Molecular Biology MCQs
Molecular Biology MCQs with Answers and Explanations
These MCQs are important for CBSE/State Boards, NEET-UG/PG, Medical Science Entrances, and Competitive Exams worldwide.
Q1. The sugar present in DNA is:
A. Ribose
Explanation: Incorrect. Ribose has a 2′-OH and occurs in RNA, not DNA.
B. Deoxyribose
Answer: Correct. DNA contains deoxyribose lacking a 2′-hydroxyl group.
C. Fructose
Explanation: Incorrect. Fructose is not a component of nucleic acids.
D. Glucose
Explanation: Incorrect. Glucose is a hexose used in energy metabolism, not nucleic acids.
Q2. Chargaff’s rule states that in double-stranded DNA:
A. A = G and C = T
Explanation: Incorrect. Purines do not equal each other universally.
B. A = T and G = C
Answer: Correct. Complementary base pairing makes A equal T and G equal C.
C. A + T = G + C in all species
Explanation: Incorrect. A+T and G+C vary among species.
D. A/T ratio is constant across species
Explanation: Incorrect. The A/T ratio varies by organism; only A=T holds within a molecule.
Q3. The bond between base pairs in DNA is primarily:
A. Phosphodiester bond
Explanation: Incorrect. Phosphodiester bonds link nucleotides along a strand, not between bases.
B. Glycosidic bond
Explanation: Incorrect. Glycosidic bonds join base to sugar.
C. Hydrogen bond
Answer: Correct. Hydrogen bonds mediate A–T (2) and G–C (3) pairing.
D. Ionic bond
Explanation: Incorrect. Ionic interactions are not the main force for specific base pairing.
Q4. Which enzyme unwinds the DNA helix ahead of the replication fork?
A. DNA polymerase III
Explanation: Incorrect. DNA polymerase III synthesizes DNA, it does not unwind the helix.
B. Helicase
Answer: Correct. Helicase breaks hydrogen bonds to separate strands.
C. Ligase
Explanation: Incorrect. Ligase seals nicks in the sugar–phosphate backbone.
D. Topoisomerase I
Explanation: Incorrect. Topoisomerase relieves supercoiling; it does not separate base pairs.
Q5. Okazaki fragments are formed:
A. On the leading strand only
Explanation: Incorrect. Leading strand is synthesized continuously.
B. On both strands
Explanation: Incorrect. Only the lagging strand is discontinuous.
C. On the lagging strand
Answer: Correct. Lagging strand synthesis is discontinuous, producing Okazaki fragments.
D. Only in eukaryotes
Explanation: Incorrect. They form in both prokaryotes and eukaryotes.
Q6. The primer for DNA synthesis in cells is usually:
A. DNA made by primase
Explanation: Incorrect. Primase synthesizes short RNA, not DNA, primers.
B. RNA made by primase
Answer: Correct. Primase lays down RNA primers to initiate DNA polymerization.
C. Protein primer
Explanation: Incorrect. Protein primers are not used in chromosomal DNA replication.
D. Deoxynucleoside triphosphate
Explanation: Incorrect. dNTPs are substrates, not primers.
Q7. Proofreading activity in many DNA polymerases is:
A. 5’→3′ exonuclease
Explanation: Incorrect. 5’→3′ exonuclease removes primers, not proofreading.
B. 3’→5′ exonuclease
Answer: Correct. Proofreading removes misincorporated nucleotides.
C. Endonuclease
Explanation: Incorrect. Endonucleases cut within DNA, not proofreading.
D. Helicase
Explanation: Incorrect. Helicase unwinds DNA, unrelated to proofreading.
Q8. In eukaryotes, telomere length is maintained by:
A. DNA ligase
Explanation: Incorrect. Ligase seals nicks but does not extend telomeres.
B. Telomerase
Answer: Correct. Telomerase is a reverse transcriptase that extends telomeric repeats.
C. Topoisomerase II
Explanation: Incorrect. Topoisomerase II relieves supercoils, not telomeres.
D. RNA polymerase II
Explanation: Incorrect. RNAP II transcribes mRNA, not telomeres.
Q9. The TATA box in eukaryotic promoters is recognized by:
A. TFIID (TBP)
Answer: Correct. TBP binds the TATA box to initiate transcription.
B. RNA polymerase I
Explanation: Incorrect. RNAP I transcribes rRNA genes, not TATA.
C. Sigma factor
Explanation: Incorrect. Sigma factors are bacterial promoter recognition proteins.
D. Enhancers
Explanation: Incorrect. Enhancers are DNA sequences, not proteins.
Q10. In bacteria, transcription termination by rho factor requires:
A. A hairpin followed by U-rich tract
Explanation: Incorrect. That is intrinsic termination.
B. ATP-dependent helicase activity
Answer: Correct. Rho uses ATP to dislodge RNAP.
C. TFIID binding
Explanation: Incorrect. TFIID is a eukaryotic factor.
