Q.1 What is the main sugar component of DNA?
Ribose
Deoxyribose
Glucose
Fructose
Explanation - DNA contains deoxyribose as its sugar, whereas RNA contains ribose.
Correct answer is: Deoxyribose
Q.2 Which nitrogenous base is found in both DNA and RNA?
Uracil
Thymine
Adenine
Cytosine
Explanation - Adenine (A) pairs with thymine in DNA and with uracil in RNA, so it is present in both.
Correct answer is: Adenine
Q.3 In DNA, which base pairs with cytosine?
Adenine
Thymine
Guanine
Uracil
Explanation - Cytosine pairs with guanine via three hydrogen bonds.
Correct answer is: Guanine
Q.4 Which type of bond holds the phosphate and sugar together in DNA?
Hydrogen bond
Disulfide bond
Phosphodiester bond
Ionic bond
Explanation - Phosphodiester bonds link the 5’ phosphate to the 3’ hydroxyl of the sugar backbone.
Correct answer is: Phosphodiester bond
Q.5 What is the shape of a single-stranded RNA molecule?
Double helix
Coiled rope
Coiled single strand
Straight line
Explanation - RNA is typically single-stranded and can fold into secondary structures.
Correct answer is: Coiled single strand
Q.6 Which enzyme initiates DNA replication by unwinding the helix?
DNA polymerase
Helicase
Ligase
Topoisomerase
Explanation - Helicase unwinds the double helix, creating replication forks.
Correct answer is: Helicase
Q.7 During transcription, the RNA sequence is complementary to which DNA strand?
Coding strand
Template strand
Both strands
Neither strand
Explanation - RNA polymerase reads the template strand and synthesizes RNA complementary to it.
Correct answer is: Template strand
Q.8 Which polymerase is responsible for synthesizing the lagging strand during DNA replication?
DNA polymerase I
DNA polymerase III
RNA polymerase II
DNA polymerase β
Explanation - In E. coli, DNA polymerase III primarily synthesizes both leading and lagging strands.
Correct answer is: DNA polymerase III
Q.9 What is the function of the 5’ cap added to eukaryotic mRNA?
To provide energy for translation
To protect mRNA from degradation
To serve as a binding site for ribosomes
Both B and C
Explanation - The 5’ cap protects mRNA and facilitates ribosome binding during translation.
Correct answer is: Both B and C
Q.10 Which codon signals the start of translation in most organisms?
UAA
UAG
UGA
AUG
Explanation - AUG codes for methionine and serves as the start codon for translation.
Correct answer is: AUG
Q.11 The genetic code is considered to be:
Universal, degenerate, and redundant
Universal, non-degenerate, and redundant
Non-universal, degenerate, and redundant
Universal, degenerate, and non-redundant
Explanation - The genetic code is nearly universal, degenerate (multiple codons per amino acid), and redundant.
Correct answer is: Universal, degenerate, and redundant
Q.12 Which enzyme removes RNA primers during DNA replication in prokaryotes?
DNA polymerase I
DNA ligase
RNA polymerase
Helicase
Explanation - DNA polymerase I in E. coli has 5’→3’ exonuclease activity to remove primers.
Correct answer is: DNA polymerase I
Q.13 What is the main difference between mRNA splicing in eukaryotes and prokaryotes?
Eukaryotes splice introns out
Prokaryotes splice introns out
Only eukaryotes add a 5’ cap
Only prokaryotes add a 3’ poly-A tail
Explanation - Eukaryotic pre-mRNA contains introns that are removed via splicing.
Correct answer is: Eukaryotes splice introns out
Q.14 Which type of RNA carries amino acids to the ribosome during translation?
mRNA
tRNA
rRNA
siRNA
Explanation - Transfer RNA (tRNA) brings amino acids corresponding to codons on mRNA.
Correct answer is: tRNA
Q.15 Which of the following best describes the Watson-Crick base pairing in DNA?
A pairs with G, C pairs with T
A pairs with T, C pairs with G
A pairs with U, C pairs with G
A pairs with G, C pairs with U
Explanation - Adenine pairs with thymine and cytosine with guanine via hydrogen bonds.
Correct answer is: A pairs with T, C pairs with G
Q.16 During DNA replication, what is the leading strand?
The strand synthesized continuously
The strand synthesized discontinuously
The template strand
The parent strand
Explanation - The leading strand is synthesized in the direction of the replication fork.
Correct answer is: The strand synthesized continuously
Q.17 Which enzyme adds nucleotides to a growing DNA strand in the 5’→3’ direction?
