Q.1 What are the two types of nucleic acids found in cells?
DNA and RNA
DNA and proteins
RNA and lipids
Carbohydrates and DNA
Explanation - The two nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
Correct answer is: DNA and RNA
Q.2 Which of the following correctly describes the backbone of the DNA double helix?
Alternating sugar and phosphate groups
Alternating amino acids and sugars
Alternating phosphate and nitrogen bases
Alternating ribose and uracil
Explanation - DNA backbone is composed of deoxyribose sugars linked by phosphate groups.
Correct answer is: Alternating sugar and phosphate groups
Q.3 What base pairs with adenine in DNA?
Thymine
Cytosine
Guanine
Uracil
Explanation - In DNA, adenine (A) forms two hydrogen bonds with thymine (T).
Correct answer is: Thymine
Q.4 How many hydrogen bonds stabilize a G‑C base pair in DNA?
Three
Two
One
Four
Explanation - Guanine (G) pairs with cytosine (C) via three hydrogen bonds, making the pair stronger than A‑T.
Correct answer is: Three
Q.5 Which enzyme unwinds the DNA double helix during replication?
Helicase
Ligase
Polymerase
Topoisomerase
Explanation - Helicase separates the two strands of DNA by breaking hydrogen bonds.
Correct answer is: Helicase
Q.6 During DNA replication, which strand serves as the template for continuous synthesis?
Leading strand
Lagging strand
Both strands equally
Neither strand
Explanation - The leading strand is synthesized continuously in the direction of the replication fork.
Correct answer is: Leading strand
Q.7 Which of the following statements about DNA polymerase is FALSE?
It adds nucleotides only to the 3’ end of a growing strand.
It can synthesize DNA in the 5’→3’ direction.
It can add nucleotides to the 5’ end of a strand.
It requires a primer to start synthesis.
Explanation - DNA polymerase adds nucleotides only to the 3’ hydroxyl group; synthesis proceeds 5’→3’.
Correct answer is: It can add nucleotides to the 5’ end of a strand.
Q.8 What is the primary function of telomeres?
Protect chromosome ends from degradation
Initiate DNA replication
Code for essential proteins
Regulate gene expression
Explanation - Telomeres are repetitive sequences that safeguard chromosome termini during replication.
Correct answer is: Protect chromosome ends from degradation
Q.9 In which cellular organelle does DNA replication primarily occur in eukaryotes?
Nucleus
Mitochondria
Chloroplast
Ribosome
Explanation - Eukaryotic genomic DNA replicates inside the nucleus.
Correct answer is: Nucleus
Q.10 Which of the following is NOT a component of a nucleotide?
Phosphate group
Deoxyribose sugar
Amino acid
Nitrogenous base
Explanation - Nucleotides consist of a phosphate, a sugar (deoxyribose in DNA), and a nitrogenous base.
Correct answer is: Amino acid
Q.11 What is the shape of the DNA molecule as described by Watson and Crick?
Right‑handed double helix
Left‑handed double helix
Triple helix
Flat sheet
Explanation - DNA adopts a right‑handed double‑helical conformation.
Correct answer is: Right‑handed double helix
Q.12 Which base is found in RNA but not in DNA?
Uracil
Thymine
Cytosine
Guanine
Explanation - RNA replaces thymine with uracil as one of its four bases.
Correct answer is: Uracil
Q.13 What is the term for the complete set of genetic material in a cell?
Genome
Proteome
Transcriptome
Metabolome
Explanation - The genome encompasses all DNA sequences in an organism.
Correct answer is: Genome
Q.14 Which of the following best describes a gene?
A DNA segment that codes for a functional product
A protein that regulates cell division
A lipid that forms cell membranes
A carbohydrate that stores energy
Explanation - Genes are DNA sequences that are transcribed and often translated into proteins.
Correct answer is: A DNA segment that codes for a functional product
Q.15 In the semi‑conservative model of DNA replication, each new DNA molecule contains:
One original strand and one new strand
Two new strands
Two original strands
One original strand and one RNA strand
Explanation - Each daughter DNA retains one parental strand and synthesizes a complementary new strand.
Correct answer is: One original strand and one new strand
Q.16 Which of the following enzymes joins Okazaki fragments on the lagging strand?
DNA ligase
DNA helicase
RNA polymerase
Topoisomerase
Explanation - DNA ligase creates phosphodiester bonds to seal gaps between fragments.
Correct answer is: DNA ligase
Q.17 What is the role of a promoter in transcription?
It signals where RNA polymerase should bind to start transcription.
It terminates transcription.
It translates mRNA into protein.
It splices introns from pre‑mRNA.
Explanation - Promoters are DNA sequences upstream of a gene that recruit RNA polymerase.
Correct answer is: It signals where RNA polymerase should bind to start transcription.
Q.18 Which of the following statements about introns is correct?
Introns are non‑coding regions removed from pre‑mRNA.
Introns code for essential proteins.
Introns are only present in prokaryotic genes.
Introns are the same as exons.
Explanation - During RNA processing, introns are spliced out, leaving exons to form mature mRNA.
