Q.1 Which enzyme is essential for joining the ends of two DNA fragments during recombinant DNA construction?
DNA polymerase
DNA ligase
RNA polymerase
Helicase
Explanation - DNA ligase catalyzes the formation of phosphodiester bonds between DNA fragments, sealing nicks in the sugar‑phosphate backbone.
Correct answer is: DNA ligase
Q.2 What is the main function of a plasmid in recombinant DNA technology?
To replicate the host genome
To serve as a vector for foreign DNA
To produce proteins directly
To degrade unwanted RNA
Explanation - A plasmid acts as a small, circular DNA vector that can carry and propagate foreign DNA within a host cell.
Correct answer is: To serve as a vector for foreign DNA
Q.3 Which restriction enzyme cuts the DNA at the sequence 5’–GAATTC–3’?
EcoRI
BamHI
HindIII
NdeI
Explanation - EcoRI recognizes the palindromic sequence GAATTC and cleaves between G and A, creating sticky ends.
Correct answer is: EcoRI
Q.4 During ligation, what cofactor is required for DNA ligase activity?
ATP
GTP
FAD
CoA
Explanation - DNA ligase requires ATP to phosphorylate the 5' end of DNA, facilitating the formation of a phosphodiester bond.
Correct answer is: ATP
Q.5 Which technique is commonly used to separate DNA fragments by size?
Northern blotting
Southern blotting
Western blotting
Agarose gel electrophoresis
Explanation - Agarose gel electrophoresis separates DNA fragments based on size as they migrate through the gel matrix under an electric field.
Correct answer is: Agarose gel electrophoresis
Q.6 What is the purpose of an antibiotic resistance gene in a plasmid vector?
To encode a toxin for selection
To confer resistance to an antibiotic for selection
To increase plasmid copy number
To facilitate plasmid replication
Explanation - The antibiotic resistance gene allows transformed cells to grow only when the plasmid is present, facilitating selection.
Correct answer is: To confer resistance to an antibiotic for selection
Q.7 Which of the following is NOT a common type of restriction enzyme?
Type I
Type II
Type III
Type IV
Explanation - Restriction enzymes are categorized as Type I, II, and III. Type IV enzymes recognize and cut methylated DNA.
Correct answer is: Type IV
Q.8 What is a 'clone' in the context of recombinant DNA?
A cell with a plasmid that has integrated into the genome
A bacterial colony that contains many identical plasmids
A DNA fragment that has been mutated
A protein that is produced in large amounts
Explanation - In molecular biology, a clone refers to a population of cells that all contain the same plasmid construct.
Correct answer is: A bacterial colony that contains many identical plasmids
Q.9 What is the role of the origin of replication (ori) in a plasmid?
It codes for antibiotic resistance
It determines the plasmid’s copy number
It is the site where plasmid replication begins
It acts as a promoter for gene expression
Explanation - The ori is a specific DNA sequence where the replication machinery initiates plasmid DNA synthesis.
Correct answer is: It is the site where plasmid replication begins
Q.10 Which method is used to confirm the presence of a recombinant plasmid in transformed cells?
PCR amplification of the inserted gene
Enzyme-linked immunosorbent assay (ELISA)
Mass spectrometry
Flow cytometry
Explanation - PCR can amplify the inserted gene from plasmid DNA, confirming its presence in transformed cells.
Correct answer is: PCR amplification of the inserted gene
Q.11 What is the function of a promoter in a plasmid construct?
To initiate DNA replication
To bind the plasmid to the host genome
To control transcription of inserted genes
To enhance plasmid stability
Explanation - A promoter provides a binding site for RNA polymerase, initiating transcription of the downstream gene.
Correct answer is: To control transcription of inserted genes
Q.12 Which of the following describes 'bacterial artificial chromosome' (BAC)?
A small plasmid that replicates at low copy number
A large plasmid used for cloning large DNA fragments
A viral vector used in gene therapy
An artificial chromosome that can replace the human chromosome
Explanation - BACs are engineered plasmids that can carry inserts up to 300 kb, enabling cloning of large genomic regions.
Correct answer is: A large plasmid used for cloning large DNA fragments
Q.13 Which enzyme is required to synthesize the RNA strand from a DNA template during transcription?
