🟢 Part 1: Molecular Basis of Inheritance (Q1–Q25)

Q1. DNA was identified as the transforming principle by

a) Hershey and Chase
b) Griffith
c) Avery, MacLeod, McCarty
d) Watson and Crick

Answer: c) Avery, MacLeod, McCarty
Explanation: They purified the transforming principle from Griffith’s experiment and showed DNase destroys activity → DNA is genetic material.

Q2. The classic blender experiment used bacteriophages labelled with

a) ³²P for protein, ³⁵S for DNA
b) ³⁵S for protein, ³²P for DNA
c) ¹⁴C for protein, ³H for DNA
d) ³H for protein, ¹⁴C for DNA

Answer: b) ³⁵S for protein, ³²P for DNA
Explanation: Sulfur labels protein coats; phosphorus labels DNA, proving DNA enters bacteria (Hershey–Chase).

Q3. The backbone of a DNA strand is made of

a) Nitrogen bases only
b) Ribose and phosphate
c) Deoxyribose and phosphate
d) Bases and amino acids

Answer: c) Deoxyribose and phosphate
Explanation: Sugar–phosphate forms the backbone; bases project inward to pair.

Q4. In B-DNA, the number of base pairs per helical turn is about

a) 8
b) 10
c) 12
d) 14

Answer: b) 10
Explanation: B-DNA has ~10 bp/turn with 3.4 nm pitch and 0.34 nm rise per bp.

Q5. Chargaff’s rule states that in double-stranded DNA

a) A = G and T = C
b) A = T and G = C
c) A = C and G = T
d) Purines = Pyrimidines but A≠T

Answer: b) A = T and G = C
Explanation: Complementary base pairing ensures purine:pyrimidine equality.

Q6. Negative supercoiling in prokaryotic DNA is introduced by

a) Helicase
b) DNA gyrase (topoisomerase II)
c) DNA ligase
d) Primase

Answer: b) DNA gyrase (topoisomerase II)
Explanation: Gyrase introduces negative supercoils to relieve torsional strain.

Q7. DNA replication is called semi-conservative because

a) Both strands are new
b) One old + one new strand in each daughter duplex
c) Old strands remain together
d) Random patchwork forms

Answer: b) One old + one new strand in each daughter duplex
Explanation: Meselson–Stahl (¹⁵N/¹⁴N) showed semi-conservative mechanism.

Q8. The enzyme that synthesizes RNA primers in DNA replication is

a) DNA pol I
b) DNA pol III
c) Primase
d) Telomerase

Answer: c) Primase
Explanation: Primase lays short RNA primers for DNA polymerases to extend.

Q9. Okazaki fragments are formed on the

a) Leading strand only
b) Lagging strand only
c) Both strands
d) RNA template

Answer: b) Lagging strand only
Explanation: Lagging strand synthesized discontinuously opposite fork movement.

Q10. The main replicative polymerase in E. coli is

a) DNA pol I
b) DNA pol II
c) DNA pol III holoenzyme
d) Reverse transcriptase

Answer: c) DNA pol III holoenzyme
Explanation: Pol III has high processivity for bulk DNA synthesis; Pol I removes primers and fills gaps.

Q11. Proofreading activity (3′→5′ exonuclease) is present in

a) DNA pol III
b) DNA pol I
c) Both a and b
d) Neither

Answer: c) Both a and b
Explanation: Both polymerases can excise misincorporated nucleotides.

Q12. Telomerase carries its own

a) DNA template
b) RNA template
c) Protein primer
d) Ligase domain only

Answer: b) RNA template
Explanation: It is an RNA-dependent DNA polymerase extending 3′ ends in eukaryotes.

Q13. In eukaryotes, removal of RNA primer during replication is primarily by

a) RNase H + FEN1
b) DNA pol I
c) Telomerase
d) Topoisomerase I

Answer: a) RNase H + FEN1
Explanation: They remove RNA primers; DNA pol δ fills the gap; ligase seals nick.

Q14. A nucleosome consists of ~

a) DNA wrapped around H1 dimer
b) DNA wrapped around H2A–H2B tetramer
c) 146 bp DNA around histone octamer
d) 200 bp DNA around H1 monomer

Answer: c) 146 bp DNA around histone octamer
Explanation: Octamer = 2×(H2A, H2B, H3, H4); H1 links nucleosomes.