Correct answer is: Introns are non‑coding regions removed from pre‑mRNA.
Q.19 What is the function of DNA topoisomerase during replication?
Relieves supercoiling ahead of the replication fork.
Synthesizes new DNA strands.
Adds nucleotides to the 5' end.
Separates the two DNA strands.
Explanation - Topoisomerases cut and re‑join DNA to manage torsional strain.
Correct answer is: Relieves supercoiling ahead of the replication fork.
Q.20 Which type of mutation results in a premature stop codon?
Nonsense mutation
Missense mutation
Silent mutation
Frameshift mutation
Explanation - A nonsense mutation converts a codon for an amino acid into a stop codon, truncating translation.
Correct answer is: Nonsense mutation
Q.21 In which of the following processes is DNA used as a template to produce RNA?
Transcription
Translation
Replication
Splicing
Explanation - Transcription synthesizes RNA using one DNA strand as a template.
Correct answer is: Transcription
Q.22 Which of the following is a characteristic of a point mutation?
Alteration of a single nucleotide base
Insertion of a large DNA segment
Deletion of an entire chromosome
Duplication of a gene
Explanation - Point mutations involve changes at a single nucleotide position.
Correct answer is: Alteration of a single nucleotide base
Q.23 What is the significance of the antiparallel orientation of DNA strands?
It allows complementary base pairing between opposite strands.
It creates a double‑helix with a left‑handed twist.
It enables DNA to bind to ribosomes directly.
It permits both strands to be transcribed simultaneously.
Explanation - Antiparallel strands (5'→3' opposite 3'←5') enable hydrogen bonding between complementary bases.
Correct answer is: It allows complementary base pairing between opposite strands.
Q.24 Which technique separates DNA fragments based on size?
Gel electrophoresis
PCR
Western blot
Chromatography
Explanation - DNA fragments migrate through agarose gel; smaller fragments travel faster.
Correct answer is: Gel electrophoresis
Q.25 What does the acronym PCR stand for?
Polymerase Chain Reaction
Protein Coding Region
Partial Codon Replication
Phosphodiester Chain Rearrangement
Explanation - PCR amplifies specific DNA sequences using repeated cycles of denaturation, annealing, and extension.
Correct answer is: Polymerase Chain Reaction
Q.26 During DNA replication, what provides the starting point for DNA synthesis?
RNA primer
DNA ligase
DNA topoisomerase
Helicase
Explanation - Primase synthesizes a short RNA primer that DNA polymerase extends.
Correct answer is: RNA primer
Q.27 Which of the following best describes a frameshift mutation?
Insertion or deletion of nucleotides that alters the reading frame
Change of a single base that creates a stop codon
Substitution of one base that does not change the amino acid
Duplication of an entire chromosome
Explanation - Frameshift mutations shift the codon grouping, usually leading to a nonfunctional protein.
Correct answer is: Insertion or deletion of nucleotides that alters the reading frame
Q.28 What is the role of histones in eukaryotic DNA organization?
They package DNA into nucleosomes, forming chromatin.
They synthesize RNA from DNA templates.
They act as enzymes that cut DNA strands.
They transport DNA out of the nucleus.
Explanation - Histone proteins wrap DNA, facilitating compaction and regulation.
Correct answer is: They package DNA into nucleosomes, forming chromatin.
Q.29 Which of the following is the correct order of steps in the central dogma of molecular biology?
DNA → RNA → Protein
RNA → DNA → Protein
Protein → DNA → RNA
DNA → Protein → RNA
Explanation - Genetic information flows from DNA to RNA (transcription) and then to protein (translation).
Correct answer is: DNA → RNA → Protein
Q.30 What is the function of a ribosome?
Catalyze protein synthesis by translating mRNA.
Replicate DNA during cell division.
Transcribe DNA into RNA.
Modify lipids for membrane synthesis.
Explanation - Ribosomes read mRNA codons and join amino acids into a polypeptide chain.
Correct answer is: Catalyze protein synthesis by translating mRNA.
Q.31 Which DNA modification is most commonly associated with gene silencing in eukaryotes?
Methylation of cytosine bases
Phosphorylation of adenine bases
Acetylation of thymine bases
Ubiquitination of guanine bases
Explanation - 5‑methylcytosine in promoter regions often reduces transcriptional activity.
Correct answer is: Methylation of cytosine bases
Q.32 In which phase of the cell cycle does DNA replication occur?
S phase
G1 phase
M phase
G2 phase
Explanation - Synthesis (S) phase is dedicated to duplicating the genome.
Correct answer is: S phase
Q.33 What does the term ‘genetic code’ refer to?
The set of rules by which nucleotide triplets specify amino acids.
The sequence of DNA that codes for ribosomal RNA.
The arrangement of histones on DNA.
The pattern of DNA methylation across the genome.
Explanation - The genetic code translates three‑base codons into specific amino acids during translation.
Correct answer is: The set of rules by which nucleotide triplets specify amino acids.
Q.34 How many codons are possible in the standard genetic code?