DNA polymerase I
DNA polymerase II
RNA polymerase
Reverse transcriptase
Explanation - RNA polymerase catalyzes the synthesis of RNA by incorporating ribonucleotides complementary to DNA.
Correct answer is: RNA polymerase
Q.14 In recombinant DNA technology, what does 'in vitro' mean?
Inside a living cell
Outside a living organism or cell
Within a laboratory animal
Within a viral particle
Explanation - "In vitro" refers to experiments performed in a controlled environment outside of living tissues.
Correct answer is: Outside a living organism or cell
Q.15 Which of the following is a common host organism for plasmid replication?
E. coli
S. cerevisiae
A. thaliana
H. sapiens
Explanation - E. coli is the most widely used bacterial host for cloning plasmids due to its fast growth and well‑characterized genetics.
Correct answer is: E. coli
Q.16 What does a 'blue-white screening' system detect?
The presence of an antibiotic resistance marker
The activity of beta‑galactosidase indicating plasmid insertion
The expression level of a reporter gene
The plasmid copy number
Explanation - Blue-white screening uses the lacZ gene; disruption of lacZ by an insert produces white colonies, while intact lacZ gives blue colonies.
Correct answer is: The activity of beta‑galactosidase indicating plasmid insertion
Q.17 Which of the following is NOT a step in the recombinant DNA workflow?
DNA extraction
PCR amplification
Protein purification
Transformation
Explanation - Protein purification is part of downstream protein expression, not an essential step in creating recombinant DNA.
Correct answer is: Protein purification
Q.18 Which of the following best describes 'site‑directed mutagenesis'?
Randomly mutating DNA fragments
Introducing specific mutations at a particular site in DNA
Amplifying a gene to increase its copy number
Removing a gene from the plasmid
Explanation - Site‑directed mutagenesis allows precise changes at a chosen location, enabling functional studies of genes.
Correct answer is: Introducing specific mutations at a particular site in DNA
Q.19 Which enzyme is responsible for removing the 5’ cap from mRNA?
Capping enzyme
Decapping enzyme
Poly(A) polymerase
Exonuclease
Explanation - Decapping enzymes remove the 5' cap to initiate mRNA degradation or translation regulation.
Correct answer is: Decapping enzyme
Q.20 What does the term 'codon' refer to in DNA or RNA sequences?
A single nucleotide
A sequence of three nucleotides
An enzyme that synthesizes proteins
A region of the plasmid controlling replication
Explanation - A codon comprises three nucleotides and codes for one amino acid during translation.
Correct answer is: A sequence of three nucleotides
Q.21 Which of the following is a function of a selectable marker gene?
To fluorescently label cells
To provide antibiotic resistance for selection
To degrade plasmid DNA
To inhibit replication
Explanation - Selectable markers allow researchers to identify cells that have successfully taken up the plasmid.
Correct answer is: To provide antibiotic resistance for selection
Q.22 Which enzyme synthesizes a complementary DNA strand during replication?
RNA polymerase
DNA polymerase
Ligase
Helicase
Explanation - DNA polymerase adds nucleotides to the growing DNA strand, forming a complementary copy.
Correct answer is: DNA polymerase
Q.23 What is the role of a terminator sequence in a plasmid?
To start transcription
To stop transcription
To initiate plasmid replication
To increase plasmid stability
Explanation - A terminator signals RNA polymerase to cease transcription, preventing read‑through of downstream genes.
Correct answer is: To stop transcription
Q.24 Which of these plasmids is known for having a high copy number in E. coli?
pBR322
pUC19
pGEX-4T-1
pET28a
Explanation - pUC19 is engineered for a high copy number (~500–1000 copies per cell), enhancing plasmid yield.
Correct answer is: pUC19
Q.25 In the context of recombinant DNA, what does 'restriction enzyme' refer to?
An enzyme that repairs DNA
An enzyme that cuts DNA at specific sequences
An enzyme that synthesizes proteins
An enzyme that removes RNA
Explanation - Restriction enzymes recognize specific DNA sequences and cleave the DNA, creating fragments for cloning.
Correct answer is: An enzyme that cuts DNA at specific sequences
Q.26 What does the acronym 'PCR' stand for?
Polymerase Chain Reaction
Protein Chromatin Reaction
Polymerase Crossover Reaction
Protein Chain Repression
Explanation - PCR is a technique that amplifies specific DNA fragments by repeated cycles of denaturation, annealing, and extension.