D. Poly(A) polymerase
Explanation: Incorrect. Polyadenylation occurs in eukaryotic mRNAs.
Q11. The 5′ cap of eukaryotic mRNA is:
A. Poly(A) tail
Explanation: Incorrect. The poly(A) tail is at the 3′ end.
B. 7-methylguanosine linked 5′–5′ triphosphate
Answer: Correct. This unique linkage protects mRNA and aids translation.
C. 5-methylcytosine
Explanation: Incorrect. This is DNA methylation.
D. 3′ CCA addition
Explanation: Incorrect. 3′ CCA is added to tRNA, not mRNA.
Q12. Introns are removed from pre-mRNA by:
A. Spliceosome
Answer: Correct. snRNPs and proteins form the spliceosome for splicing.
B. Ribosome
Explanation: Incorrect. Ribosomes translate mRNA, not splice it.
C. Proteasome
Explanation: Incorrect. Proteasomes degrade proteins.
D. Exosome
Explanation: Incorrect. The exosome degrades RNA, not splice it.
Q13. The wobble hypothesis explains:
A. Frameshift mutations
Explanation: Incorrect. Frameshifts result from indels.
B. Redundancy of the genetic code at the third base
Answer: Correct. Wobble allows flexibility at codon’s third base.
C. Initiation of translation
Explanation: Incorrect. Initiation is different.
D. Transcription termination
Explanation: Incorrect. Wobble does not govern termination.
Q14. Shine–Dalgarno sequence is found in:
A. Eukaryotic mRNA
Explanation: Incorrect. Eukaryotes use Kozak sequence.
B. Prokaryotic mRNA
Answer: Correct. It aligns mRNA with 16S rRNA.
C. tRNA
Explanation: Incorrect. Not in tRNA.
D. rRNA only
Explanation: Incorrect. Shine–Dalgarno is on mRNA.
Q15. Peptidyl transferase activity is a function of:
A. Protein enzyme in the large subunit
Explanation: Incorrect. The catalytic site is RNA.
B. rRNA (ribozyme) of the large subunit
Answer: Correct. The ribosome is a ribozyme.
C. Small subunit protein
Explanation: Incorrect. The small subunit decodes.
D. EF-Tu only
Explanation: Incorrect. EF-Tu delivers aa-tRNA, not catalysis.
Q16. An operon is best described as:
A. A single eukaryotic gene with many introns
Explanation: Incorrect. Eukaryotic genes are monocistronic.
B. A cluster of bacterial genes under one promoter
Answer: Correct. Operons coordinate gene expression.
C. A transcription factor
Explanation: Incorrect. TFs regulate operons.
D. A noncoding RNA
Explanation: Incorrect. Operons usually encode proteins.
Q17. In the lac operon, the inducer allolactose binds to:
A. CAP (CRP)
Explanation: Incorrect. CAP binds cAMP.
B. RNA polymerase
Explanation: Incorrect. RNAP does not bind allolactose.
C. Lac repressor
Answer: Correct. Allolactose inactivates repressor to allow transcription.
D. Operator DNA
Explanation: Incorrect. The inducer binds the repressor, not DNA.
Q18. cAMP–CAP complex in the lac operon:
A. Represses transcription in low glucose
Explanation: Incorrect. It activates transcription.
B. Activates transcription when glucose is scarce
Answer: Correct. cAMP–CAP recruits RNAP to promoter.
C. Is unnecessary for lactose metabolism
Explanation: Incorrect. It enhances expression.
D. Binds operator to block RNAP
Explanation: Incorrect. It binds near promoter, not operator.
Q19. A mutation changing a codon to a stop codon is:
A. Missense
Explanation: Incorrect. Missense changes amino acid.
B. Nonsense
Answer: Correct. Nonsense mutations create premature stop codons.
C. Silent
Explanation: Incorrect. Silent does not change amino acid.
D. Frameshift
Explanation: Incorrect. Frameshift involves indels.
Q20. Which DNA repair corrects thymine dimers using light energy in some organisms?
A. Nucleotide excision repair
Explanation: Incorrect. NER excises dimers but not light-dependent.
B. Photoreactivation
Answer: Correct. Photolyase splits dimers using visible light.
C. Base excision repair
Explanation: Incorrect. BER fixes small lesions.
D. Mismatch repair
Explanation: Incorrect. MMR fixes replication errors.
Q21. Which technique amplifies specific DNA sequences in vitro?
A. Northern blotting
Explanation: Incorrect. Northern blot detects RNA.
B. PCR
Answer: Correct. PCR amplifies DNA exponentially.
C. SDS-PAGE
Explanation: Incorrect. Separates proteins.
D. ELISA
Explanation: Incorrect. Detects antigens/antibodies.
Q22. Taq polymerase is isolated from:
A. Thermus aquaticus
Answer: Correct. Thermophilic bacterium provides thermostable enzyme.
B. Escherichia coli
Explanation: Incorrect. E. coli enzymes are not thermostable.
C. Saccharomyces cerevisiae
Explanation: Incorrect. Yeast enzymes differ.