64
20
4
61
Explanation - Four bases in groups of three give 4³ = 64 possible codons; three are stop codons, leaving 61 for amino acids.
Correct answer is: 64
Q.35 Which of the following statements about plasmids is true?
They are circular DNA molecules that can replicate independently of chromosomal DNA.
They are linear fragments of RNA found only in mitochondria.
They encode the majority of essential genes in eukaryotes.
They are protein complexes that bind DNA.
Explanation - Plasmids are extrachromosomal DNA often used in molecular cloning.
Correct answer is: They are circular DNA molecules that can replicate independently of chromosomal DNA.
Q.36 What is the main purpose of the DNA sequencing method known as Sanger sequencing?
To determine the exact order of nucleotides in a DNA fragment.
To amplify DNA exponentially.
To separate DNA fragments by size.
To edit specific genes in living cells.
Explanation - Sanger sequencing uses chain‑terminating dideoxynucleotides to read DNA sequences.
Correct answer is: To determine the exact order of nucleotides in a DNA fragment.
Q.37 In DNA, which sugar is present in the backbone?
Deoxyribose
Ribose
Glucose
Fructose
Explanation - DNA contains deoxyribose, lacking a hydroxyl group at the 2’ carbon.
Correct answer is: Deoxyribose
Q.38 Which of the following best describes a silent mutation?
A nucleotide change that does not alter the encoded amino acid.
A mutation that introduces a premature stop codon.
An insertion that shifts the reading frame.
A deletion that removes an entire gene.
Explanation - Because of codon degeneracy, some base changes still code for the same amino acid.
Correct answer is: A nucleotide change that does not alter the encoded amino acid.
Q.39 What type of bond holds the two strands of DNA together?
Hydrogen bonds between complementary bases
Covalent phosphodiester bonds
Ionic bonds between phosphate groups
Disulfide bonds between nucleotides
Explanation - Base pairing via hydrogen bonds stabilizes the double helix.
Correct answer is: Hydrogen bonds between complementary bases
Q.40 What is the role of the 5’ cap added to eukaryotic mRNA?
Protects mRNA from degradation and aids ribosome binding.
Signals termination of transcription.
Facilitates splicing of introns.
Directs mRNA to the mitochondria.
Explanation - The 7‑methylguanosine cap enhances stability and translation initiation.
Correct answer is: Protects mRNA from degradation and aids ribosome binding.
Q.41 Which of the following is a characteristic of a prokaryotic genome?
DNA is organized in a single circular chromosome.
DNA is packaged into nucleosomes.
Genes contain introns.
DNA replication occurs in the nucleus.
Explanation - Prokaryotes typically have a circular chromosome and lack a defined nucleus.
Correct answer is: DNA is organized in a single circular chromosome.
Q.42 During translation, what is the function of tRNA?
To deliver specific amino acids to the ribosome according to codon‑anticodon pairing.
To unwind mRNA secondary structures.
To catalyze peptide bond formation.
To splice introns from pre‑mRNA.
Explanation - Transfer RNA matches its anticodon with mRNA codons and carries the corresponding amino acid.
Correct answer is: To deliver specific amino acids to the ribosome according to codon‑anticodon pairing.
Q.43 What does a ‘mutation hotspot’ refer to?
A region of the genome with a high frequency of mutations.
A DNA segment that cannot be mutated.
A protein that repairs DNA damage.
A site where DNA replication always starts.
Explanation - Hotspots are prone to changes due to sequence context or environmental factors.
Correct answer is: A region of the genome with a high frequency of mutations.
Q.44 Which laboratory technique uses a fluorescent probe to detect specific DNA sequences?
Fluorescence in situ hybridization (FISH)
Southern blot
Northern blot
ELISA
Explanation - FISH hybridizes labeled probes to chromosomes, visualizing target DNA under a fluorescence microscope.
Correct answer is: Fluorescence in situ hybridization (FISH)
Q.45 Which of the following best describes the function of a promoter’s TATA box?
It helps position RNA polymerase II for transcription initiation.
It signals the end of transcription.
It encodes the start codon for translation.
It binds ribosomal proteins.
Explanation - The TATA box is a conserved DNA element that aids assembly of the transcription initiation complex.
Correct answer is: It helps position RNA polymerase II for transcription initiation.
Q.46 What is the significance of the ‘reading frame’ in protein coding DNA?
It determines how nucleotides are grouped into codons for translation.
It indicates the direction of DNA replication.
It shows where DNA is methylated.
It specifies the location of introns.
Explanation - A correct reading frame groups bases in sets of three; shifting it changes downstream amino acids.
Correct answer is: It determines how nucleotides are grouped into codons for translation.
Q.47 Which of the following enzymes is essential for removing RNA primers during DNA replication in eukaryotes?
DNA polymerase δ
RNase H
DNA ligase I
Helicase
Explanation - RNase H degrades the RNA portion of RNA‑DNA hybrids, allowing replacement with DNA.
Correct answer is: RNase H
Q.48 What does the term ‘epigenetics’ refer to?