Correct answer is: Polymerase Chain Reaction
Q.27 Which of the following is a common host cell used for producing recombinant proteins in eukaryotic systems?
E. coli
S. cerevisiae
B. subtilis
L. lactis
Explanation - Saccharomyces cerevisiae (yeast) is a eukaryotic host that can perform post‑translational modifications.
Correct answer is: S. cerevisiae
Q.28 Which of the following best describes 'gene knock‑in'?
Deleting a gene from the genome
Introducing a new gene into a specific genomic locus
Silencing a gene's expression
Duplicating a gene within the genome
Explanation - Gene knock‑in replaces or inserts a gene at a defined site, often to study gene function.
Correct answer is: Introducing a new gene into a specific genomic locus
Q.29 What is the function of the 'lacZ' gene in cloning vectors?
To confer antibiotic resistance
To produce beta‑galactosidase for blue‑white screening
To enhance plasmid replication
To code for a fluorescent protein
Explanation - lacZ encodes beta‑galactosidase; disruption of this gene by an insert results in white colonies in blue‑white screening.
Correct answer is: To produce beta‑galactosidase for blue‑white screening
Q.30 Which enzyme is used to synthesize complementary DNA (cDNA) from an RNA template?
DNA polymerase I
DNA polymerase II
DNA polymerase III
Reverse transcriptase
Explanation - Reverse transcriptase converts RNA into double‑stranded DNA, enabling cloning of expressed genes.
Correct answer is: Reverse transcriptase
Q.31 What is the primary role of a 'promoter' in a plasmid?
To bind RNA polymerase and start transcription
To bind DNA polymerase and start replication
To act as a terminator
To increase plasmid copy number
Explanation - Promoters contain specific DNA motifs recognized by RNA polymerase to initiate transcription of downstream genes.
Correct answer is: To bind RNA polymerase and start transcription
Q.32 Which of the following plasmids is commonly used as a shuttle vector between bacteria and yeast?
pUC19
pBR322
pRS426
pGEX-4T-1
Explanation - pRS426 contains elements allowing replication in both E. coli and Saccharomyces cerevisiae.
Correct answer is: pRS426
Q.33 Which of these is a direct product of transcription?
mRNA
tRNA
rRNA
Protein
Explanation - Transcription produces messenger RNA (mRNA), which is later translated into protein.
Correct answer is: mRNA
Q.34 During a ligation reaction, which buffer component is essential for enzyme activity?
Tris-HCl
MgCl2
NaCl
Tween-20
Explanation - Mg^2+ ions are required cofactor for ligase activity, stabilizing the DNA ends and catalyzing bond formation.
Correct answer is: MgCl2
Q.35 In a restriction digest, what determines the size of the DNA fragments produced?
The length of the DNA template
The number of restriction sites
The type of polymerase used
The temperature of the reaction
Explanation - Each cut creates fragments whose lengths depend on the distances between restriction enzyme recognition sites.
Correct answer is: The number of restriction sites
Q.36 Which of the following plasmid features ensures that the plasmid does not integrate into the host chromosome?
Origin of replication
Selectable marker
Terminal repeat
LacZ gene
Explanation - An ori allows plasmid replication autonomously; without integration signals, the plasmid remains extrachromosomal.
Correct answer is: Origin of replication
Q.37 What is a 'restriction fragment length polymorphism' (RFLP)?
A variation in DNA sequence causing different restriction site patterns
A method to amplify DNA fragments
A type of PCR mutation
A method of protein purification
Explanation - RFLP analysis detects genetic variation by comparing sizes of restriction fragments from different individuals.
Correct answer is: A variation in DNA sequence causing different restriction site patterns
Q.38 Which enzyme is used to remove the 3' phosphate group from a DNA strand during repair?
DNA polymerase I
DNA ligase
DNA polymerase II
DNA polymerase III
Explanation - DNA polymerase I has 5'→3' exonuclease activity and removes 3' phosphate groups during repair.
Correct answer is: DNA polymerase I
Q.39 Which of the following is a characteristic of a 'low copy number' plasmid?
It replicates in thousands of copies per cell
It replicates in only a few copies per cell
It cannot be maintained in E. coli
It does not require an antibiotic marker
Explanation - Low copy number plasmids maintain a limited number of copies, often used to express toxic genes.