D. Homo sapiens
Explanation: Incorrect. Human polymerases are not used in PCR.
Q23. A vector with genes for β-galactosidase allows:
A. Blue-white screening
Answer: Correct. Disruption of lacZ enables color screening.
B. Replica plating
Explanation: Incorrect. Used for auxotrophy testing.
C. Southern blotting
Explanation: Incorrect. Detects DNA sequences.
D. RFLP typing
Explanation: Incorrect. Not the main role.
Q24. Restriction enzymes typically recognize:
A. Random long sequences
Explanation: Incorrect. They are sequence-specific.
B. Specific palindromic DNA sequences
Answer: Correct. Restriction enzymes cut at palindromic sites.
C. RNA hairpins
Explanation: Incorrect. They act on DNA, not RNA.
D. Protein motifs
Explanation: Incorrect. They do not cut proteins.
Q25. Sticky ends are useful because they:
A. Are resistant to ligases
Explanation: Incorrect. They ligate easily.
B. Facilitate directional cloning via base pairing
Answer: Correct. Overhangs guide insertion orientation.
C. Prevent recombination
Explanation: Incorrect. They promote recombination.
D. Block PCR
Explanation: Incorrect. They do not block PCR.
Q26. cDNA is synthesized from mRNA using:
A. DNA ligase
Explanation: Incorrect. Ligase joins DNA fragments.
B. Reverse transcriptase
Answer: Correct. Reverse transcriptase converts RNA to DNA.
C. RNase H only
Explanation: Incorrect. RNase H degrades RNA, does not synthesize DNA.
D. Topoisomerase
Explanation: Incorrect. Alters DNA topology, not reverse transcription.
Q27. DNA migrates in agarose gel towards the:
A. Cathode due to positive charge
Explanation: Incorrect. DNA is negatively charged.
B. Anode due to negative backbone
Answer: Correct. Phosphate backbone is negative, DNA moves to anode.
C. Cathode due to negative backbone
Explanation: Incorrect. Opposite direction.
D. Does not move
Explanation: Incorrect. DNA moves under electric field.
Q28. Sanger sequencing relies on:
A. ddNTP chain terminators
Answer: Correct. Dideoxynucleotides terminate DNA synthesis.
B. RNase P
Explanation: Incorrect. RNase P processes tRNA.
C. Mass spectrometry of peptides
Explanation: Incorrect. Proteomics, not sequencing.
D. RNA-seq
Explanation: Incorrect. RNA-seq is next-gen sequencing.
Q29. Which blot detects proteins?
A. Southern
Explanation: Incorrect. Southern detects DNA.
B. Northern
Explanation: Incorrect. Northern detects RNA.
C. Western
Answer: Correct. Western blot uses antibodies to detect proteins.
D. Eastern
Explanation: Incorrect. Not standard.
Q30. CRISPR–Cas9 requires a:
A. Guide RNA and PAM
Answer: Correct. gRNA directs Cas9 to DNA adjacent to PAM.
B. DNA primer and ligase
Explanation: Incorrect. Not the targeting mechanism.
C. Only dsDNA breaks without guide
Explanation: Incorrect. Cas9 requires guide RNA.
D. Reverse transcriptase
Explanation: Incorrect. Not involved in CRISPR.
Q31. Real-time qPCR monitors amplification by:
A. Antibody staining
Explanation: Incorrect. Antibodies are not used.
B. Fluorescence during cycles
Answer: Correct. qPCR uses fluorescent dyes or probes.
C. Gel staining after run
Explanation: Incorrect. That’s end-point PCR.
D. Electron microscopy
Explanation: Incorrect. Not used in PCR.
Q32. A housekeeping gene is used in qPCR for:
A. Increasing mutation rate
Explanation: Incorrect. Not a function.
B. Normalization of expression levels
Answer: Correct. Serves as internal control.
C. Inducing apoptosis
Explanation: Incorrect. Not related.
D. Sequencing adapters
Explanation: Incorrect. Not a role in qPCR.
Q33. A plasmid origin of replication determines:
A. Antibiotic resistance
Explanation: Incorrect. Resistance genes provide selection.
B. Copy number and host range
Answer: Correct. ori controls replication in host.
C. Promoter strength
Explanation: Incorrect. Promoter regulates transcription, not replication.
D. Restriction map size only
Explanation: Incorrect. ori has functional role.
Q34. An expression vector must contain:
A. Origin only
Explanation: Incorrect. Insufficient for expression.
B. Promoter and ribosome-binding/translation signals
Answer: Correct. These are required for expression of inserted gene.
C. Telomeres
Explanation: Incorrect. Telomeres are in linear chromosomes.
D. CRISPR array
Explanation: Incorrect. Not required for expression.
Q35. DNA barcoding commonly uses which gene in animals?
A. 16S rRNA
Explanation: Incorrect. Common for bacteria.
B. COI (cytochrome c oxidase I)
Answer: Correct. Standard gene for animal barcoding.