Heritable changes in gene expression without changes in DNA sequence.
Mutations that alter the coding sequence of a gene.
The study of protein structures.
The process of DNA replication.
Explanation - Epigenetic mechanisms include DNA methylation and histone modifications.
Correct answer is: Heritable changes in gene expression without changes in DNA sequence.
Q.49 In the context of DNA, what does the term ‘GC‑rich region’ imply about its properties?
It has higher thermal stability due to three hydrogen bonds per G‑C pair.
It is more prone to single‑strand breaks.
It contains more uracil than thymine.
It is always located at the start of a gene.
Explanation - G‑C pairs form three hydrogen bonds, raising the melting temperature of GC‑rich DNA.
Correct answer is: It has higher thermal stability due to three hydrogen bonds per G‑C pair.
Q.50 Which of the following best explains why DNA polymerases have a proofreading function?
To remove incorrectly incorporated nucleotides via 3’→5’ exonuclease activity.
To add extra nucleotides at the end of the strand.
To unwind the DNA double helix.
To attach histones to newly synthesized DNA.
Explanation - Proofreading improves fidelity by excising mismatched bases during replication.
Correct answer is: To remove incorrectly incorporated nucleotides via 3’→5’ exonuclease activity.
Q.51 Which of the following statements about mitochondrial DNA (mtDNA) is correct?
It is circular and inherited maternally.
It is linear and inherited from both parents.
It contains introns like nuclear DNA.
It encodes ribosomal RNA only.
Explanation - Human mtDNA is a small circular genome transmitted through the egg.
Correct answer is: It is circular and inherited maternally.
Q.52 What is the purpose of the poly‑A tail added to eukaryotic mRNA?
To enhance mRNA stability and aid export from the nucleus.
To signal the start of translation.
To act as a ribosome binding site.
To splice introns from pre‑mRNA.
Explanation - The poly‑adenine tail protects mRNA from degradation and assists nuclear export.
Correct answer is: To enhance mRNA stability and aid export from the nucleus.
Q.53 During which process are introns removed from a primary RNA transcript?
RNA splicing
Translation
DNA replication
Transcription
Explanation - The spliceosome excises introns, joining exons to create mature mRNA.
Correct answer is: RNA splicing
Q.54 Which of the following best describes the term ‘codon bias’?
Preference for certain synonymous codons over others in a genome.
The use of rare codons to regulate gene expression.
A mutation that changes one codon to another.
The inability of a codon to bind any tRNA.
Explanation - Codon bias reflects differential usage of synonymous codons, affecting translation efficiency.
Correct answer is: Preference for certain synonymous codons over others in a genome.
Q.55 Which molecular technique allows for the quantification of specific DNA sequences in real‑time?
Quantitative PCR (qPCR)
Southern blot
DNA microarray
Sanger sequencing
Explanation - qPCR monitors fluorescence during amplification to measure DNA quantity.
Correct answer is: Quantitative PCR (qPCR)
Q.56 What is the main difference between DNA and RNA regarding the sugar component?
DNA contains deoxyribose; RNA contains ribose.
DNA contains ribose; RNA contains deoxyribose.
Both contain deoxyribose.
Both contain ribose.
Explanation - The 2’ hydroxyl group distinguishes ribose (RNA) from deoxyribose (DNA).
Correct answer is: DNA contains deoxyribose; RNA contains ribose.
Q.57 Which of the following enzymes catalyzes the formation of phosphodiester bonds during DNA synthesis?
DNA polymerase
RNA polymerase
Helicase
Ligase
Explanation - DNA polymerase adds nucleotides to the 3’ end, forming phosphodiester linkages.
Correct answer is: DNA polymerase
Q.58 What is the effect of a missense mutation?
It changes one amino acid in the protein product.
It creates a stop codon.
It does not alter the amino acid sequence.
It shifts the reading frame.
Explanation - A missense mutation substitutes a codon for a different amino acid.
Correct answer is: It changes one amino acid in the protein product.
Q.59 Which of the following best explains why DNA is a stable molecule for genetic storage?
It has a double‑helix structure with internal base pairing and a deoxyribose backbone.
It is single‑stranded and flexible.
It contains ribose, which is more reactive.
It is composed mainly of proteins.
Explanation - The double helix protects bases and the deoxyribose lacks a 2’ OH, reducing hydrolysis.
Correct answer is: It has a double‑helix structure with internal base pairing and a deoxyribose backbone.
Q.60 Which process generates a complementary DNA (cDNA) copy from an RNA template?
Reverse transcription
Transcription
Replication
Translation
Explanation - Reverse transcriptase synthesizes DNA using RNA as a template, common in retroviruses.
Correct answer is: Reverse transcription
Q.61 During DNA replication, the term ‘origin of replication’ refers to:
Specific DNA sequences where replication begins.
The site where transcription ends.
The region coding for ribosomal RNA.
A protein that binds to DNA.
Explanation - Origins are recognized by initiator proteins to start fork formation.
Correct answer is: Specific DNA sequences where replication begins.