Q15. Heterochromatin is generally

a) Transcriptionally active and loosely packed
b) Transcriptionally inactive and condensed
c) Only prokaryotic
d) Found only at promoters

Answer: b) Transcriptionally inactive and condensed
Explanation: Euchromatin is open/active; heterochromatin is compact/silent.

Q16. The promoter element recognized by σ⁷⁰ in E. coli typically includes

a) −10 (TATAAT) and −35 (TTGACA)
b) CAAT and GC boxes
c) TATA box at −25
d) Poly-A signal

Answer: a) −10 (TATAAT) and −35 (TTGACA)
Explanation: Prokaryotic core promoter elements for RNA pol holoenzyme binding.

Q17. In eukaryotes, mRNA is synthesized by

a) RNA polymerase I
b) RNA polymerase II
c) RNA polymerase III
d) Reverse transcriptase

Answer: b) RNA polymerase II
Explanation: Pol II transcribes mRNA; Pol I rRNA (28S/18S/5.8S), Pol III tRNA and 5S rRNA.

Q18. 5′ capping of eukaryotic mRNA involves addition of

a) Poly-A tail
b) 7-methylguanosine via 5′–5′ triphosphate linkage
c) 3′ CCA
d) 5′ UTR removal

Answer: b) 7-methylguanosine via 5′–5′ triphosphate linkage
Explanation: Cap protects mRNA and aids ribosome binding.

Q19. Removal of introns from pre-mRNA requires

a) Spliceosome recognizing GU–AG rule
b) Rho factor
c) RNase P
d) σ factor

Answer: a) Spliceosome recognizing GU–AG rule
Explanation: Major spliceosome uses snRNPs (U1, U2, U4/U6, U5); most introns have GU–AG ends.

Q20. The Shine–Dalgarno sequence is present in

a) Eukaryotic mRNA
b) Prokaryotic mRNA
c) tRNA
d) rRNA of eukaryotes

Answer: b) Prokaryotic mRNA
Explanation: SD (AGGAGG) aligns mRNA with 16S rRNA for translation initiation.

Q21. The start codon and its amino acid in most organisms is

a) AUG – Methionine (fMet in bacteria)
b) UUG – Leucine
c) GUG – Valine
d) AUA – Isoleucine

Answer: a) AUG – Methionine (fMet in bacteria)
Explanation: AUG codes Met; bacteria use formyl-Met for initiation.

Q22. The genetic code is described as “degenerate” because

a) One codon codes multiple amino acids
b) Multiple codons can specify one amino acid
c) Code varies within one organism
d) Codons overlap in reading

Answer: b) Multiple codons can specify one amino acid
Explanation: Redundancy—e.g., Leu has six codons; but each codon specifies one amino acid.

Q23. Lac operon is maximally expressed when

a) Glucose high, lactose absent
b) Glucose high, lactose present
c) Glucose low, lactose present
d) Glucose absent, lactose absent

Answer: c) Glucose low, lactose present
Explanation: Lactose → allolactose inactivates repressor; low glucose → high cAMP–CAP activates transcription.

Q24. In the trp operon, tryptophan acts as

a) Inducer
b) Corepressor
c) Activator
d) Attenuator RNA

Answer: b) Corepressor
Explanation: Trp binds aporepressor → active repressor binds operator, repressing transcription.

Q25. DNA fingerprinting (profiling) commonly uses

a) rRNA genes
b) VNTR/STR polymorphisms
c) Mitochondrial coding sequences
d) Histone genes

Answer: b) VNTR/STR polymorphisms
Explanation: Variable number tandem repeats/short tandem repeats are highly polymorphic for identity testing.

🟢 Part 2: Molecular Basis of Inheritance (Q26–Q50)

Q26. Which of the following is NOT a property of the genetic code?

a) Degeneracy
b) Overlapping
c) Universal (mostly)
d) Non-ambiguous

Answer: b) Overlapping
Explanation: The genetic code is non-overlapping, read in triplets continuously.

Q27. Which stop codon is called the “opal” codon?

a) UAA
b) UAG
c) UGA
d) AUG

Answer: c) UGA
Explanation: Stop codons: UAA (ochre), UAG (amber), UGA (opal).