DNA ligase
DNA polymerase
DNA helicase
Topoisomerase
Explanation - DNA polymerase adds nucleotides to the 3’ end of a primer, moving 5’→3’.
Correct answer is: DNA polymerase
Q.18 What is the role of ribosomal RNA (rRNA) in the ribosome?
To provide catalytic activity for peptide bond formation
To carry amino acids
To encode proteins
To act as messenger RNA
Explanation - rRNA constitutes the ribosomal peptidyl transferase center, catalyzing peptide bonds.
Correct answer is: To provide catalytic activity for peptide bond formation
Q.19 Which of the following is NOT a step in the process of transcription?
Initiation
Elongation
Termination
Replication
Explanation - Replication is DNA duplication, not part of transcription.
Correct answer is: Replication
Q.20 Which molecule provides the energy for the synthesis of mRNA during transcription?
ATP
GTP
CTP
All of the above
Explanation - All NTPs contribute energy during RNA synthesis.
Correct answer is: All of the above
Q.21 In eukaryotic cells, where does translation occur?
Nucleus
Mitochondria
Cytoplasm
All of the above
Explanation - Translation happens on ribosomes in the cytoplasm or rough ER.
Correct answer is: Cytoplasm
Q.22 Which of the following best describes the antiparallel nature of DNA strands?
Both strands run in the same direction
The strands run in opposite directions
One strand is circular
Both strands are identical
Explanation - DNA strands are oriented 5’→3’ and 3’→5’, respectively.
Correct answer is: The strands run in opposite directions
Q.23 What is the function of a promoter in gene expression?
To start DNA replication
To initiate transcription
To translate mRNA into protein
To splice introns
Explanation - Promoters are DNA sequences where RNA polymerase binds to begin transcription.
Correct answer is: To initiate transcription
Q.24 Which type of RNA is involved in gene silencing and regulation?
mRNA
tRNA
siRNA
rRNA
Explanation - Small interfering RNA (siRNA) participates in RNA interference.
Correct answer is: siRNA
Q.25 During DNA repair, the enzyme that recognizes and removes damaged nucleotides is:
DNA ligase
DNA polymerase
DNA glycosylase
RNA polymerase
Explanation - DNA glycosylases excise damaged bases during base excision repair.
Correct answer is: DNA glycosylase
Q.26 Which process creates multiple copies of a plasmid within a bacterial cell?
Conjugation
Transduction
Transformation
Replication
Explanation - Plasmid replication occurs within the cell, producing identical copies.
Correct answer is: Replication
Q.27 Which enzyme is responsible for proofreading during DNA replication?
DNA polymerase
DNA ligase
DNA helicase
Topoisomerase
Explanation - DNA polymerase has 3’→5’ exonuclease activity for proofreading.
Correct answer is: DNA polymerase
Q.28 The term 'polymerase chain reaction (PCR)' refers to:
A method to sequence DNA
A method to amplify DNA
A method to measure protein concentration
A method to analyze RNA splicing
Explanation - PCR uses thermal cycling to exponentially amplify specific DNA fragments.
Correct answer is: A method to amplify DNA
Q.29 Which base in RNA replaces thymine found in DNA?
Adenine
Uracil
Cytosine
Guanine
Explanation - RNA contains uracil instead of thymine.
Correct answer is: Uracil
Q.30 Which of the following best describes a gene mutation?
A change in the DNA sequence
An increase in ribosomal activity
An alteration of the RNA polymerase enzyme
A modification of the cell membrane
Explanation - A mutation is a change in the genetic material that can affect function.
Correct answer is: A change in the DNA sequence
Q.31 What is a 'frameshift mutation' caused by?
A single base substitution
Inserting or deleting nucleotides not in multiples of three
Replacing a base with a chemically identical base
Deleting an entire gene
Explanation - Frameshift shifts the reading frame of codons downstream.
Correct answer is: Inserting or deleting nucleotides not in multiples of three
Q.32 Which enzyme in prokaryotes is primarily responsible for sealing nicks between Okazaki fragments?
DNA polymerase I
DNA ligase
RNA polymerase
Helicase
Explanation - DNA ligase joins nicks by forming phosphodiester bonds.
Correct answer is: DNA ligase
Q.33 Which of the following is NOT a component of the ribosome?
Large subunit rRNA
Small subunit rRNA
tRNA
Proteins
Explanation - tRNA is a transfer RNA, not a ribosomal component.
Correct answer is: tRNA
Q.34 Which type of bond connects the nitrogenous bases in a nucleic acid?
Phosphodiester bond
Hydrogen bond
Covalent bond
Ionic bond
Explanation - Base pairing occurs via hydrogen bonds between complementary bases.