C. GAPDH
Explanation: Incorrect. Housekeeping gene, not barcoding.
D. HBB
Explanation: Incorrect. Hemoglobin beta is not used for barcoding.
Q36. Next-generation sequencing differs from Sanger by:
A. Reading single molecules only
Explanation: Incorrect. Not all platforms.
B. Massively parallel sequencing of many fragments
Answer: Correct. NGS sequences millions simultaneously.
C. No need for DNA polymerase
Explanation: Incorrect. Polymerases are still used.
D. Only RNA templates
Explanation: Incorrect. DNA is also sequenced.
Q37. DNA microarrays primarily measure:
A. Protein abundance
Explanation: Incorrect. Proteomics, not arrays.
B. mRNA expression levels
Answer: Correct. Hybridization intensity reflects transcript abundance.
C. Metabolite concentrations
Explanation: Incorrect. Measured by metabolomics.
D. Chromosome numbers only
Explanation: Incorrect. Not the main use.
Q38. RNA interference (RNAi) uses:
A. dsRNA to trigger mRNA degradation
Answer: Correct. siRNA and miRNA silence mRNA via RISC.
B. ssDNA to cut proteins
Explanation: Incorrect. ssDNA does not cut proteins.
C. rRNA to block replication
Explanation: Incorrect. rRNA is structural.
D. Lipids to digest RNA
Explanation: Incorrect. Not possible.
Q39. A selectable marker in cloning is used to:
A. Visualize DNA bands
Explanation: Incorrect. Stains do that.
B. Select cells that carry the vector
Answer: Correct. Resistance markers help identify transformed cells.
C. Induce transformation
Explanation: Incorrect. Marker does not induce.
D. Sequence the insert
Explanation: Incorrect. Not its role.
Q40. Gibson assembly enables:
A. Random ligation only
Explanation: Incorrect. Not random.
B. Seamless joining of overlapping DNA fragments
Answer: Correct. Exonuclease, polymerase, ligase assemble DNA fragments.
C. RNA splicing
Explanation: Incorrect. Splicing is RNA process.
D. Protein ligation
Explanation: Incorrect. Not for proteins.
Q41. Histone acetylation generally:
A. Condenses chromatin and represses
Explanation: Incorrect. Opposite effect.
B. Relaxes chromatin and activates
Answer: Correct. Acetylation opens chromatin.
C. Degrades histones
Explanation: Incorrect. Does not degrade.
D. Prevents replication
Explanation: Incorrect. Replication still occurs.
Q42. DNA methylation at CpG islands often leads to:
A. Gene activation
Explanation: Incorrect. Usually represses.
B. Gene silencing
Answer: Correct. CpG methylation blocks transcription.
C. Increased recombination
Explanation: Incorrect. Not a direct effect.
D. RNA editing
Explanation: Incorrect. Post-transcriptional.
Q43. Enhancers are:
A. Protein repressors
Explanation: Incorrect. Enhancers are DNA, not proteins.
B. Distant DNA elements that increase transcription
Answer: Correct. Enhancers act at a distance.
C. RNA polymerases
Explanation: Incorrect. RNAP is not enhancer.
D. Promoter cores only
Explanation: Incorrect. Distinct from promoters.
Q44. Mediator complex:
A. Directly synthesizes RNA
Explanation: Incorrect. RNAP II synthesizes.
B. Bridges transcription factors and RNAP II
Answer: Correct. Mediator links regulatory signals.
C. Degrades mRNA
Explanation: Incorrect. Exosome degrades.
D. Replicates DNA
Explanation: Incorrect. Polymerases replicate DNA.
Q45. Heterochromatin is characterized by:
A. High gene expression
Explanation: Incorrect. It is silent.
B. Hypomethylated DNA
Explanation: Incorrect. Usually hypermethylated.
C. H3K9 methylation and compaction
Answer: Correct. Hallmark of heterochromatin.
D. Open DNase I sensitivity
Explanation: Incorrect. Resistant to DNase.
Q46. Insulators (CTCF sites) function to:
A. Enhance transcription globally
Explanation: Incorrect. Not their role.
B. Block enhancer–promoter communication across domains
Answer: Correct. Insulators partition chromatin.
C. Promote translation
Explanation: Incorrect. Translation is cytoplasmic.
D. Methylate DNA
Explanation: Incorrect. Not enzymes.
Q47. X-chromosome inactivation in females involves:
A. Xist lncRNA coating
Answer: Correct. Xist coats and silences one X.
B. Y-linked gene expression increase
Explanation: Incorrect. Not involved.
C. DNA recombination between X and Y
Explanation: Incorrect. Not mechanism.
D. Histone acetylation only
Explanation: Incorrect. Multiple marks are involved.
Q48. miRNAs typically:
A. Increase target protein translation
Explanation: Incorrect. Usually repress.
B. Bind 3′ UTR to repress translation or degrade mRNA
Answer: Correct. miRNAs regulate gene expression.
