation involves changing surface antigens so the host immune system cannot recognize them.
Correct answer is: Changes in the surface proteins of a pathogen to evade the immune system
Q.48 In bacterial genetics, a 'gene knockout' can be achieved by:
Overexpressing the gene
Deleting the gene via homologous recombination
Adding extra copies of the gene
Silencing the gene with siRNA
Explanation - Gene knockouts remove or disrupt the target gene to study its function.
Correct answer is: Deleting the gene via homologous recombination
Q.49 What is the primary difference between type I and type II restriction enzymes?
Type I cuts at the target site, type II cuts nearby
Type I requires ATP, type II does not
Type I recognizes palindromic sequences, type II does not
Type I is bacterial, type II is viral
Explanation - Type I restriction enzymes are ATP-dependent and cut far from their recognition sites, while type II cut within their specific recognition sequences.
Correct answer is: Type I requires ATP, type II does not
Q.50 Which bacterial process is used to create a library of random DNA fragments for cloning?
Restriction digest
PCR amplification
Transduction
Transformation
Explanation - Restriction enzymes cut DNA at random sites to generate a library of fragments for cloning.
Correct answer is: Restriction digest
Q.51 In bacterial conjugation, the 'sex pilus' is primarily made of which protein?
F pilin
DNA polymerase
RNA polymerase
Transposase
Explanation - F pilin is the subunit protein that forms the conjugation pilus for DNA transfer.
Correct answer is: F pilin
Q.52 A 'promoter' in bacteria is:
A DNA region where RNA polymerase binds to initiate transcription
A protein that synthesizes DNA
A ribosome component
A DNA repair enzyme
Explanation - Promoters provide a binding site for RNA polymerase to start transcription of downstream genes.
Correct answer is: A DNA region where RNA polymerase binds to initiate transcription
Q.53 The 'oriC' region of bacterial DNA is recognized by which protein to begin replication?
DnaA
Pol I
Ligase
RNA polymerase
Explanation - DnaA binds oriC to initiate chromosomal replication.
Correct answer is: DnaA
Q.54 Which of the following is a common method to induce the lytic cycle in lysogenic bacteria?
Addition of IPTG
Exposure to UV light
Low temperature
High salt concentration
Explanation - UV light causes DNA damage that triggers induction of the lytic cycle in lysogenic phages.
Correct answer is: Exposure to UV light
Q.55 Which bacterial enzyme is responsible for creating a 5' end nick during plasmid transfer?
Relaxase
Pol III
Ligase
Transposase
Explanation - Relaxase nicks at the origin of transfer (OriT) to initiate plasmid mobilization.
Correct answer is: Relaxase
Q.56 Which of the following best describes the function of the 'lexA' gene in bacteria?
Encodes a repressor that terminates the SOS response
Encodes a DNA polymerase
Encodes a ribosomal protein
Encodes a structural protein of the cell wall
Explanation - LexA is a repressor that shuts down SOS genes when DNA damage is repaired.
Correct answer is: Encodes a repressor that terminates the SOS response
Q.57 What is the primary role of the 'lacY' gene in E. coli?
To synthesize beta-galactosidase
To transport lactose across the cell membrane
To regulate transcription
To repair DNA
Explanation - lacY encodes a permease that transports lactose into the cell.
Correct answer is: To transport lactose across the cell membrane
Q.58 Which of the following is a characteristic of a 'pseudogene' in bacterial genomes?
An inactive gene that has lost its function
A gene that codes for ribosomal RNA
A gene that is highly expressed
A plasmid-encoded gene
Explanation - Pseudogenes are remnants of once-functional genes that have become inactive due to mutations.
Correct answer is: An inactive gene that has lost its function
Q.59 Which enzyme is required for the replication of bacterial plasmids with a low copy number?
DnaB helicase
DnaC primase
DnaG primase
DnaI helicase
Explanation - DnaG primase synthesizes short RNA primers needed for DNA replication initiation.
Correct answer is: DnaG primase
Q.60 What is the effect of a frameshift mutation on a protein coding sequence?
It changes one amino acid
It introduces a premature stop codon
It changes the reading frame for all downstream codons
It has no effect
Explanation - A frameshift alters the grouping of codons, changing the entire downstream amino acid sequence.