Correct answer is: Hydrogen bond
Q.35 Which of the following best describes 'exons'?
Non-coding regions of DNA
Coding regions of DNA that remain in mature mRNA
Regions that code for proteins but are spliced out
Regions involved in DNA replication
Explanation - Exons are the segments retained after splicing.
Correct answer is: Coding regions of DNA that remain in mature mRNA
Q.36 In the genetic code, how many different codons are there for each amino acid on average?
1
2
3
4
Explanation - Because of degeneracy, on average there are about 4 codons per amino acid.
Correct answer is: 4
Q.37 Which process converts an mRNA codon into an amino acid during protein synthesis?
Transcription
Replication
Translation
Splicing
Explanation - Translation reads mRNA codons to synthesize proteins.
Correct answer is: Translation
Q.38 What is the primary function of the 3’ polyadenylated tail on eukaryotic mRNA?
To mark the start of translation
To facilitate ribosome binding
To protect mRNA from degradation and aid export
To signal the end of transcription
Explanation - The poly-A tail enhances mRNA stability and export from nucleus.
Correct answer is: To protect mRNA from degradation and aid export
Q.39 Which of the following is an example of post-translational modification?
DNA replication
mRNA splicing
Protein phosphorylation
RNA editing
Explanation - Phosphorylation occurs after a protein is synthesized.
Correct answer is: Protein phosphorylation
Q.40 The 'central dogma' of molecular biology states that:
DNA → RNA → Protein
Protein → RNA → DNA
RNA → DNA → Protein
Protein → DNA → RNA
Explanation - The central dogma describes the flow of genetic information.
Correct answer is: DNA → RNA → Protein
Q.41 Which of these nucleic acids is a component of the bacterial cell wall?
Peptidoglycan
DNA
RNA
Chitin
Explanation - Peptidoglycan is a polymer that strengthens bacterial walls.
Correct answer is: Peptidoglycan
Q.42 Which enzyme is responsible for unwinding the DNA helix during transcription in eukaryotes?
RNA polymerase II
RNA polymerase I
DNA polymerase
RNA helicase
Explanation - RNA polymerase II transcribes mRNA and unwinds DNA locally.
Correct answer is: RNA polymerase II
Q.43 Which of the following best defines 'gene expression'?
The duplication of DNA strands
The transcription and translation of a gene
The repair of damaged DNA
The synthesis of ribosomal RNA
Explanation - Gene expression involves producing functional products from a gene.
Correct answer is: The transcription and translation of a gene
Q.44 The enzyme that adds nucleotides to a tRNA anticodon is:
Aminoacyl-tRNA synthetase
DNA polymerase
RNA polymerase
Ligase
Explanation - This enzyme charges tRNA with the correct amino acid.
Correct answer is: Aminoacyl-tRNA synthetase
Q.45 Which type of mutation changes a codon but does not alter the encoded amino acid?
Silent mutation
Missense mutation
Nonsense mutation
Frameshift mutation
Explanation - Silent mutations are synonymous changes that preserve the amino acid.
Correct answer is: Silent mutation
Q.46 Which of the following statements about plasmids is FALSE?
They are circular DNA molecules.
They can replicate independently of the bacterial chromosome.
They are present in all bacteria.
They can carry antibiotic resistance genes.
Explanation - Not all bacteria contain plasmids.
Correct answer is: They are present in all bacteria.
Q.47 During DNA replication, the enzyme that removes RNA primers is:
DNA polymerase I
DNA ligase
DNA polymerase III
RNA polymerase
Explanation - DNA polymerase I has 5'→3' exonuclease activity.
Correct answer is: DNA polymerase I
Q.48 Which of these is a characteristic of the eukaryotic nucleus?
It contains ribosomes.
It lacks a nuclear membrane.
It contains nucleolus.
It is the site of DNA replication.
Explanation - The nucleolus is involved in rRNA synthesis.
Correct answer is: It contains nucleolus.
Q.49 What is the main function of the lac operon in E. coli?
To synthesize lactose from glucose
To transport lactose across the cell membrane
To metabolize lactose when glucose is scarce
To degrade lactose into pyruvate
Explanation - The lac operon is induced by lactose presence and absence of glucose.
Correct answer is: To metabolize lactose when glucose is scarce
Q.50 Which of the following is a key difference between prokaryotic and eukaryotic transcription?
Eukaryotes use RNA polymerase I, prokaryotes use RNA polymerase II
Eukaryotic mRNA undergoes capping, polyadenylation, and splicing; prokaryotic mRNA does not
Prokaryotic transcription occurs in the cytoplasm, eukaryotic in the nucleus
Both B and C
Explanation - Eukaryotic mRNA is processed post-transcriptionally, and transcription is nuclear.