Q28. Which enzyme unwinds DNA during replication?

a) DNA polymerase
b) Helicase
c) Ligase
d) Gyrase

Answer: b) Helicase
Explanation: Helicase breaks hydrogen bonds, opening the double helix at the replication fork.

Q29. Which enzyme seals nicks between Okazaki fragments?

a) Primase
b) Ligase
c) Helicase
d) Topoisomerase

Answer: b) Ligase
Explanation: DNA ligase joins DNA fragments by forming phosphodiester bonds.

Q30. Which is a palindromic DNA sequence recognized by EcoRI?

a) GAATTC
b) GGGCCC
c) ATATAT
d) TTTAAA

Answer: a) GAATTC
Explanation: EcoRI cuts between G and A in GAATTC, a palindromic sequence.

Q31. Which type of RNA carries amino acids to the ribosome?

a) mRNA
b) tRNA
c) rRNA
d) snRNA

Answer: b) tRNA
Explanation: tRNA transports amino acids, has anticodon loop for codon recognition.

Q32. Which ribosomal RNA has catalytic (peptidyl transferase) activity?

a) 5S rRNA
b) 16S rRNA
c) 23S rRNA (prokaryotes) / 28S (eukaryotes)
d) 18S rRNA

Answer: c) 23S rRNA (prokaryotes) / 28S (eukaryotes)
Explanation: rRNA in large subunit catalyzes peptide bond formation (ribozyme).

Q33. The lac operon structural genes are:

a) lacI, lacO, lacP
b) lacZ, lacY, lacA
c) CAP, cAMP, lacZ
d) lacO, lacY, lacI

Answer: b) lacZ, lacY, lacA
Explanation: lacZ (β-galactosidase), lacY (permease), lacA (transacetylase).

Q34. The nucleotides in DNA are linked by:

a) Hydrogen bonds
b) Glycosidic bonds
c) Phosphodiester bonds
d) Disulfide bonds

Answer: c) Phosphodiester bonds
Explanation: 3′-OH of one sugar linked to 5′-phosphate of next nucleotide.

Q35. RNA differs from DNA in having:

a) Deoxyribose sugar
b) Thymine
c) Ribose sugar and uracil
d) Both strands

Answer: c) Ribose sugar and uracil
Explanation: RNA has ribose (OH at 2′ carbon) and uracil instead of thymine.

Q36. Hershey–Chase experiment confirmed DNA as genetic material using:

a) E. coli and bacteriophage T2
b) Pneumococcus bacteria
c) Yeast and plasmids
d) Drosophila and fruit flies

Answer: a) E. coli and bacteriophage T2
Explanation: Phages labelled with ³²P (DNA) and ³⁵S (protein) infected E. coli, only DNA entered cells.

Q37. Which DNA form is most common under physiological conditions?

a) A-DNA
b) B-DNA
c) Z-DNA
d) C-DNA

Answer: b) B-DNA
Explanation: B-DNA is the most stable form in normal cells with 10 bp/turn.

Q38. The term “replicon” refers to:

a) A DNA polymerase unit
b) A segment of DNA that replicates from a single origin
c) One Okazaki fragment
d) A gene cluster

Answer: b) A segment of DNA that replicates from a single origin
Explanation: Replicon is a unit of replication, e.g., whole bacterial chromosome.

Q39. What is the function of DNA polymerase I in E. coli?

a) Leading strand synthesis
b) Primer removal and gap filling
c) Helicase activity
d) Proofreading only

Answer: b) Primer removal and gap filling
Explanation: Pol I removes RNA primers via 5′→3′ exonuclease and fills with DNA.

Q40. Reverse transcriptase synthesizes:

a) DNA from DNA
b) DNA from RNA
c) RNA from DNA
d) Protein from RNA

Answer: b) DNA from RNA
Explanation: Retroviruses use reverse transcriptase to make cDNA from RNA genome.

Q41. Satellite DNA refers to:

a) DNA sequences coding proteins
b) Highly repetitive, non-coding DNA sequences
c) rRNA genes
d) Viral DNA in host

Answer: b) Highly repetitive, non-coding DNA sequences
Explanation: Found in centromeres/telomeres; detected by density gradient centrifugation.