Correct answer is: It replicates in only a few copies per cell
Q.40 What is the main advantage of using a 'high copy number' plasmid for protein expression?
It reduces metabolic burden
It increases plasmid stability
It provides more DNA template for transcription
It eliminates the need for selection markers
Explanation - Higher plasmid copy number increases the amount of mRNA produced, boosting protein yield.
Correct answer is: It provides more DNA template for transcription
Q.41 Which of the following is NOT a typical component of a plasmid vector map?
Promoter
Origin of replication
Coding sequence
Chromosome
Explanation - A plasmid map shows features of the plasmid; chromosomes are separate, larger DNA elements.
Correct answer is: Chromosome
Q.42 What is the purpose of a 'terminator' in a plasmid?
To start transcription
To stop transcription
To replicate plasmid DNA
To provide antibiotic resistance
Explanation - Terminator sequences signal RNA polymerase to terminate transcription, preventing unwanted read‑through.
Correct answer is: To stop transcription
Q.43 Which enzyme is responsible for removing RNA primers during DNA replication?
DNA polymerase I
DNA polymerase II
DNA polymerase III
Reverse transcriptase
Explanation - DNA polymerase I has 5'→3' exonuclease activity that removes RNA primers on the lagging strand.
Correct answer is: DNA polymerase I
Q.44 Which technique is used to detect specific DNA sequences within a sample?
Northern blotting
Southern blotting
Western blotting
ELISA
Explanation - Southern blotting transfers DNA to a membrane and probes for target sequences with labeled DNA probes.
Correct answer is: Southern blotting
Q.45 What is a 'mutagenesis kit' used for in molecular biology?
To sequence DNA
To introduce mutations at specific positions
To clone plasmids
To purify proteins
Explanation - Mutagenesis kits provide primers and enzymes for site‑directed mutagenesis, creating targeted sequence changes.
Correct answer is: To introduce mutations at specific positions
Q.46 What does 'insertional mutagenesis' involve?
Replacing a gene with another gene
Deleting a gene entirely
Inserting a piece of DNA into a gene to disrupt it
Adding a fluorescent tag to a protein
Explanation - Insertional mutagenesis disrupts gene function by inserting foreign DNA at a target site.
Correct answer is: Inserting a piece of DNA into a gene to disrupt it
Q.47 Which of the following is NOT typically a function of a plasmid?
Providing antibiotic resistance
Encoding a reporter protein
Integrating into the host genome
Replicating independently
Explanation - Most plasmids replicate extrachromosomally; they are not designed to integrate unless engineered.
Correct answer is: Integrating into the host genome
Q.48 Which method is used to determine the sequence of nucleotides in a DNA fragment?
Restriction digest
DNA sequencing
PCR
Gel electrophoresis
Explanation - DNA sequencing determines the exact order of nucleotides in a DNA fragment.
Correct answer is: DNA sequencing
Q.49 What is the main benefit of using a 'shuttle vector'?
It can be transferred between different organisms
It has no antibiotic markers
It replicates only once
It is larger than normal plasmids
Explanation - Shuttle vectors contain origins of replication for multiple hosts, enabling cloning and expression in different species.
Correct answer is: It can be transferred between different organisms
Q.50 Which of the following enzymes is needed for site‑directed recombination in bacterial artificial chromosomes (BACs)?
Cre recombinase
Flp recombinase
Cas9
Ligase
Explanation - Cre recombinase mediates recombination between loxP sites, enabling precise genetic modifications in BACs.
Correct answer is: Cre recombinase
Q.51 What is the purpose of a 'reporter gene' in cloning vectors?
To provide antibiotic resistance
To produce a detectable protein indicating successful cloning
To replicate plasmid DNA
To inhibit host growth
Explanation - Reporter genes (e.g., GFP) allow visual confirmation of gene expression or plasmid presence.
Correct answer is: To produce a detectable protein indicating successful cloning
Q.52 Which of the following is an example of a viral vector used in gene therapy?
E. coli plasmid
AAV vector
Bacterial artificial chromosome
Yeast shuttle vector
Explanation - Adeno‑associated virus (AAV) vectors are widely used for delivering therapeutic genes into human cells.
Correct answer is: AAV vector
Q.53 What type of mutation is introduced by a 'knock‑out' experiment?