Correct answer is: Both B and C
Q.51 In the context of CRISPR-Cas9, what is the role of the guide RNA?
To cut the DNA
To direct the Cas9 enzyme to a specific DNA sequence
To repair DNA after cutting
To bind to the target DNA and form a stable complex
Explanation - Guide RNA pairs with the target DNA to guide Cas9 cleavage.
Correct answer is: To direct the Cas9 enzyme to a specific DNA sequence
Q.52 Which type of RNA carries genetic information from the nucleus to ribosomes in eukaryotic cells?
rRNA
mRNA
tRNA
snRNA
Explanation - mRNA transports the code from DNA to the cytoplasmic ribosome.
Correct answer is: mRNA
Q.53 What is the primary function of the 5’ cap on eukaryotic mRNA?
To protect from ribonucleases
To direct mRNA to mitochondria
To initiate translation by ribosome binding
All of the above
Explanation - The 5’ cap stabilizes mRNA, aids export, and facilitates translation initiation.
Correct answer is: All of the above
Q.54 Which of the following is a common method for detecting DNA mutations in a population?
Gel electrophoresis
DNA sequencing
Northern blotting
Western blotting
Explanation - Sequencing allows identification of base changes across the genome.
Correct answer is: DNA sequencing
Q.55 In the process of replication, which enzyme synthesizes the leading strand first?
DNA polymerase I
DNA polymerase III
Primase
RNA polymerase
Explanation - DNA polymerase III is the main replicative polymerase for both strands.
Correct answer is: DNA polymerase III
Q.56 Which of the following best describes a point mutation?
A deletion of several nucleotides
An insertion of several nucleotides
A single base change
A chromosomal translocation
Explanation - A point mutation affects only one nucleotide.
Correct answer is: A single base change
Q.57 The enzyme that converts mRNA to a complementary DNA (cDNA) is:
DNA polymerase
RNA polymerase
Reverse transcriptase
Ligase
Explanation - Reverse transcriptase synthesizes DNA from an RNA template.
Correct answer is: Reverse transcriptase
Q.58 Which type of bond connects nucleotides in the sugar-phosphate backbone?
Phosphodiester bond
Hydrogen bond
Disulfide bond
Ionic bond
Explanation - Phosphodiester bonds link the 3’ hydroxyl of one sugar to the 5’ phosphate of the next.
Correct answer is: Phosphodiester bond
Q.59 What does 'antisense' mean in relation to nucleic acids?
The strand that pairs with the template during transcription
A strand that encodes proteins
A strand with the opposite polarity to the sense strand
A strand that is not transcribed
Explanation - Antisense is complementary and antiparallel to the sense strand.
Correct answer is: A strand with the opposite polarity to the sense strand
Q.60 Which of the following statements best describes the 3’ to 5’ directionality of DNA?
DNA strands run in the same direction
The 5’ end has a phosphate group, the 3’ end a hydroxyl
The 3’ end has a phosphate group
The 5’ end is where replication begins
Explanation - DNA strand polarity is defined by phosphate at 5’ and hydroxyl at 3’.
Correct answer is: The 5’ end has a phosphate group, the 3’ end a hydroxyl
Q.61 Which enzyme is essential for the initiation of DNA replication at the origin?
DNA ligase
DNA primase
DNA helicase
DNA polymerase III
Explanation - Primase synthesizes a short RNA primer to start DNA synthesis.
Correct answer is: DNA primase
Q.62 In which organelle does mitochondrial DNA replicate?
Mitochondrion
Nucleus
Endoplasmic reticulum
Golgi apparatus
Explanation - Mitochondrial DNA is replicated within the mitochondria.
Correct answer is: Mitochondrion
Q.63 The process by which a DNA template is transcribed into an RNA transcript is called:
Replication
Transcription
Translation
Splicing
Explanation - Transcription converts DNA to RNA.
Correct answer is: Transcription
Q.64 Which of the following is a function of the ribosomal protein L4 in prokaryotes?
Stabilizes the 30S subunit
Forms the exit tunnel for nascent polypeptide
Assists tRNA binding at the A site
Helps in peptide bond formation
Explanation - Ribosomal protein L4 lines the peptide exit tunnel of the large subunit.
Correct answer is: Forms the exit tunnel for nascent polypeptide
Q.65 Which type of mutation changes the reading frame by adding or removing one or more nucleotides?
Missense mutation
Silent mutation
Nonsense mutation
Frameshift mutation
Explanation - Frameshift mutations shift the codon reading frame.