Q.62 What is the role of the sigma (σ) factor in bacterial transcription?
It directs RNA polymerase to specific promoter regions.
It terminates transcription.
It splices introns from mRNA.
It adds a 5’ cap to mRNA.
Explanation - The σ factor binds promoter elements and facilitates polymerase initiation.
Correct answer is: It directs RNA polymerase to specific promoter regions.
Q.63 Which of the following best describes an operon?
A cluster of co‑regulated genes under a single promoter in prokaryotes.
A eukaryotic DNA segment that codes for multiple proteins.
A protein complex that replicates DNA.
A type of RNA polymerase.
Explanation - Operons allow coordinated expression of functionally related genes.
Correct answer is: A cluster of co‑regulated genes under a single promoter in prokaryotes.
Q.64 Which method is commonly used to amplify a specific DNA fragment exponentially?
Polymerase Chain Reaction (PCR)
Southern blotting
DNA sequencing
Northern blotting
Explanation - PCR uses cycles of denaturation, annealing, and extension to amplify DNA.
Correct answer is: Polymerase Chain Reaction (PCR)
Q.65 What is the functional significance of the ‘A‑form’ DNA helix compared to the common ‘B‑form’?
A‑form is shorter and wider, occurring in dehydrated conditions or RNA‑DNA hybrids.
A‑form is longer and thinner, present in all living cells.
A‑form contains thymine instead of uracil.
A‑form lacks hydrogen bonding between bases.
Explanation - A‑form DNA appears under low‑humidity or when DNA is RNA‑paired; it has 11 bp per turn.
Correct answer is: A‑form is shorter and wider, occurring in dehydrated conditions or RNA‑DNA hybrids.
Q.66 Which of the following best explains why DNA replication is considered ‘semi‑conservative’?
Each daughter molecule contains one parental and one newly synthesized strand.
Both strands of the parent are completely conserved in each daughter.
Only half of the genetic information is passed to each daughter cell.
The replication process conserves only the sequence of adenine.
Explanation - The semi‑conservative model, proven by Meselson‑Stahl, describes this strand distribution.
Correct answer is: Each daughter molecule contains one parental and one newly synthesized strand.
Q.67 In eukaryotes, which of the following is the primary site of transcription?
Nucleus
Cytoplasm
Mitochondria
Ribosome
Explanation - Transcription of nuclear DNA occurs within the nucleus before mRNA export.
Correct answer is: Nucleus
Q.68 What is the effect of a ‘CpG island’ in a gene promoter region?
Often associated with active transcription when unmethylated.
Always silences the gene regardless of methylation status.
Prevents binding of transcription factors.
Causes immediate degradation of mRNA.
Explanation - CpG islands are CG‑rich regions; lack of methylation correlates with gene expression.
Correct answer is: Often associated with active transcription when unmethylated.
Q.69 Which of the following correctly pairs a DNA polymerase with its primary function in eukaryotes?
DNA polymerase δ – synthesis of the lagging strand.
DNA polymerase α – proofreading activity.
DNA polymerase ε – removal of RNA primers.
DNA polymerase γ – replication of nuclear DNA.
Explanation - Pol δ primarily extends Okazaki fragments; Pol ε synthesizes the leading strand.
Correct answer is: DNA polymerase δ – synthesis of the lagging strand.
Q.70 Which of the following processes is directly responsible for generating genetic diversity during meiosis?
Crossing over (homologous recombination).
DNA replication.
RNA splicing.
Translation.
Explanation - Recombination exchanges DNA segments between homologous chromosomes, creating new allele combinations.
Correct answer is: Crossing over (homologous recombination).
Q.71 What is the main reason why RNA is more chemically unstable than DNA?
RNA contains a 2’ hydroxyl group that makes the backbone prone to hydrolysis.
RNA is single‑stranded.
RNA lacks a phosphate backbone.
RNA has thymine instead of uracil.
Explanation - The 2’ OH can act as a nucleophile, cleaving the phosphodiester bond.
Correct answer is: RNA contains a 2’ hydroxyl group that makes the backbone prone to hydrolysis.
Q.72 In a DNA sequencing gel, why do smaller fragments travel farther than larger ones?
They encounter less resistance moving through the pores of the gel.
They have a higher negative charge per base.
They are more hydrophobic.
They bind more tightly to the gel matrix.
Explanation - Gel electrophoresis separates DNA by size; smaller fragments migrate faster.
Correct answer is: They encounter less resistance moving through the pores of the gel.
Q.73 Which of the following best describes the term ‘genome-wide association study (GWAS)’?
A study that scans many genomes to find genetic variants associated with a trait.
A technique to edit specific genes.
An analysis of protein expression patterns.
A method to visualize chromosomes under a microscope.
Explanation - GWAS identifies SNPs correlated with diseases or phenotypes across populations.
Correct answer is: A study that scans many genomes to find genetic variants associated with a trait.
Q.74 What is the primary structural difference between a plasmid and a chromosome?
Plasmids are usually circular and extrachromosomal; chromosomes are linear and part of the main genome.