A point mutation
An insertion mutation
A deletion of a gene
A duplication of a gene
Explanation - A knock‑out removes or inactivates a gene to study its loss of function.
Correct answer is: A deletion of a gene
Q.54 Which enzyme is responsible for adding a poly(A) tail to pre‑mRNA?
Poly(A) polymerase
RNA polymerase II
DNA polymerase I
Helicase
Explanation - Poly(A) polymerase synthesizes a polyadenylated tail on eukaryotic mRNA, stabilizing it for translation.
Correct answer is: Poly(A) polymerase
Q.55 Which of the following is a characteristic of a 'bacterial artificial chromosome' (BAC) vector?
It carries an origin of replication for E. coli only
It can carry large DNA inserts up to 300 kb
It lacks selectable markers
It replicates in yeast only
Explanation - BACs are designed for cloning large genomic fragments, making them useful for genome mapping.
Correct answer is: It can carry large DNA inserts up to 300 kb
Q.56 What is the purpose of a 'selectable marker' in a plasmid?
To facilitate plasmid replication
To provide an antibiotic resistance gene
To encode a fluorescent protein
To stop transcription
Explanation - Selectable markers allow researchers to identify transformed cells that contain the plasmid by antibiotic selection.
Correct answer is: To provide an antibiotic resistance gene
Q.57 Which enzyme is used to amplify a specific DNA fragment?
DNA ligase
DNA polymerase I
PCR polymerase
RNA polymerase
Explanation - PCR polymerase (often Taq polymerase) synthesizes new DNA strands during PCR cycles.
Correct answer is: PCR polymerase
Q.58 Which of these plasmids has a lacZα fragment used for blue‑white screening?
pUC19
pBR322
pGEM‑T Easy
pET28a
Explanation - pGEM‑T Easy contains an α‑fragment of lacZ for blue‑white screening in E. coli.
Correct answer is: pGEM‑T Easy
Q.59 In a typical cloning experiment, which reagent is used to heat‑shock competent bacterial cells?
Calcium chloride
Magnesium sulfate
Sodium chloride
Potassium chloride
Explanation - CaCl₂ treatment increases cell permeability, enabling DNA uptake during heat shock.
Correct answer is: Calcium chloride
Q.60 Which of the following best describes the 'Golden Gate' cloning method?
A ligation‑based cloning method using Type IIs restriction enzymes
A PCR‑based cloning method using primers with homology arms
A method for generating random mutations
A technique for in‑silico DNA assembly
Explanation - Golden Gate cloning uses Type IIs enzymes that cut outside their recognition sites, enabling scarless assembly.
Correct answer is: A ligation‑based cloning method using Type IIs restriction enzymes
Q.61 What is the primary purpose of the 'T7 promoter' in plasmid constructs?
To provide antibiotic resistance
To drive strong transcription in E. coli with T7 RNA polymerase
To inhibit plasmid replication
To act as a terminator
Explanation - The T7 promoter is recognized by T7 RNA polymerase, enabling high‑level expression of inserted genes.
Correct answer is: To drive strong transcription in E. coli with T7 RNA polymerase
Q.62 Which of the following is a key advantage of using a 'low copy number' plasmid for cloning toxic genes?
It allows rapid growth of host cells
It reduces the risk of plasmid loss
It limits the metabolic burden on host cells
It eliminates the need for selection markers
Explanation - Low copy number plasmids produce fewer copies, reducing stress on cells when expressing toxic proteins.
Correct answer is: It limits the metabolic burden on host cells
Q.63 What is the role of 'intron sequences' in eukaryotic gene expression constructs?
To enhance transcription levels
To provide sites for restriction enzymes
To enable splicing of pre‑mRNA
To function as antibiotic resistance markers
Explanation - Introns are removed during RNA processing; their inclusion can improve expression in eukaryotes.
Correct answer is: To enable splicing of pre‑mRNA
Q.64 Which of the following enzymes is used to generate linear DNA fragments with compatible ends for cloning?
DNA ligase
Restriction enzyme
DNA polymerase I
Reverse transcriptase
Explanation - Restriction enzymes cut DNA at specific sites to produce linear fragments with defined ends.
Correct answer is: Restriction enzyme
Q.65 Which of the following plasmid features allows for high‑level expression of proteins in E. coli?
pUC origin of replication
Strong promoter (e.g., T7)
LacZα fragment
Multiple cloning site only
Explanation - A strong promoter drives abundant transcription, leading to high protein expression.