Correct answer is: Frameshift mutation
Q.66 Which of the following is true about the mRNA sequence produced from a DNA template strand?
It is identical to the coding strand
It contains thymine instead of uracil
It is complementary to the template strand
It is reverse complement of the coding strand
Explanation - mRNA is synthesized from the template strand, making it complementary.
Correct answer is: It is complementary to the template strand
Q.67 In prokaryotes, the ribosomal RNA gene cluster is often found in:
Chromosomes
Plasmids
Extrachromosomal elements
Both A and B
Explanation - rRNA genes are typically located on the chromosome, not plasmids.
Correct answer is: Chromosomes
Q.68 Which of the following enzymes is responsible for the removal of mismatched bases during proofreading?
DNA polymerase II
DNA polymerase I
DNA polymerase III
DNA polymerase γ
Explanation - DNA polymerase III has 3'→5' exonuclease activity for proofreading.
Correct answer is: DNA polymerase III
Q.69 What is the key difference between a plasmid and a chromosome?
Plasmids replicate independently; chromosomes do not
Chromosomes are circular; plasmids are linear
Plasmids are only found in eukaryotes
Chromosomes are extrachromosomal elements
Explanation - Plasmids can replicate autonomously, whereas chromosomes require host replication.
Correct answer is: Plasmids replicate independently; chromosomes do not
Q.70 During translation, which ribosomal site receives the tRNA carrying the next amino acid?
A site
P site
E site
T site
Explanation - The A site is where aminoacyl-tRNA binds during elongation.
Correct answer is: A site
Q.71 Which of the following best explains the role of ribosomal RNA (rRNA) in the ribosome?
It forms the peptidyl transferase active site
It transports amino acids to the ribosome
It acts as a messenger for protein synthesis
It serves as a regulatory RNA
Explanation - rRNA provides the catalytic core for peptide bond formation.
Correct answer is: It forms the peptidyl transferase active site
Q.72 Which of these statements correctly describes the function of the 5’ untranslated region (UTR) of mRNA?
It contains the start codon
It is translated into protein
It regulates translation initiation
It encodes a signal peptide
Explanation - The 5’ UTR contains regulatory elements that influence initiation.
Correct answer is: It regulates translation initiation
Q.73 Which enzyme adds a 3’ polyadenylated tail to eukaryotic mRNA?
Poly(A) polymerase
Poly(A) binding protein
RNA ligase
RNA polymerase II
Explanation - Poly(A) polymerase catalyzes addition of adenine residues.
Correct answer is: Poly(A) polymerase
Q.74 The process by which a plasmid is transferred from one bacterial cell to another via direct contact is known as:
Transformation
Transduction
Conjugation
Transcription
Explanation - Conjugation involves direct cell-to-cell transfer through a pilus.
Correct answer is: Conjugation
Q.75 Which of the following is a primary product of the lac operon when lactose is present?
β-galactosidase
Glucose
Lactose
cAMP
Explanation - β-galactosidase breaks down lactose into glucose and galactose.
Correct answer is: β-galactosidase
Q.76 The 'template strand' in DNA refers to:
The strand that is synthesized during replication
The strand used by RNA polymerase to synthesize RNA
The strand that codes for proteins
The strand that is complementary to the mRNA
Explanation - RNA polymerase reads the template strand to produce complementary RNA.
Correct answer is: The strand used by RNA polymerase to synthesize RNA
Q.77 Which type of bond stabilizes the double helix of DNA?
Covalent bonds
Hydrogen bonds
Ionic bonds
Disulfide bonds
Explanation - Base pairs are held by hydrogen bonds between complementary bases.
Correct answer is: Hydrogen bonds
Q.78 During translation, what is the role of the ribosomal P site?
Receives tRNA with the first amino acid
Transfers the growing polypeptide chain
Exits the finished protein
Binds the mRNA codon
Explanation - The P site holds the tRNA linked to the nascent chain.
Correct answer is: Transfers the growing polypeptide chain
Q.79 Which of the following enzymes is responsible for removing RNA primers during DNA replication in mitochondria?
DNA polymerase γ
DNA polymerase I
RNA polymerase III
RNA helicase
Explanation - Mitochondrial DNA replication uses polymerase γ.
Correct answer is: DNA polymerase γ
Q.80 Which process involves the modification of a DNA template to produce an RNA transcript that can be translated into protein?
Replication
Translation
Transcription
Transduction
Explanation - Transcription is the synthesis of RNA from DNA.
Correct answer is: Transcription
Q.81 The process by which a ribosomal subunit is released after the completion of translation is known as:
Termination
Recycling
Initiation
Elongation
Explanation - After termination, ribosomal subunits are recycled for another round.