Plasmids contain only RNA, while chromosomes contain DNA.
Plasmids are always larger than chromosomes.
Plasmids are composed of proteins.
Explanation - Plasmids can replicate independently and often carry accessory genes.
Correct answer is: Plasmids are usually circular and extrachromosomal; chromosomes are linear and part of the main genome.
Q.75 Which of the following is the correct description of a ‘codon’?
A sequence of three nucleotides that codes for one amino acid.
A pair of nucleotides that holds the DNA strands together.
A stretch of DNA that signals termination of transcription.
A region where DNA is methylated.
Explanation - Triplet codons are read by ribosomes during translation.
Correct answer is: A sequence of three nucleotides that codes for one amino acid.
Q.76 What does the term ‘non‑coding RNA’ refer to?
RNA molecules that are not translated into proteins but have regulatory or structural roles.
RNA that is degraded immediately after transcription.
RNA that is only found in viruses.
RNA that contains only uracil.
Explanation - Examples include rRNA, tRNA, miRNA, and lncRNA.
Correct answer is: RNA molecules that are not translated into proteins but have regulatory or structural roles.
Q.77 Which of the following enzymes is responsible for adding the poly‑A tail to eukaryotic mRNA?
Poly(A) polymerase
RNA polymerase II
DNA ligase
Helicase
Explanation - Poly(A) polymerase catalyzes the addition of adenine nucleotides to the 3’ end of pre‑mRNA.
Correct answer is: Poly(A) polymerase
Q.78 In the context of DNA repair, what does the term ‘nucleotide excision repair (NER)’ describe?
Removal of a short single‑stranded DNA segment containing a lesion, followed by DNA synthesis.
Direct reversal of thymine dimers without cutting DNA.
Repair of double‑strand breaks by homologous recombination.
Methylation of damaged bases to silence them.
Explanation - NER excises bulky DNA lesions such as UV‑induced pyrimidine dimers.
Correct answer is: Removal of a short single‑stranded DNA segment containing a lesion, followed by DNA synthesis.
Q.79 Which of the following best explains why DNA polymerases cannot initiate synthesis de novo?
They require a free 3’‑OH group provided by a primer.
They need a double‑stranded template.
They require ATP hydrolysis for each nucleotide added.
They need a ribosome to function.
Explanation - DNA polymerases add nucleotides to an existing 3’ hydroxyl group; primase provides the primer.
Correct answer is: They require a free 3’‑OH group provided by a primer.
Q.80 What is the main purpose of the CRISPR‑Cas9 system in molecular biology?
Targeted genome editing by creating double‑strand breaks at specific loci.
Amplifying DNA fragments.
Sequencing DNA strands.
Measuring gene expression levels.
Explanation - Cas9, guided by RNA, introduces cuts enabling insertion, deletion, or modification of DNA.
Correct answer is: Targeted genome editing by creating double‑strand breaks at specific loci.
Q.81 Which of the following statements about the ‘central dogma’ is FALSE?
RNA can be reverse transcribed into DNA.
DNA is directly translated into protein.
Information flow generally follows DNA → RNA → Protein.
Some RNAs have catalytic activity (ribozymes).
Explanation - Translation uses mRNA as an intermediate; DNA must first be transcribed.
Correct answer is: DNA is directly translated into protein.
Q.82 Which of the following best describes a ‘pseudogene’?
A DNA sequence resembling a functional gene but lacking coding potential.
A gene that is highly expressed.
A gene that codes for a protein involved in photosynthesis.
A gene that is only found in prokaryotes.
Explanation - Pseudogenes arise from duplication or retrotransposition and are usually nonfunctional.
Correct answer is: A DNA sequence resembling a functional gene but lacking coding potential.
Q.83 What is the primary reason that G‑C rich regions have a higher melting temperature (Tm) than A‑T rich regions?
G‑C base pairs form three hydrogen bonds, compared with two for A‑T.
G‑C pairs are larger in size.
A‑T pairs are located on the outer helix.
G‑C regions have more phosphate groups.
Explanation - Additional hydrogen bonds increase thermal stability, raising the Tm.
Correct answer is: G‑C base pairs form three hydrogen bonds, compared with two for A‑T.
Q.84 Which of the following best defines a ‘gene promoter’?
A DNA segment upstream of a gene that facilitates binding of RNA polymerase.
A protein that binds to DNA to repress transcription.
A region that codes for the start codon.
A segment that terminates transcription.
Explanation - Promoters contain regulatory elements such as TATA boxes and transcription factor binding sites.
Correct answer is: A DNA segment upstream of a gene that facilitates binding of RNA polymerase.
Q.85 Which of the following is NOT a typical post‑translational modification of proteins?
Phosphorylation
Methylation
Glycosylation
Transcription
Explanation - Transcription is the synthesis of RNA from DNA, not a protein modification.
Correct answer is: Transcription
Q.86 During DNA replication, what is the function of the sliding clamp (PCNA in eukaryotes)?
It holds DNA polymerase onto the template, increasing processivity.
It unwinds the DNA double helix.