Correct answer is: It changes the reading frame for all downstream codons
Q.61 Which bacterial regulatory system controls the expression of virulence genes in response to host signals?
Quorum sensing
SOS response
Ribosome binding
DNA repair
Explanation - Quorum sensing allows bacteria to detect population density and regulate virulence gene expression.
Correct answer is: Quorum sensing
Q.62 The 'recA' gene in E. coli is involved in:
Protein synthesis
DNA repair and homologous recombination
Transcription termination
RNA splicing
Explanation - recA promotes strand exchange during homologous recombination and DNA repair.
Correct answer is: DNA repair and homologous recombination
Q.63 What is a 'transposase' enzyme primarily responsible for?
Binding to promoter regions
Excising and inserting transposable elements
Synthesizing RNA
Repairing DNA breaks
Explanation - Transposase catalyzes the cut-and-paste or copy-and-paste movement of transposons.
Correct answer is: Excising and inserting transposable elements
Q.64 Which of the following best describes a 'promoter-proximal pausing' event?
RNA polymerase pauses shortly after initiation
DNA polymerase pauses during replication
Transposase pauses before excising transposons
Ligase pauses during ligation
Explanation - Promoter-proximal pausing occurs when RNA polymerase temporarily halts near the promoter during transcription initiation.
Correct answer is: RNA polymerase pauses shortly after initiation
Q.65 In bacterial genetics, a 'fitness trade-off' often occurs when:
A cell gains a plasmid that confers antibiotic resistance but grows slower
A cell replicates its DNA faster
A cell synthesizes more ribosomes
A cell forms spores
Explanation - Acquiring new genetic material can impose a metabolic burden, reducing growth rate.
Correct answer is: A cell gains a plasmid that confers antibiotic resistance but grows slower
Q.66 Which of the following is a hallmark of the SOS response?
Downregulation of DNA repair genes
Upregulation of error-prone DNA polymerases
Inactivation of ribosomal RNA
Activation of protein folding pathways
Explanation - The SOS response induces error-prone polymerases like Pol V to bypass lesions.
Correct answer is: Upregulation of error-prone DNA polymerases
Q.67 The term 'codon usage bias' refers to:
The tendency of genes to use rare codons
The preference for certain codons over others for the same amino acid
The inability to change codons
The use of only stop codons
Explanation - Codon usage bias reflects selection for efficient translation and gene expression.
Correct answer is: The preference for certain codons over others for the same amino acid
Q.68 Which bacterial enzyme repairs mismatches after DNA replication by excising the incorrect strand?
DNA polymerase I
Exonuclease
Mismatch repair endonuclease
Ligase
Explanation - The endonuclease recognizes mismatches and cleaves the DNA, allowing repair synthesis.
Correct answer is: Mismatch repair endonuclease
Q.69 During homologous recombination, the protein RecBCD initiates:
Strand invasion
DNA unwinding
Methylation
Transcription termination
Explanation - RecBCD processes DNA ends and unwinds the duplex to facilitate strand exchange.
Correct answer is: DNA unwinding
Q.70 Which of these is a key advantage of using bacterial systems for recombinant protein production?
High-level eukaryotic post-translational modifications
Rapid growth and easy genetic manipulation
Low cost of media
Inability to express toxic proteins
Explanation - Bacteria grow fast, are cheap to culture, and are genetically tractable for recombinant protein expression.
Correct answer is: Rapid growth and easy genetic manipulation
Q.71 The 'oriT' site on a conjugative plasmid is essential for:
Initiating transcription
Replication initiation
Plasmid transfer during conjugation
Protein synthesis
Explanation - OriT is the origin of transfer where relaxase nicks to start plasmid conjugation.
Correct answer is: Plasmid transfer during conjugation
Q.72 In bacterial conjugation, the 'tra' genes encode:
Ribosomal proteins
Conjugation machinery including the pilus
Transcription factors
DNA repair enzymes
Explanation - Tra genes encode proteins required for pilus formation and DNA transfer during conjugation.
Correct answer is: Conjugation machinery including the pilus
Q.73 Which type of mutation changes the amino acid but not the codon due to the genetic code redundancy?
Missense mutation
Silent mutation
Nonsense mutation
Frameshift mutation
Explanation - Silent mutations alter the DNA sequence but encode the same amino acid due to codon redundancy.