Correct answer is: Recycling
Q.82 Which of the following is a characteristic of eukaryotic ribosomes?
70S in the cytoplasm
80S in the cytoplasm
60S in the nucleus
70S in mitochondria
Explanation - Eukaryotic cytoplasmic ribosomes are 80S, composed of 60S and 40S subunits.
Correct answer is: 80S in the cytoplasm
Q.83 Which of the following best describes the function of the 3’ untranslated region (UTR) of mRNA?
It contains the stop codon
It regulates mRNA stability and localization
It encodes a signal peptide
It is the region that is translated into protein
Explanation - The 3’ UTR contains regulatory elements affecting mRNA decay.
Correct answer is: It regulates mRNA stability and localization
Q.84 Which of the following best describes a plasmid’s role in antibiotic resistance?
It encodes the antibiotic itself
It carries genes that can be transferred between bacteria
It inhibits DNA replication
It degrades antibiotics
Explanation - Plasmids often carry resistance genes that spread via conjugation.
Correct answer is: It carries genes that can be transferred between bacteria
Q.85 The process by which RNA is synthesized from a DNA template involves:
DNA polymerase
RNA polymerase
DNA ligase
Reverse transcriptase
Explanation - RNA polymerase catalyzes the synthesis of RNA.
Correct answer is: RNA polymerase
Q.86 Which type of mutation results in a premature stop codon?
Missense mutation
Nonsense mutation
Silent mutation
Frameshift mutation
Explanation - A nonsense mutation changes a codon to a stop codon.
Correct answer is: Nonsense mutation
Q.87 The process that involves the addition of a phosphate group to a sugar in the cell membrane is:
Phosphorylation
Polymerization
Hydrolysis
Synthesis
Explanation - Phosphorylation adds a phosphate group to a molecule.
Correct answer is: Phosphorylation
Q.88 Which enzyme is required for the formation of the RNA primer during DNA replication?
DNA polymerase I
Primase
Helicase
Ligase
Explanation - Primase synthesizes a short RNA primer for DNA polymerase to extend.
Correct answer is: Primase
Q.89 Which of the following best describes the difference between a promoter and an enhancer?
Promoters bind RNA polymerase; enhancers increase transcription levels
Enhancers bind RNA polymerase; promoters increase transcription levels
Both are binding sites for RNA polymerase
Promoters are only found in eukaryotes
Explanation - Promoters are core binding sites; enhancers modulate activity.
Correct answer is: Promoters bind RNA polymerase; enhancers increase transcription levels
Q.90 In the context of DNA replication, what is the 'lagging strand'?
The strand synthesized continuously
The strand synthesized discontinuously as Okazaki fragments
The parental strand
The template strand
Explanation - The lagging strand is built in fragments opposite the direction of replication.
Correct answer is: The strand synthesized discontinuously as Okazaki fragments
Q.91 Which of the following statements correctly describes the function of RNA splicing?
It removes introns from pre-mRNA
It adds a 5’ cap to mRNA
It adds a poly-A tail to mRNA
It transcribes DNA into RNA
Explanation - Splicing excises non-coding introns and joins exons.
Correct answer is: It removes introns from pre-mRNA
Q.92 Which type of RNA is directly involved in protein synthesis by carrying amino acids?
mRNA
tRNA
rRNA
snRNA
Explanation - tRNA brings specific amino acids to the ribosome during translation.
Correct answer is: tRNA
Q.93 During PCR, which component is responsible for the initial heating step that denatures the DNA?
DNA polymerase
Primers
Thermal cycler
dNTPs
Explanation - The thermal cycler provides controlled heating and cooling cycles.
Correct answer is: Thermal cycler
Q.94 Which of the following best describes the function of DNA ligase?
Adds nucleotides to a growing DNA strand
Seals nicks between Okazaki fragments
Unwinds DNA helices
Removes RNA primers
Explanation - DNA ligase joins DNA fragments by forming phosphodiester bonds.
Correct answer is: Seals nicks between Okazaki fragments
Q.95 The 'stop codon' in genetic code is also known as:
UAA
AUG
UAG
UGA
Explanation - UAA, UAG, and UGA are all stop codons.
Correct answer is: UAA
Q.96 Which of the following is true regarding the 'template strand' of DNA?
It is the coding strand
It is used as a template for RNA synthesis
It has the same sequence as mRNA
It does not contain uracil
Explanation - The template strand is read by RNA polymerase during transcription.
Correct answer is: It is used as a template for RNA synthesis
Q.97 What is the primary function of the ribosomal small subunit?