Q42. Which enzyme adds nucleotides only to the 3′ end of a growing DNA chain?

a) DNA ligase
b) DNA polymerase
c) RNA polymerase
d) Telomerase

Answer: b) DNA polymerase
Explanation: DNA polymerase can only extend from 3′-OH, not initiate synthesis.

Q43. Which strand of DNA is used as template for RNA synthesis?

a) Coding strand
b) Template strand
c) Both strands simultaneously
d) Either, but only one at a time

Answer: b) Template strand
Explanation: Template strand is read 3′→5′; RNA sequence matches coding strand except U for T.

Q44. Polycistronic mRNA is common in:

a) Prokaryotes
b) Eukaryotes
c) Fungi
d) Viruses only

Answer: a) Prokaryotes
Explanation: One mRNA codes multiple proteins (e.g., lac operon).

Q45. In eukaryotes, poly-A tail is added at:

a) 5′ end of mRNA
b) 3′ end of mRNA
c) Both ends
d) In introns

Answer: b) 3′ end of mRNA
Explanation: Polyadenylation stabilizes mRNA and aids transport from nucleus.

Q46. Which nitrogen base is absent in RNA?

a) Adenine
b) Thymine
c) Cytosine
d) Uracil

Answer: b) Thymine
Explanation: RNA uses uracil instead of thymine.

Q47. Which scientist proposed the Central Dogma of molecular biology?

a) Watson
b) Crick
c) Griffith
d) Avery

Answer: b) Crick
Explanation: Francis Crick proposed DNA → RNA → Protein flow of information.

Q48. The anticodon loop is part of:

a) mRNA
b) tRNA
c) rRNA
d) DNA

Answer: b) tRNA
Explanation: tRNA has anticodon loop complementary to mRNA codons.

Q49. Which of the following RNA has a cloverleaf structure?

a) mRNA
b) rRNA
c) tRNA
d) snRNA

Answer: c) tRNA
Explanation: tRNA folds into cloverleaf structure with acceptor arm and anticodon loop.

Q50. Which DNA sequence acts as termination signal in prokaryotic transcription?

a) Poly-A site
b) Rho-dependent/independent terminators
c) Shine–Dalgarno sequence
d) TATA box

Answer: b) Rho-dependent/independent terminators
Explanation: Transcription ends either by rho factor binding or hairpin loop (intrinsic termination).

🟢 Part 3: Molecular Basis of Inheritance (Q51–Q75)

Q51. Which experiment proved that DNA replication is semiconservative?

a) Griffith’s experiment
b) Avery–MacLeod–McCarty
c) Meselson–Stahl experiment
d) Hershey–Chase experiment

Answer: c) Meselson–Stahl experiment
Explanation: Using heavy isotope ¹⁵N and density gradient centrifugation, they showed each new DNA has one old + one new strand.

Q52. Z-DNA is characterized by

a) Right-handed helix, 10 bp/turn
b) Left-handed helix, 12 bp/turn
c) Left-handed helix, 10 bp/turn
d) Right-handed helix, 12 bp/turn

Answer: b) Left-handed helix, 12 bp/turn
Explanation: Z-DNA is a left-handed helix with zig-zag backbone, formed in GC-rich sequences.

Q53. Which nitrogenous base pairs with adenine in RNA?

a) Thymine
b) Cytosine
c) Uracil
d) Guanine

Answer: c) Uracil
Explanation: In RNA, uracil (U) pairs with adenine (A) instead of thymine.

Q54. Which enzyme catalyzes the joining of DNA fragments by phosphodiester bonds?

a) DNA polymerase
b) DNA ligase
c) RNA polymerase
d) Telomerase

Answer: b) DNA ligase
Explanation: Ligase seals nicks between Okazaki fragments by forming phosphodiester bonds.

Q55. Which statement about genetic code is FALSE?

a) It is universal (almost all organisms use it)
b) It is non-overlapping
c) It is unambiguous
d) Each codon codes for multiple amino acids

Answer: d) Each codon codes for multiple amino acids
Explanation: The code is unambiguous: each codon specifies only one amino acid.

Q56. The enzyme responsible for transcription in prokaryotes is

a) DNA polymerase
b) RNA polymerase (single type)
c) RNA polymerase II
d) Reverse transcriptase

Answer: b) RNA polymerase (single type)
Explanation: Prokaryotes use one RNA polymerase for all RNAs (α₂ββ′σ complex).