C. Edit DNA sequences
Explanation: Incorrect. Not their function.
D. Replicate independently
Explanation: Incorrect. Encoded in genome.
Q49. Operons are rare in eukaryotes because:
A. mRNA capping prevents it
Explanation: Incorrect. Not the reason.
B. Eukaryotic mRNAs are generally monocistronic
Answer: Correct. One mRNA → one protein.
C. No promoters exist
Explanation: Incorrect. Promoters exist.
D. Ribosomes cannot bind mRNA
Explanation: Incorrect. Ribosomes do bind.
Q50. Kozak consensus sequence facilitates:
A. DNA replication start
Explanation: Incorrect. Replication origins differ.
B. Eukaryotic translation initiation
Answer: Correct. Kozak enhances AUG recognition.
C. Splice site recognition
Explanation: Incorrect. GU–AG defines introns.
D. Polyadenylation
Explanation: Incorrect. Uses AAUAAA signal.
Q51. Ubiquitination of a protein commonly signals:
A. Nuclear import
Explanation: Incorrect. NLS controls import, not ubiquitin.
B. Proteasomal degradation
Answer: Correct. Polyubiquitin chains target proteins to proteasome.
C. mRNA export
Explanation: Incorrect. Not its role.
D. DNA replication
Explanation: Incorrect. Replication uses polymerases.
Q52. Epigenetic inheritance refers to:
A. Changes in DNA sequence
Explanation: Incorrect. Epigenetics does not alter sequence.
B. Heritable chromatin/RNA states without DNA change
Answer: Correct. Marks like DNA methylation can be inherited.
C. Only mitochondrial genes
Explanation: Incorrect. Not limited to mitochondria.
D. Protein mutations
Explanation: Incorrect. Mutations are genetic, not epigenetic.
Q53. The lac operon operator is bound by:
A. RNAP core enzyme
Explanation: Incorrect. RNAP binds the promoter.
B. LacI repressor
Answer: Correct. LacI binds operator to repress transcription.
C. CAP alone
Explanation: Incorrect. CAP binds near promoter as activator.
D. Rho factor
Explanation: Incorrect. Rho terminates transcription.
Q54. Attenuation regulates the trp operon via:
A. DNA methylation
Explanation: Incorrect. Not the main mechanism.
B. Coupling of transcription and translation in bacteria
Answer: Correct. Leader peptide translation affects RNA structure.
C. Alternative splicing
Explanation: Incorrect. That’s eukaryotic.
D. Protein degradation
Explanation: Incorrect. Not involved.
Q55. Allosteric effectors of transcription factors:
A. Bind DNA directly
Explanation: Incorrect. Effectors bind proteins.
B. Bind proteins to change their activity
Answer: Correct. Effectors alter conformation of TFs.
C. Only increase activity
Explanation: Incorrect. They may repress too.
D. Are always nucleotides
Explanation: Incorrect. Can be many small molecules.
Q56. DNase I hypersensitive sites indicate:
A. Highly condensed chromatin
Explanation: Incorrect. Condensed is DNase-resistant.
B. Accessible regulatory regions
Answer: Correct. DNase hypersensitivity marks open chromatin.
C. Replication origins only
Explanation: Incorrect. Not specific to origins.
D. Centromeric heterochromatin
Explanation: Incorrect. Centromeres are resistant.
Q57. SWI/SNF complexes:
A. Remodel nucleosomes using ATP
Answer: Correct. They reposition nucleosomes.
B. Synthesize DNA
Explanation: Incorrect. Polymerases do this.
C. Degrade histones
Explanation: Incorrect. Proteasome degrades proteins.
D. Cap mRNA
Explanation: Incorrect. Nuclear process unrelated.
Q58. CpG island promoters are often:
A. Methylated in housekeeping genes
Explanation: Incorrect. They are usually unmethylated.
B. Unmethylated and active
Answer: Correct. Active promoters are unmethylated.
C. Absent from vertebrates
Explanation: Incorrect. Common in vertebrate genomes.
D. Only in bacteria
Explanation: Incorrect. CpG islands are eukaryotic.
Q59. Histone H1 is associated with:
A. Nucleosome core particle
Explanation: Incorrect. Core has H2A, H2B, H3, H4.
B. Linker DNA and higher-order compaction
Answer: Correct. H1 binds linker DNA to compact chromatin.
C. DNA replication origins
Explanation: Incorrect. Not a role of H1.
D. RNA splicing
Explanation: Incorrect. Unrelated.
Q60. Topoisomerase II inhibitors (e.g., etoposide) primarily:
A. Increase supercoiling resolution
Explanation: Incorrect. They block resolution.
B. Stabilize double-strand break intermediates causing cytotoxicity
Answer: Correct. Leads to DNA breaks and cell death.
C. Act as polymerases
Explanation: Incorrect. Not enzymes of synthesis.
D. Methylate DNA
Explanation: Incorrect. Not involved.
Q61. Synonymous mutation:
A. Changes amino acid
Explanation: Incorrect. That’s missense.