Peptidyl transferase activity
Binding the first tRNA
Translocation of tRNA
Binding of mRNA and initiation complex formation
Explanation - The small subunit recognizes the start codon and mRNA sequence.
Correct answer is: Binding of mRNA and initiation complex formation
Q.98 The process of removing RNA primers and filling the gaps with DNA in prokaryotes is carried out by which enzyme?
DNA polymerase I
DNA polymerase III
DNA ligase
RNA polymerase
Explanation - DNA polymerase I has both exonuclease and polymerase activities for primer removal.
Correct answer is: DNA polymerase I
Q.99 Which type of bond links the phosphate groups in the DNA backbone?
Covalent bond
Hydrogen bond
Phosphodiester bond
Ionic bond
Explanation - Phosphodiester bonds link the sugar and phosphate groups.
Correct answer is: Phosphodiester bond
Q.100 In the lac operon, the repressor binds to the operator region when lactose is absent. Which molecule induces the operon when lactose is present?
Allolactose
cAMP
Glucose
ATP
Explanation - Allolactose binds the repressor, causing it to dissociate from the operator.
Correct answer is: Allolactose
Q.101 During transcription initiation, what is the role of the σ factor in prokaryotes?
Helps RNA polymerase bind the promoter
Catalyzes phosphodiester bond formation
Adds the 5’ cap to mRNA
Releases the nascent RNA chain
Explanation - The σ factor directs RNA polymerase to the promoter region.
Correct answer is: Helps RNA polymerase bind the promoter
Q.102 Which of the following best describes the function of the 3’ end of mRNA during translation?
It contains the start codon
It is the site of tRNA binding
It contains the stop codon
It is the point of ribosome assembly
Explanation - The 3’ end of mRNA holds the stop codon where translation terminates.
Correct answer is: It contains the stop codon
Q.103 Which of the following best describes 'reverse transcription'?
DNA synthesis from an RNA template
RNA synthesis from a DNA template
Protein synthesis from RNA
DNA synthesis from a DNA template
Explanation - Reverse transcription converts RNA into DNA, as seen in retroviruses.
Correct answer is: DNA synthesis from an RNA template
Q.104 The 5' to 3' directionality in DNA replication refers to:
The direction the polymerase moves along the DNA strand
The orientation of the phosphodiester bond formation
The orientation of the sugar-phosphate backbone
Both B and C
Explanation - Polymerase adds nucleotides in the 5’→3’ direction, creating the backbone.
Correct answer is: Both B and C
Q.105 Which type of RNA is involved in splicing of pre-mRNA?
snRNA
tRNA
rRNA
mRNA
Explanation - snRNA is part of the spliceosome complex for intron removal.
Correct answer is: snRNA
Q.106 What is the role of the ribosomal exit tunnel?
Allows tRNA to enter the ribosome
Allows the nascent polypeptide to exit the ribosome
Binds the mRNA start codon
Binds the ribosomal P site tRNA
Explanation - The exit tunnel guides the emerging peptide chain out of the ribosome.
Correct answer is: Allows the nascent polypeptide to exit the ribosome
Q.107 Which of the following best describes the function of a promoter in gene expression?
Initiate DNA replication
Initiate transcription
Initiate translation
Initiate splicing
Explanation - Promoters are DNA sequences where RNA polymerase binds to start transcription.
Correct answer is: Initiate transcription
Q.108 In a typical eukaryotic gene, which of the following is NOT a feature?
Exons
Introns
Promoter
Polymerase II binding site
Explanation - While polymerase II binds the promoter, it is not a distinct feature separate from the promoter.
Correct answer is: Polymerase II binding site
Q.109 Which of the following is a characteristic of prokaryotic mRNA?
Contains introns
Has a 5’ cap
Is translated while being transcribed
Requires splicing before translation
Explanation - Prokaryotic transcription and translation can occur simultaneously.
Correct answer is: Is translated while being transcribed
Q.110 Which of the following is a common method for detecting mutations in a specific gene?
Northern blot
PCR followed by sequencing
Western blot
Southern blot
Explanation - PCR amplifies the region of interest, and sequencing identifies mutations.
Correct answer is: PCR followed by sequencing
Q.111 During DNA replication, which enzyme replaces RNA primers with DNA nucleotides?
DNA polymerase I
DNA polymerase III
RNA polymerase
Ligase
Explanation - DNA polymerase I has 5'→3' exonuclease activity to remove primers and replace them.
Correct answer is: DNA polymerase I
Q.112 Which of the following best describes the difference between a promoter and an operator in the lac operon?