Correct answer is: Strong promoter (e.g., T7)
Q.66 What does the term 'multiple cloning site' (MCS) refer to in a plasmid?
A region with multiple origins of replication
A stretch of DNA containing several restriction sites
A region coding for multiple proteins
A site for antibiotic selection
Explanation - The MCS contains several unique restriction sites to allow insertion of DNA fragments.
Correct answer is: A stretch of DNA containing several restriction sites
Q.67 Which of these is a typical application of recombinant DNA technology?
Sequencing human DNA
Generating genetically engineered crops
Detecting viral infections
Producing natural dyes
Explanation - Recombinant DNA can be used to introduce desirable traits into plants for agriculture.
Correct answer is: Generating genetically engineered crops
Q.68 What is the purpose of a 'vector backbone' in a plasmid?
To carry the inserted DNA
To provide a framework for replication and selection
To encode the target gene
To provide antibiotic resistance only
Explanation - The backbone contains essential features like ori and selectable markers but no inserted gene.
Correct answer is: To provide a framework for replication and selection
Q.69 Which enzyme is commonly used to convert RNA into cDNA for cloning?
DNA polymerase I
RNA polymerase
Reverse transcriptase
Ligase
Explanation - Reverse transcriptase synthesizes cDNA from an RNA template, enabling cloning of expressed genes.
Correct answer is: Reverse transcriptase
Q.70 What does 'transformation' refer to in molecular biology?
The integration of plasmid DNA into the host genome
The uptake of plasmid DNA by bacterial cells
The expression of foreign proteins
The degradation of DNA by nucleases
Explanation - Transformation is the process by which bacteria take up exogenous plasmid DNA from their environment.
Correct answer is: The uptake of plasmid DNA by bacterial cells
Q.71 Which of these plasmid types is designed for high‑level protein production in yeast?
pUC19
pGEX‑4T‑1
pYES2
pET28a
Explanation - pYES2 contains a galactose‑inducible promoter for protein expression in yeast.
Correct answer is: pYES2
Q.72 Which of the following is a hallmark of a 'minicircle' vector?
It contains only the expression cassette and promoter
It has a large antibiotic resistance gene
It replicates only in bacterial cells
It cannot be packaged into viral particles
Explanation - Minicircles lack bacterial backbone sequences, reducing immunogenicity for therapeutic applications.
Correct answer is: It contains only the expression cassette and promoter
Q.73 Which enzyme is essential for removing RNA primers during lagging‑strand DNA replication?
DNA polymerase I
DNA polymerase II
DNA ligase
Helicase
Explanation - DNA polymerase I has 5'→3' exonuclease activity that degrades RNA primers.
Correct answer is: DNA polymerase I
Q.74 What is the main advantage of using a 'self‑splicing intron' in a cloning vector?
It eliminates the need for selection markers
It allows the removal of unwanted sequences during transcription
It increases plasmid copy number
It enhances plasmid stability
Explanation - Self‑splicing introns can be programmed to remove themselves from transcripts, simplifying gene expression.
Correct answer is: It allows the removal of unwanted sequences during transcription
Q.75 Which of these is a key component of an 'expression cassette' in a plasmid?
Origin of replication
Multiple cloning site
Promoter and coding sequence
Antibiotic resistance gene
Explanation - An expression cassette contains the promoter, coding sequence, and terminator necessary for gene expression.
Correct answer is: Promoter and coding sequence
Q.76 Which of the following enzymes is required to remove the 5' phosphate from a DNA fragment before ligation?
Phosphatase
Kinase
Ligase
Polymerase
Explanation - Phosphatases remove 5' phosphates, preventing self‑ligation of the DNA fragment.
Correct answer is: Phosphatase
Q.77 What is the purpose of an 'origin of transfer' (oriT) in plasmid vectors?
To start plasmid replication
To allow plasmid transfer between bacterial cells via conjugation
To provide antibiotic resistance
To terminate transcription
Explanation - oriT is the site where the transfer of plasmid DNA starts during bacterial conjugation.
Correct answer is: To allow plasmid transfer between bacterial cells via conjugation
Q.78 Which enzyme is used to assemble multiple DNA fragments in a single step using overlapping sequences?