Correct answer is: Silent mutation
Q.74 The 'ftsZ' protein in bacteria is essential for:
DNA replication
Cell division septum formation
Protein synthesis
Metabolism
Explanation - ftsZ encodes a tubulin-like protein that forms a contractile ring during cytokinesis.
Correct answer is: Cell division septum formation
Q.75 Which bacterial gene product is directly involved in the formation of the bacterial flagellum?
MotA
FliC
RecA
DnaK
Explanation - FliC encodes the flagellin protein that polymerizes to form the flagellar filament.
Correct answer is: FliC
Q.76 Which of the following best defines an 'allele' in bacterial genetics?
A protein encoded by a gene
A variant form of a gene at a specific locus
A type of plasmid
An enzyme that repairs DNA
Explanation - Alleles are different versions of the same gene that may produce distinct phenotypes.
Correct answer is: A variant form of a gene at a specific locus
Q.77 What is the primary role of the 'lacI' gene product?
To activate transcription in the presence of lactose
To repress the lac operon in the absence of lactose
To degrade lactose
To synthesize ribosomes
Explanation - LacI encodes a repressor that binds to the operator when lactose is absent to block transcription.
Correct answer is: To repress the lac operon in the absence of lactose
Q.78 The term 'genome plasticity' in bacteria refers to:
The ability of the genome to change via mutations, recombination, and horizontal gene transfer
The rigidity of bacterial genomes
The inability to adapt to environments
The presence of only a single chromosome
Explanation - Genome plasticity allows bacteria to evolve quickly by altering their genetic content.
Correct answer is: The ability of the genome to change via mutations, recombination, and horizontal gene transfer
Q.79 Which of the following best describes a 'bacteriophage'?
A bacterial cell that produces toxins
A virus that infects bacteria
An enzyme that repairs DNA
A plasmid that carries antibiotic resistance
Explanation - Bacteriophages are viruses that specifically infect bacterial hosts.
Correct answer is: A virus that infects bacteria
Q.80 What is the function of the 'Pol III' enzyme in bacterial DNA replication?
Initiating replication
Elongating the new DNA strand with high fidelity
Repairing mismatches
Transcribing RNA
Explanation - Pol III is the primary polymerase for DNA synthesis during replication.
Correct answer is: Elongating the new DNA strand with high fidelity
Q.81 The 'csp' genes in bacteria encode:
Cold shock proteins
Cell surface proteins
Conjugation factors
Cryptic plasmids
Explanation - csp genes produce proteins that help bacteria respond to low temperature stress.
Correct answer is: Cold shock proteins
Q.82 Which type of mutation introduces an extra adenine in the DNA sequence?
Insertion
Deletion
Substitution
Translocation
Explanation - Insertion adds one or more nucleotides, such as an extra adenine, into the sequence.
Correct answer is: Insertion
Q.83 The 'SfiI' restriction enzyme recognizes which DNA sequence?
5'-CCANNNNNNTGG-3'
5'-GAATTC-3'
5'-GGATCC-3'
5'-TATAAA-3'
Explanation - SfiI is a type IIs restriction enzyme with the specified recognition sequence.
Correct answer is: 5'-CCANNNNNNTGG-3'
Q.84 The 'gyrA' gene in E. coli is responsible for:
Synthesizing DNA gyrase subunit A
Regulating gene expression
Repairing DNA damage
Transcription of ribosomal RNA
Explanation - gyrA encodes one subunit of DNA gyrase, a type II topoisomerase.
Correct answer is: Synthesizing DNA gyrase subunit A
Q.85 Which of the following is an example of a 'plasmid shuttle vector'?
pUC19
pBR322
pCR2.1
pET28a
Explanation - pET28a is a vector designed for expression in both E. coli and eukaryotic cells.
Correct answer is: pET28a
Q.86 Which bacterial protein is involved in DNA mismatch repair by recognizing G-T mismatches?
MutS
MutL
MutH
RecA
Explanation - MutS binds to mismatched base pairs and initiates repair.
Correct answer is: MutS
Q.87 What does the 'oriV' sequence on a plasmid indicate?
Origin of transcription
Origin of replication
Origin of transfer
Origin of translation
Explanation - oriV is the site where plasmid DNA replication begins.