It adds nucleotides to the growing strand.
It removes RNA primers.
Explanation - PCNA forms a ring around DNA, preventing polymerase dissociation.
Correct answer is: It holds DNA polymerase onto the template, increasing processivity.
Q.87 Which of the following best describes the term ‘genetic linkage’?
The tendency of alleles that are close together on a chromosome to be inherited together.
The random assortment of chromosomes during meiosis.
The process by which DNA is transcribed into RNA.
The mutation rate of a gene.
Explanation - Linked genes are less likely to be separated by recombination.
Correct answer is: The tendency of alleles that are close together on a chromosome to be inherited together.
Q.88 What is the main purpose of using a ‘vector’ in molecular cloning?
To carry and replicate foreign DNA within a host cell.
To cut DNA at specific sites.
To label DNA with fluorescent dyes.
To sequence DNA directly.
Explanation - Vectors (e.g., plasmids) enable insertion, replication, and expression of cloned DNA.
Correct answer is: To carry and replicate foreign DNA within a host cell.
Q.89 Which of the following best explains why DNA is considered a ‘template’ during transcription?
It provides the sequence of bases that determine the RNA sequence.
It is translated directly into protein.
It is degraded after transcription.
It forms the ribosome.
Explanation - RNA polymerase reads the DNA template strand to synthesize complementary RNA.
Correct answer is: It provides the sequence of bases that determine the RNA sequence.
Q.90 In a double‑stranded DNA molecule, which strand is referred to as the ‘sense’ strand?
The strand that has the same sequence as the mRNA (except T→U).
The strand that serves as the template for transcription.
The strand that contains introns.
The strand that is always methylated.
Explanation - The sense (coding) strand matches the mRNA transcript; the antisense strand is the template.
Correct answer is: The strand that has the same sequence as the mRNA (except T→U).
Q.91 Which of the following is an example of a ‘housekeeping gene’?
GAPDH
TP53
MYC
BRCA1
Explanation - Housekeeping genes are constitutively expressed to maintain basic cellular functions; GAPDH is commonly used as a control.
Correct answer is: GAPDH
Q.92 Which type of RNA carries amino acids to the ribosome during translation?
Transfer RNA (tRNA)
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
MicroRNA (miRNA)
Explanation - tRNA molecules have anticodons that pair with mRNA codons and deliver the appropriate amino acid.
Correct answer is: Transfer RNA (tRNA)
Q.93 Which of the following best describes the phenomenon of ‘alternative splicing’?
A single gene can produce multiple mRNA variants by including or excluding exons.
Introns are removed and never reinserted.
DNA is replicated in a different direction.
RNA polymerase transcribes only one exon at a time.
Explanation - Alternative splicing increases proteomic diversity from a limited number of genes.
Correct answer is: A single gene can produce multiple mRNA variants by including or excluding exons.
Q.94 Which of the following is the most common method for detecting single‑nucleotide polymorphisms (SNPs)?
Allele‑specific PCR
Southern blotting
Western blotting
DNA sequencing by synthesis
Explanation - Allele‑specific PCR uses primers that match the SNP allele, allowing selective amplification.
Correct answer is: Allele‑specific PCR
Q.95 What is the main role of the ‘RNA polymerase II’ enzyme in eukaryotes?
Synthesizing mRNA from DNA templates.
Synthesizing tRNA molecules.
Replicating DNA during S phase.
Splicing introns from pre‑mRNA.
Explanation - RNA Pol II transcribes protein‑coding genes into primary mRNA transcripts.
Correct answer is: Synthesizing mRNA from DNA templates.
Q.96 Which of the following best explains why DNA replication is bidirectional?
Two replication forks move away from each origin of replication.
DNA polymerase can synthesize in both directions simultaneously.
Helicase unwinds DNA on both sides of the fork.
RNA primers are synthesized on both strands.
Explanation - Each origin creates two forks that replicate DNA in opposite directions.
Correct answer is: Two replication forks move away from each origin of replication.
Q.97 In the context of DNA sequencing, what does the term ‘coverage depth’ refer to?
The average number of times each base is read during sequencing.
The length of the DNA fragment sequenced.
The number of chromosomes in a cell.
The speed at which nucleotides are added.
Explanation - Higher coverage increases confidence in the accuracy of the sequence data.
Correct answer is: The average number of times each base is read during sequencing.
Q.98 Which of the following best describes a ‘riboswitch’?
An RNA element that changes conformation upon binding a metabolite, regulating gene expression.
A DNA segment that encodes ribosomal proteins.
A protein that binds to ribosomal RNA.
A type of tRNA that carries multiple amino acids.
Explanation - Riboswitches are cis‑regulatory RNAs that control transcription or translation in response to ligands.
Correct answer is: An RNA element that changes conformation upon binding a metabolite, regulating gene expression.
Q.99 Which of the following statements about the ‘central dogma’ is most accurate in modern biology?
Information flow can be bidirectional, e.g., reverse transcription.
DNA is directly translated into protein without RNA.
RNA never serves as a template for DNA synthesis.