DNA ligase
T4 DNA polymerase
Golden Gate assembly
Overlap PCR
Explanation - Overlap PCR uses overlapping primers to fuse multiple fragments in one PCR reaction.
Correct answer is: Overlap PCR
Q.79 What is the main difference between a plasmid vector and a viral vector?
Plasmids integrate into the host genome, viruses do not
Viruses can package larger DNA fragments than plasmids
Plasmids cannot be used for mammalian gene expression, viruses can
Viruses are used only in bacterial systems
Explanation - Viral vectors can carry larger genomes and efficiently infect eukaryotic cells.
Correct answer is: Viruses can package larger DNA fragments than plasmids
Q.80 Which of these techniques is used to quantify plasmid DNA concentration?
Agarose gel electrophoresis
Spectrophotometry at 260 nm
PCR amplification
Western blot
Explanation - DNA absorbs UV light at 260 nm; measuring absorbance yields DNA concentration.
Correct answer is: Spectrophotometry at 260 nm
Q.81 What is the role of a 'promoter-proximal pausing' in eukaryotic transcription?
To accelerate RNA polymerase progression
To regulate timing of transcription initiation
To terminate transcription prematurely
To enhance translation efficiency
Explanation - Promoter-proximal pausing controls gene expression by delaying RNA polymerase release into productive elongation.
Correct answer is: To regulate timing of transcription initiation
Q.82 Which of the following best describes a 'phage display' system?
Displaying proteins on bacterial cell surfaces
Using bacteriophages to display peptides on their coat proteins for screening
Displaying DNA fragments inside phage capsids
Using phages to deliver plasmids into mammalian cells
Explanation - Phage display presents foreign peptides on phage proteins, allowing selection of high‑affinity binders.
Correct answer is: Using bacteriophages to display peptides on their coat proteins for screening
Q.83 What is a key benefit of using a 'gene gun' for DNA delivery?
It delivers DNA to bacterial cells only
It delivers DNA into plant cells by particle bombardment
It uses viruses for gene delivery
It requires antibiotic selection
Explanation - The gene gun shoots DNA-coated particles into plant tissues, facilitating transformation.
Correct answer is: It delivers DNA into plant cells by particle bombardment
Q.84 Which of the following is a typical outcome of site‑directed mutagenesis using the QuikChange method?
Random mutations throughout the plasmid
A deletion of the entire gene
A specific point mutation at a chosen position
An insertion of a foreign gene
Explanation - QuikChange introduces a precise point mutation via primer design and PCR amplification.
Correct answer is: A specific point mutation at a chosen position
Q.85 What is the function of the 'origin of transfer' (oriT) in bacterial conjugation?
To start plasmid replication
To initiate plasmid transfer between cells
To encode antibiotic resistance
To terminate transcription
Explanation - oriT is the sequence where the nicking enzyme initiates plasmid transfer during conjugation.
Correct answer is: To initiate plasmid transfer between cells
Q.86 Which of the following enzymes is used to add a 5’ cap to eukaryotic mRNA during capping?
Capping enzyme
Decapping enzyme
Poly(A) polymerase
Ligase
Explanation - The capping enzyme transfers a 7-methylguanosine cap to the 5’ end of nascent mRNA.
Correct answer is: Capping enzyme
Q.87 What does 'gene silencing' by RNA interference (RNAi) involve?
Insertion of a gene into the host genome
Degradation of target mRNA by siRNA
Insertion of a promoter upstream of a gene
Amplification of the target gene
Explanation - RNAi uses small interfering RNAs to guide degradation of specific mRNA transcripts, silencing the gene.
Correct answer is: Degradation of target mRNA by siRNA
Q.88 Which technique allows the precise insertion of a DNA fragment at a specific location within the genome?
Homologous recombination
Random mutagenesis
PCR amplification
Gel electrophoresis
Explanation - Homologous recombination uses sequence homology to target insertion at a defined genomic locus.
Correct answer is: Homologous recombination
Q.89 What is the main purpose of using a 'Bacterial Artificial Chromosome' (BAC) library?
To clone large genomic fragments for genome mapping
To express proteins in mammalian cells
To perform site‑directed mutagenesis
To produce small plasmids for gene therapy
Explanation - BAC libraries store large DNA fragments, enabling detailed genomic analysis.
Correct answer is: To clone large genomic fragments for genome mapping