B. Changes codon without changing amino acid
Answer: Correct. Degeneracy allows same amino acid.
C. Introduces a frameshift
Explanation: Incorrect. Frameshifts are indels.
D. Always harmful
Explanation: Incorrect. Often neutral.
Q62. A transition mutation is:
A. Purine to pyrimidine
Explanation: Incorrect. That’s transversion.
B. Purine to purine or pyrimidine to pyrimidine
Answer: Correct. Transition is within same base class.
C. Any insertion
Explanation: Incorrect. Insertions are not base substitutions.
D. Triplet repeat expansion only
Explanation: Incorrect. Different mechanism.
Q63. Ames test assesses:
A. Antibiotic resistance
Explanation: Incorrect. Not its role.
B. Mutagenicity using bacterial reversion
Answer: Correct. Detects mutagens by His+ reversion.
C. Protein stability
Explanation: Incorrect. Not tested.
D. Virus infectivity
Explanation: Incorrect. Not the aim.
Q64. Mitochondrial DNA is inherited:
A. Maternally in most animals
Answer: Correct. mtDNA usually comes from mother.
B. Paternally
Explanation: Incorrect. Rarely transmitted.
C. Equally from both parents
Explanation: Incorrect. Not biparental.
D. Randomly from neighbors
Explanation: Incorrect. Not possible.
Q65. Exons are:
A. Noncoding regions removed
Explanation: Incorrect. Introns are removed.
B. Coding or UTR segments retained in mRNA
Answer: Correct. Exons remain in mature mRNA.
C. Only protein-coding regions
Explanation: Incorrect. Exons may include UTRs.
D. Intronic repeats
Explanation: Incorrect. Not exons.
Q66. A haplotype is best defined as:
A. A single allele
Explanation: Incorrect. More than one allele.
B. A set of linked alleles on a chromosome segment
Answer: Correct. Haplotype = combination of alleles.
C. A phenotype
Explanation: Incorrect. Phenotype = traits.
D. Aneuploidy
Explanation: Incorrect. Chromosome number change.
Q67. Copy number variation (CNV) refers to:
A. Only SNP changes
Explanation: Incorrect. SNPs are single bases.
B. Segmental duplications/deletions altering dosage
Answer: Correct. CNVs change DNA dosage.
C. Point mutations
Explanation: Incorrect. Not CNV.
D. Methylation status
Explanation: Incorrect. That’s epigenetic.
Q68. Microsatellites are:
A. Long interspersed elements
Explanation: Incorrect. Those are LINEs.
B. Short tandem repeats (1–6 bp units)
Answer: Correct. STRs used in forensics.
C. rRNA genes
Explanation: Incorrect. Not microsatellites.
D. Mitochondrial repeats only
Explanation: Incorrect. Found in nuclear DNA too.
Q69. Nonsense-mediated decay targets mRNAs with:
A. No poly(A) tail
Explanation: Incorrect. Not specific to NMD.
B. Premature stop codons and exon–junction signals
Answer: Correct. PTCs trigger NMD pathway.
C. Too long 5′ UTR
Explanation: Incorrect. Not the trigger.
D. No cap only
Explanation: Incorrect. Not NMD mechanism.
Q70. The genetic code is:
A. Overlapping
Explanation: Incorrect. Code is non-overlapping.
B. Nearly universal and non-overlapping
Answer: Correct. Triplet code applies across life.
C. Ambiguous
Explanation: Incorrect. Each codon = one amino acid.
D. Two-letter
Explanation: Incorrect. Code uses 4 bases.
Q71. Frameshift mutations are often caused by:
A. Synonymous substitutions
Explanation: Incorrect. They don’t shift frame.
B. Insertions or deletions not in multiples of three
Answer: Correct. Alters reading frame.
C. Promoter methylation
Explanation: Incorrect. Epigenetic effect, not frame.
D. Histone acetylation
Explanation: Incorrect. Unrelated.
Q72. A genetic map unit (centimorgan) corresponds to:
A. 1% recombination frequency
Answer: Correct. 1 cM ≈ 1% recombination.
B. 1% GC content
Explanation: Incorrect. Not map unit.
C. 1 Mb distance
Explanation: Incorrect. Physical distance varies.
D. 1 gene
Explanation: Incorrect. Not defined per gene.
Q73. Horizontal gene transfer includes:
A. Transformation, transduction, conjugation
Answer: Correct. Mechanisms of HGT.
B. Mitosis
Explanation: Incorrect. Vertical inheritance.
C. Meiosis
Explanation: Incorrect. Sexual reproduction.
D. Binary fission only
Explanation: Incorrect. Not HGT.
Q74. Transposons move via:
A. Only DNA replication forks
Explanation: Incorrect. Not limited to forks.
B. Cut-and-paste DNA or copy-and-paste via RNA intermediates
Answer: Correct. Two main mechanisms.
C. Protein channels only
Explanation: Incorrect. Proteins assist, but not channels.