Promoters are binding sites for RNA polymerase; operators are binding sites for repressor proteins
Promoters are binding sites for repressor proteins; operators are binding sites for RNA polymerase
Both are binding sites for RNA polymerase
Both are binding sites for repressor proteins
Explanation - Promoter initiates transcription; operator regulates it via repressor binding.
Correct answer is: Promoters are binding sites for RNA polymerase; operators are binding sites for repressor proteins
Q.113 Which enzyme is responsible for the addition of a poly-A tail to the 3’ end of mRNA?
Poly(A) polymerase
Poly(A) binding protein
RNA ligase
RNA polymerase II
Explanation - Poly(A) polymerase catalyzes the addition of adenine nucleotides.
Correct answer is: Poly(A) polymerase
Q.114 Which type of RNA is not involved in protein synthesis?
mRNA
tRNA
rRNA
snRNA
Explanation - snRNA is involved in splicing, not direct protein synthesis.
Correct answer is: snRNA
Q.115 Which of the following best describes the 'reading frame' in translation?
The number of bases in a codon
The set of three-nucleotide codons that the ribosome reads sequentially
The start codon position in the mRNA
The position of tRNA in the ribosome
Explanation - The reading frame is determined by how the ribosome groups nucleotides into codons.
Correct answer is: The set of three-nucleotide codons that the ribosome reads sequentially
Q.116 Which of the following best describes the role of the ribosomal large subunit?
Peptidyl transferase activity
mRNA binding
Initiation complex formation
Translocation of tRNA
Explanation - The large subunit contains the catalytic center for peptide bond formation.
Correct answer is: Peptidyl transferase activity
Q.117 Which of the following is a hallmark of a nonsense mutation?
A codon is changed to one that specifies a different amino acid
A codon is changed to a stop codon
A base is inserted or deleted causing a shift in reading frame
A base change does not alter the amino acid sequence
Explanation - A nonsense mutation creates a premature stop codon.
Correct answer is: A codon is changed to a stop codon
Q.118 In the genetic code, which of the following is a codon that specifies the amino acid serine?
UAA
UCU
AUG
UGA
Explanation - UCU, UCC, UCA, and UCG code for serine.
Correct answer is: UCU
Q.119 Which of the following best describes the role of the ribosomal small subunit?
Peptidyl transferase center
mRNA binding and initiation
Peptide chain exit
Translocation of tRNA
Explanation - The 40S small subunit recognizes the start codon and binds mRNA.
Correct answer is: mRNA binding and initiation
Q.120 Which enzyme catalyzes the formation of phosphodiester bonds during DNA synthesis?
DNA ligase
DNA polymerase
DNA helicase
DNA topoisomerase
Explanation - DNA polymerase adds nucleotides and forms phosphodiester bonds.
Correct answer is: DNA polymerase
Q.121 Which of the following best describes the function of the 3' untranslated region (UTR) of mRNA?
Regulates translation initiation
Encodes a signal peptide
Contains the stop codon
Regulates mRNA stability and localization
Explanation - The 3' UTR contains elements influencing degradation and transport.
Correct answer is: Regulates mRNA stability and localization
Q.122 In the context of CRISPR-Cas9, what does the PAM sequence refer to?
Protospacer adjacent motif
Protein associated motif
Primary active motif
Polymerase-associated motif
Explanation - PAM is a short DNA sequence required for Cas9 binding.
Correct answer is: Protospacer adjacent motif
Q.123 Which of the following is a typical function of a gene enhancer?
Inhibit transcription
Increase transcription of a gene
Promote mRNA degradation
Stop DNA replication
Explanation - Enhancers increase the efficiency of transcription initiation.
Correct answer is: Increase transcription of a gene
Q.124 Which enzyme is responsible for adding a 5’ cap to eukaryotic mRNA?
Capping enzyme
Poly(A) polymerase
RNA polymerase II
DNA ligase
Explanation - Capping enzymes transfer a methylated guanosine to the 5’ end of mRNA.
Correct answer is: Capping enzyme
Q.125 Which of the following best describes a point mutation?
A deletion of several nucleotides
An insertion of several nucleotides
A single base change
A chromosomal translocation
Explanation - A point mutation changes only one nucleotide in the sequence.
Correct answer is: A single base change
Q.126 What is the primary function of ribosomal protein L4 in prokaryotes?
Forms the exit tunnel for nascent polypeptide
Stabilizes the 30S subunit
Assists tRNA binding at the A site
Helps in peptide bond formation
Explanation - Ribosomal protein L4 lines the peptide exit tunnel of the large subunit.
Correct answer is: Forms the exit tunnel for nascent polypeptide