Correct answer is: Origin of replication
Q.88 Which of the following best describes the 'CRISPR array' in bacterial genomes?
A series of short repeated sequences interspersed with spacer sequences
A continuous gene coding for DNA polymerase
A region that codes for ribosomal proteins
A locus for antibiotic resistance genes
Explanation - The CRISPR array contains repeats and spacers derived from phage DNA, forming part of the adaptive immune system.
Correct answer is: A series of short repeated sequences interspersed with spacer sequences
Q.89 In the context of bacterial genetics, the 'gene dosage effect' refers to:
The number of copies of a gene influencing the level of its expression
The speed of DNA replication
The rate of protein degradation
The frequency of mutations
Explanation - Having more copies of a gene often leads to higher expression levels.
Correct answer is: The number of copies of a gene influencing the level of its expression
Q.90 Which bacterial gene product is a component of the RNA polymerase holoenzyme that recognizes the -10 promoter region?
sigma factor σ70
alpha subunit
beta subunit
beta prime subunit
Explanation - σ70 directs RNA polymerase to the -10 promoter region for transcription initiation.
Correct answer is: sigma factor σ70
Q.91 Which of the following is a key feature of 'phase variation' in bacterial pathogens?
Random changes in DNA replication timing
Alternating expression of surface antigens to evade immunity
Permanent mutation of the antibiotic resistance gene
Stochastic variation in metabolic enzyme production
Explanation - Phase variation allows bacteria to switch surface antigens on or off to avoid immune detection.
Correct answer is: Alternating expression of surface antigens to evade immunity
Q.92 Which of the following processes is required for the integration of a phage genome into the bacterial chromosome?
Site-specific recombination mediated by integrase
Random insertion by transposase
Homologous recombination of plasmids
DNA excision by RecA
Explanation - Integrase catalyzes recombination at specific attachment sites to integrate the prophage.
Correct answer is: Site-specific recombination mediated by integrase
Q.93 Which of the following bacterial enzymes is involved in repairing double-strand breaks via homologous recombination?
RecA
Ligase
RNA polymerase
DNA ligase
Explanation - RecA facilitates strand exchange during homologous recombination to repair double-strand breaks.
Correct answer is: RecA
Q.94 The 'lacZ' reporter gene is commonly used in bacterial genetics because it:
Produces a visible color change in the presence of X-gal
Encodes a fluorescent protein
Inhibits plasmid replication
Suppresses antibiotic resistance
Explanation - Beta-galactosidase encoded by lacZ cleaves X-gal to produce a blue pigment, indicating gene expression.
Correct answer is: Produces a visible color change in the presence of X-gal
Q.95 In bacterial genetics, a 'plasmid shuttle vector' is designed to:
Replicate only in bacterial cells
Replicate in both bacterial and eukaryotic cells
Act as a phage
Serve as a restriction enzyme
Explanation - Shuttle vectors contain origins of replication compatible with multiple host systems.
Correct answer is: Replicate in both bacterial and eukaryotic cells
Q.96 Which of the following best describes the 'SOS regulon' in E. coli?
Genes that are turned off during stress
Genes that are upregulated during DNA damage response
Genes involved in photosynthesis
Genes that encode ribosomal proteins
Explanation - The SOS regulon includes DNA repair and error-prone polymerase genes activated during damage.
Correct answer is: Genes that are upregulated during DNA damage response
Q.97 Which bacterial protein is directly involved in the formation of the bacterial capsule?
Capsule synthase (Cps)
RecA
LacZ
DnaK
Explanation - Cps enzymes synthesize the polysaccharide capsule that surrounds many bacterial cells.
Correct answer is: Capsule synthase (Cps)
Q.98 What is the primary role of the 'ftsZ' gene in bacterial cell division?
Encodes a DNA replication initiator
Forms the contractile ring for cytokinesis
Encodes a plasmid replication protein
Regulates antibiotic resistance
Explanation - FtsZ polymerizes to form the Z-ring that constricts during bacterial cell division.
Correct answer is: Forms the contractile ring for cytokinesis
Q.99 Which bacterial process is essential for the replication of plasmids with a low copy number?
Rolling-circle replication
θ replication
Recombination-mediated replication
Transcriptional coupling
Explanation - Low-copy plasmids often use rolling-circle replication to maintain their numbers.