D. Membrane vesicles
Explanation: Incorrect. Not mechanism.
Q75. Prions are:
A. Infectious proteins lacking nucleic acids
Answer: Correct. Misfolded proteins propagate disease.
B. RNA viruses
Explanation: Incorrect. They have genomes.
C. Retrotransposons
Explanation: Incorrect. Not proteins.
D. Bacteriophages
Explanation: Incorrect. Phages infect bacteria.
Q76. A gene knockout in mice is commonly achieved by:
A. Random mutagenesis only
Explanation: Incorrect. Less precise.
B. Homologous recombination or CRISPR
Answer: Correct. Targeted disruption removes gene function.
C. RNA editing by ADAR
Explanation: Incorrect. Edits RNA, not DNA.
D. Protein ubiquitination
Explanation: Incorrect. Post-translational modification.
Q77. A linkage disequilibrium (LD) block reflects:
A. Random assortment
Explanation: Incorrect. LD is non-random.
B. Non-random association of alleles in a region
Answer: Correct. LD keeps alleles together.
C. Only coding regions
Explanation: Incorrect. Spans coding and noncoding.
D. Mitochondrial genes
Explanation: Incorrect. mtDNA separate.
Q78. Genome-wide association studies (GWAS) detect:
A. Causation directly
Explanation: Incorrect. GWAS shows correlation.
B. Statistical association between variants and traits
Answer: Correct. SNP-trait links identified.
C. Only rare variants
Explanation: Incorrect. Often common variants.
D. Protein structures
Explanation: Incorrect. Structural biology is different.
Q79. A balanced translocation typically:
A. Changes copy number of genes
Explanation: Incorrect. No net gain/loss.
B. Moves segments without net gain/loss
Answer: Correct. Dosage remains the same.
C. Always lethal
Explanation: Incorrect. Many carriers survive.
D. Only happens in bacteria
Explanation: Incorrect. Occurs in eukaryotes.
Q80. Sickle-cell trait persists due to:
A. Genetic drift only
Explanation: Incorrect. Selection is major factor.
B. Heterozygote advantage against malaria
Answer: Correct. Protects carriers from severe malaria.
C. Founder effect only
Explanation: Incorrect. Not the main driver.
D. Neutral evolution
Explanation: Incorrect. Maintained by selection.
Q81. DNA mismatch repair recognizes:
A. Mature mRNA cap
Explanation: Incorrect. That’s RNA.
B. Replication errors like mispaired bases and small loops
Answer: Correct. MMR fixes replication mistakes.
C. Double-strand breaks only
Explanation: Incorrect. Fixed by HR/NHEJ.
D. Telomere overhangs only
Explanation: Incorrect. Not MMR role.
Q82. Base excision repair starts with:
A. Endonuclease nicking bulky lesion
Explanation: Incorrect. That’s NER.
B. DNA glycosylase removing damaged base
Answer: Correct. Glycosylase excises base.
C. Helicase unwinding lesion
Explanation: Incorrect. Not BER step.
D. DNA ligase only
Explanation: Incorrect. Acts later.
Q83. Nucleotide excision repair is crucial for removing:
A. Oxidized bases only
Explanation: Incorrect. BER removes those.
B. Bulky adducts like thymine dimers
Answer: Correct. NER excises helix-distorting lesions.
C. Correctly paired bases
Explanation: Incorrect. Not removed.
D. Telomeric repeats
Explanation: Incorrect. Not lesions.
Q84. Homologous recombination requires:
A. Sister chromatid or homologous template
Answer: Correct. Uses homology for repair.
B. No template
Explanation: Incorrect. That’s NHEJ.
C. Only ligase
Explanation: Incorrect. Insufficient.
D. Only transposase
Explanation: Incorrect. Not mechanism.
Q85. p53 primarily acts as a:
A. Helicase
Explanation: Incorrect. Does not unwind DNA.
B. Transcription factor inducing cell cycle arrest and apoptosis
Answer: Correct. Tumor suppressor via p21, BAX.
C. Ribosomal protein
Explanation: Incorrect. Not a ribosomal subunit.
D. DNA polymerase
Explanation: Incorrect. Not a polymerase.
Q86. Oncogenes typically are:
A. Loss-of-function in tumor suppressors
Explanation: Incorrect. That defines tumor suppressors.
B. Gain-of-function mutations increasing cell growth
Answer: Correct. Proto-oncogenes become oncogenes.
C. Neutral polymorphisms only
Explanation: Incorrect. They affect growth.
D. Mitochondrial genes only
Explanation: Incorrect. Can be nuclear.
Q87. Reverse transcriptase activity is inherent in:
A. Telomerase
Answer: Correct. Extends telomeres using RNA template.
B. DNA ligase
Explanation: Incorrect. Seals nicks.
C. RNA polymerase II
Explanation: Incorrect. Transcribes mRNA.
D. Topoisomerase I
Explanation: Incorrect. Relieves supercoils.