Proteins can be transcribed into RNA.
Explanation - Retroviruses and cellular processes like telomere maintenance use reverse transcription, extending the original dogma.
Correct answer is: Information flow can be bidirectional, e.g., reverse transcription.
Q.100 Which of the following is the most likely consequence of a mutation that creates a premature stop codon early in a coding sequence?
Production of a truncated, likely nonfunctional protein.
Increased stability of the protein.
No effect on the protein because of redundancy.
Conversion of the gene into a regulatory RNA.
Explanation - Premature stop codons lead to early termination of translation, often resulting in loss of function.
Correct answer is: Production of a truncated, likely nonfunctional protein.
Q.101 What is the primary purpose of using a ‘restriction enzyme’ in recombinant DNA technology?
To cut DNA at specific sequences, generating compatible ends for ligation.
To amplify DNA fragments.
To label DNA with fluorescent tags.
To transcribe DNA into RNA.
Explanation - Restriction endonucleases recognize palindromic sites and produce sticky or blunt ends for cloning.
Correct answer is: To cut DNA at specific sequences, generating compatible ends for ligation.
Q.102 Which of the following best describes the term ‘genomic imprinting’?
Parent‑of‑origin specific expression of certain genes, often via DNA methylation.
Random activation of one allele of a gene.
Duplication of an entire chromosome.
Insertion of viral DNA into the genome.
Explanation - Imprinted genes are expressed preferentially from either the maternal or paternal allele.
Correct answer is: Parent‑of‑origin specific expression of certain genes, often via DNA methylation.
Q.103 Which of the following accurately describes the role of a ‘chaperone protein’?
Assists in proper protein folding and prevents aggregation.
Catalyzes the formation of phosphodiester bonds in DNA.
Acts as a transcription factor.
Serves as a template for DNA replication.
Explanation - Molecular chaperones help nascent polypeptides attain correct conformation.
Correct answer is: Assists in proper protein folding and prevents aggregation.
Q.104 Which of the following is a hallmark of eukaryotic transcription termination for most RNA polymerase II transcripts?
Cleavage of the pre‑mRNA followed by polyadenylation.
Addition of a 5’ cap.
Formation of a hairpin loop in the RNA.
Binding of a terminator protein at the DNA.
Explanation - RNA Pol II transcripts are cleaved downstream of a poly‑A signal and then polyadenylated.
Correct answer is: Cleavage of the pre‑mRNA followed by polyadenylation.
Q.105 Which of the following best explains why mitochondria contain their own DNA?
They originated from an ancestral endosymbiotic bacterium.
They need to store extra genetic information for the cell.
Mitochondrial DNA encodes ribosomal proteins only.
Mitochondria replicate independently of the cell cycle.
Explanation - The endosymbiotic theory posits that mitochondria retain a small genome from their bacterial ancestor.
Correct answer is: They originated from an ancestral endosymbiotic bacterium.
Q.106 Which of the following best describes the function of a ‘transcription factor’?
A protein that binds specific DNA sequences to regulate transcription.
An enzyme that synthesizes RNA.
A molecule that degrades mRNA.
A lipid that anchors DNA to the membrane.
Explanation - Transcription factors can activate or repress gene expression by interacting with promoter/enhancer elements.
Correct answer is: A protein that binds specific DNA sequences to regulate transcription.
Q.107 In the context of DNA replication, what does the term ‘replisome’ refer to?
The multiprotein complex that carries out DNA synthesis at a replication fork.
A region of DNA that is highly methylated.
A type of RNA that regulates replication.
A DNA sequence that signals termination.
Explanation - The replisome includes helicase, polymerases, sliding clamps, and other factors.
Correct answer is: The multiprotein complex that carries out DNA synthesis at a replication fork.
Q.108 Which of the following best characterizes a ‘non‑canonical base pair’ in DNA?
A pairing that deviates from the standard A‑T and G‑C rules.
A pair that forms three hydrogen bonds.
A pair that occurs only in RNA.
A pair that is always lethal.
Explanation - Non‑canonical pairs like G‑T or A‑C can occur under certain conditions, affecting structure and mutagenesis.
Correct answer is: A pairing that deviates from the standard A‑T and G‑C rules.
Q.109 What is the primary advantage of using next‑generation sequencing (NGS) over Sanger sequencing?
Massively parallel processing allows sequencing of millions of fragments simultaneously.
NGS reads are longer than Sanger reads.
NGS does not require DNA amplification.
NGS can only sequence RNA.
Explanation - NGS provides high throughput, reducing time and cost per base compared to Sanger sequencing.
Correct answer is: Massively parallel processing allows sequencing of millions of fragments simultaneously.
Q.110 Which of the following best explains why DNA is negatively charged?
The phosphate groups in the backbone carry negative charges.
The nitrogenous bases are negatively charged.
DNA binds positively charged proteins.
DNA contains abundant acidic amino acids.
Explanation - Each phosphate group has a negatively charged oxygen, giving DNA an overall negative charge.
Correct answer is: The phosphate groups in the backbone carry negative charges.