Correct answer is: Rolling-circle replication
Q.100 The 'rpoB' gene in bacteria encodes a subunit of which enzyme?
DNA polymerase
RNA polymerase beta subunit
Ligase
Helicase
Explanation - rpoB encodes the beta subunit of RNA polymerase, a target for certain antibiotics.
Correct answer is: RNA polymerase beta subunit
Q.101 Which of the following is a feature of 'phase variation' that allows bacteria to evade the host immune system?
Randomly switching between different metabolic states
Stochastic expression of virulence genes
On/off switching of surface antigen genes
Constant expression of all surface proteins
Explanation - Phase variation allows bacteria to alternately express or silence surface antigens to avoid detection.
Correct answer is: On/off switching of surface antigen genes
Q.102 In bacterial genetics, what is an 'allelic exchange' commonly used for?
Creating a plasmid library
Introducing a specific mutation into a chromosome
Removing a plasmid from the cell
Repairing DNA double-strand breaks
Explanation - Allelic exchange replaces an endogenous allele with a mutant version via homologous recombination.
Correct answer is: Introducing a specific mutation into a chromosome
Q.103 Which enzyme is required to repair UV-induced cyclobutane pyrimidine dimers?
Photolyase
DNA polymerase
Ligase
RNA polymerase
Explanation - Photolyase uses light energy to reverse cyclobutane pyrimidine dimers formed by UV exposure.
Correct answer is: Photolyase
Q.104 What does the 'oriC' region in bacterial chromosomal DNA represent?
Origin of transcription
Origin of replication
Origin of transfer
Origin of translation
Explanation - OriC is the specific DNA sequence where replication of the bacterial chromosome initiates.
Correct answer is: Origin of replication
Q.105 Which bacterial enzyme is responsible for unwinding the DNA duplex at the replication fork?
Helicase
DNA polymerase
Ligase
Transposase
Explanation - Helicase separates the two strands of DNA to allow replication machinery access.
Correct answer is: Helicase
Q.106 The 'lacZ' gene product, beta-galactosidase, is commonly used in bacterial genetics because it:
Is fluorescent under UV light
Produces a blue color with X-gal
Blocks plasmid replication
Inhibits antibiotic resistance genes
Explanation - Beta-galactosidase cleaves X-gal to yield a blue pigment, marking colonies that express the gene.
Correct answer is: Produces a blue color with X-gal
Q.107 Which of the following best describes a 'promoter' in bacterial genetics?
A protein that synthesizes RNA
A DNA sequence where RNA polymerase binds to initiate transcription
An enzyme that repairs mismatches
A plasmid replication origin
Explanation - Promoters provide binding sites for RNA polymerase and its sigma factor.
Correct answer is: A DNA sequence where RNA polymerase binds to initiate transcription
Q.108 In bacterial conjugation, the gene cluster 'tra' is responsible for:
Encoding antibiotic resistance proteins
Assembling the pilus and conjugation machinery
Synthesizing ribosomal proteins
Repairing DNA damage
Explanation - Tra genes encode components essential for the formation of the conjugation pilus and DNA transfer.
Correct answer is: Assembling the pilus and conjugation machinery
Q.109 Which of the following is a key feature of the CRISPR-Cas immune system in bacteria?
It uses ribosomal RNA to target phages
It stores short sequences from phages to target them for degradation
It relies on plasmids to provide immunity
It is only found in archaea
Explanation - CRISPR arrays store spacers derived from phage DNA, guiding Cas proteins to recognize and cut matching sequences.
Correct answer is: It stores short sequences from phages to target them for degradation
Q.110 Which bacterial gene product is essential for the synthesis of the peptidoglycan layer?
MurA
RecA
LacZ
DnaK
Explanation - MurA initiates peptidoglycan biosynthesis by converting UDP-N-acetylglucosamine to a key precursor.
Correct answer is: MurA
Q.111 A 'knockout mutant' in bacterial genetics refers to:
A strain with an extra copy of a gene
A strain where a specific gene is deleted or inactivated
A strain that overexpresses a gene
A strain with no genetic modifications
Explanation - Knockout mutants lack functional copies of target genes to study gene function.
Correct answer is: A strain where a specific gene is deleted or inactivated