Q88. A polycistronic mRNA contains:
A. Multiple coding sequences each with its own start/stop
Answer: Correct. Common in prokaryotes.
B. Only one ORF
Explanation: Incorrect. That’s monocistronic.
C. Only introns
Explanation: Incorrect. Bacteria lack introns usually.
D. Only UTRs
Explanation: Incorrect. Has coding regions too.
Q89. Ribosomal A site binds:
A. Peptidyl-tRNA
Explanation: Incorrect. That’s in P site.
B. Aminoacyl-tRNA
Answer: Correct. A site accepts new aa-tRNA.
C. Ejected tRNA
Explanation: Incorrect. E site holds exit tRNA.
D. mRNA cap
Explanation: Incorrect. Cap is in mRNA, not ribosome.
Q90. The start codon AUG codes for:
A. Methionine in eukaryotes and fMet in bacteria
Answer: Correct. AUG initiates translation.
B. Valine in all organisms
Explanation: Incorrect. Valine codons are GUU/GUC/GUA/GUG.
C. Isoleucine
Explanation: Incorrect. AUU/AUC/AUA.
D. Stop
Explanation: Incorrect. AUG is not stop codon.
Q91. Which RNA polymerase transcribes rRNA (28S, 18S, 5.8S) in eukaryotes?
A. RNA Pol I
Answer: Correct. Transcribes major rRNAs in nucleolus.
B. RNA Pol II
Explanation: Incorrect. Transcribes mRNA.
C. RNA Pol III
Explanation: Incorrect. Transcribes tRNA and 5S rRNA.
D. Mitochondrial RNAP only
Explanation: Incorrect. Only for mtDNA.
Q92. A 3′ poly(A) tail in mRNA:
A. Decreases stability
Explanation: Incorrect. It stabilizes.
B. Enhances stability and translation
Answer: Correct. Aids export and translation.
C. Is added co-transcriptionally by RNAP II
Explanation: Incorrect. Added post-transcriptionally.
D. Occurs only in bacteria
Explanation: Incorrect. Mostly in eukaryotes.
Q93. Ribozyme is:
A. A protein enzyme in ribosome
Explanation: Incorrect. Catalytic center is RNA.
B. An RNA molecule with catalytic activity
Answer: Correct. Example: peptidyl transferase.
C. A DNA enzyme only
Explanation: Incorrect. Deoxyribozymes are engineered.
D. A lipoprotein
Explanation: Incorrect. Not definition.
Q94. Allosteric inhibitors of enzymes often:
A. Bind active site only
Explanation: Incorrect. Competitive inhibitors do this.
B. Bind regulatory sites and change conformation
Answer: Correct. They alter enzyme activity indirectly.
C. Increase Vmax always
Explanation: Incorrect. Usually decrease activity.
D. Convert competitive to noncompetitive invariably
Explanation: Incorrect. Mechanisms vary.
Q95. A northern blot probe must be:
A. Protein
Explanation: Incorrect. Probes are nucleic acids.
B. Nucleic acid complementary to target RNA
Answer: Correct. Hybridizes with RNA.
C. Lipid
Explanation: Incorrect. Lipids don’t hybridize.
D. Carbohydrate
Explanation: Incorrect. Carbs don’t hybridize.
Q96. In bacteria, sigma factor’s main role is to:
A. Elongate mRNA
Explanation: Incorrect. Core RNAP elongates.
B. Recognize promoter sequences for initiation
Answer: Correct. Sigma directs RNAP to promoter.
C. Terminate transcription
Explanation: Incorrect. Rho or intrinsic signals terminate.
D. Repair DNA
Explanation: Incorrect. Not a sigma function.
Q97. Southern blotting involves:
A. Transfer of DNA from gel to membrane
Answer: Correct. DNA fragments transferred for hybridization.
B. Transfer of protein to membrane
Explanation: Incorrect. That’s Western blot.
C. RNA to membrane
Explanation: Incorrect. That’s Northern blot.
D. Only in situ hybridization
Explanation: Incorrect. Different technique.
Q98. A tautomeric shift in bases can cause:
A. Increased recombination
Explanation: Incorrect. Not main effect.
B. Mispairing during replication
Answer: Correct. Rare tautomers mispair, causing mutations.
C. Protein denaturation
Explanation: Incorrect. Proteins not affected.
D. RNA splicing
Explanation: Incorrect. Not related.
Q99. Helicase activity requires:
A. ATP hydrolysis
Answer: Correct. Helicases are ATPases that unwind DNA.
B. No energy
Explanation: Incorrect. Energy is required.
C. GTP binding only
Explanation: Incorrect. Most use ATP.
D. Light energy
Explanation: Incorrect. Light used by photolyase, not helicase.
Q100. An anticodon is located on:
A. mRNA
Explanation: Incorrect. Codons are on mRNA.
B. tRNA
Answer: Correct. Anticodon pairs with codon during translation.
C. rRNA
Explanation: Incorrect. rRNA is structural/catalytic.
D. DNA
Explanation: Incorrect. DNA is the template.