Q57. In eukaryotes, tRNA genes are transcribed by

a) RNA polymerase I
b) RNA polymerase II
c) RNA polymerase III
d) Reverse transcriptase

Answer: c) RNA polymerase III
Explanation: Pol III transcribes tRNA and 5S rRNA.

Q58. Which of the following is NOT part of post-transcriptional modification in eukaryotes?

a) 5′ capping
b) Splicing
c) Polyadenylation
d) Shine–Dalgarno sequence

Answer: d) Shine–Dalgarno sequence
Explanation: Shine–Dalgarno is a translation initiation signal in prokaryotes, not RNA processing.

Q59. Exons are

a) Non-coding sequences removed from pre-mRNA
b) Coding sequences retained in mature mRNA
c) Regulatory promoter sequences
d) Intron-like repeats

Answer: b) Coding sequences retained in mature mRNA
Explanation: Exons are expressed sequences that remain after splicing.

Q60. Which of the following is a stop codon?

a) AUG
b) UUU
c) UAA
d) GGG

Answer: c) UAA
Explanation: Stop codons: UAA, UAG, UGA terminate translation.

Q61. The tRNA amino acid attachment site is at the

a) Anticodon loop
b) D loop
c) 3′ CCA end
d) TψC loop

Answer: c) 3′ CCA end
Explanation: Amino acids attach covalently to the 3′ CCA terminus of tRNA.

Q62. Which of the following is the first amino acid incorporated during translation in prokaryotes?

a) Methionine
b) N-formylmethionine
c) Isoleucine
d) Valine

Answer: b) N-formylmethionine
Explanation: fMet-tRNAi initiates protein synthesis in prokaryotes.

Q63. Which DNA polymerase in prokaryotes removes RNA primers?

a) DNA pol I
b) DNA pol II
c) DNA pol III
d) DNA ligase

Answer: a) DNA pol I
Explanation: DNA pol I has 5′→3′ exonuclease activity to remove primers.

Q64. Which RNA is the most abundant in cells?

a) mRNA
b) tRNA
c) rRNA
d) snRNA

Answer: c) rRNA
Explanation: rRNA constitutes ~80% of total cellular RNA.

Q65. Which enzyme relieves supercoiling during DNA replication?

a) DNA polymerase
b) Helicase
c) Topoisomerase (DNA gyrase)
d) Ligase

Answer: c) Topoisomerase (DNA gyrase)
Explanation: Topoisomerase relaxes supercoiling caused by unwinding of DNA.

Q66. Which DNA sequence is rich in AT pairs and acts as replication origin in prokaryotes?

a) OriC
b) Promoter
c) Operator
d) Enhancer

Answer: a) OriC
Explanation: OriC in E. coli contains AT-rich 245 bp, easy to unwind.

Q67. Which scientist gave the “one gene–one enzyme” hypothesis?

a) Watson and Crick
b) Beadle and Tatum
c) Meselson and Stahl
d) Avery and McCarty

Answer: b) Beadle and Tatum
Explanation: Their Neurospora experiments showed genes encode specific enzymes.

Q68. The 16S rRNA is found in

a) Large subunit of prokaryotic ribosome
b) Small subunit of prokaryotic ribosome
c) Small subunit of eukaryotic ribosome
d) Large subunit of eukaryotic ribosome

Answer: b) Small subunit of prokaryotic ribosome
Explanation: 16S rRNA is part of the 30S small ribosomal subunit.

Q69. The wobble hypothesis explains

a) Mutation repair
b) Redundancy in genetic code
c) Crossing over
d) DNA supercoiling

Answer: b) Redundancy in genetic code
Explanation: Wobble at 3rd codon position allows one tRNA to pair with multiple codons.

Q70. In eukaryotes, enhancers are

a) Sequences where repressors bind
b) Regulatory DNA elements that increase transcription
c) Start codons
d) Introns

Answer: b) Regulatory DNA elements that increase transcription
Explanation: Enhancers bind activator proteins to enhance transcription rate.

Q71. In Griffith’s experiment, which strain caused pneumonia in mice?

a) R (rough) strain
b) S (smooth) strain
c) Heat-killed R strain
d) Non-virulent S strain

Answer: b) S (smooth) strain
Explanation: Virulent smooth strain with capsule caused pneumonia; R strain did not.

Q72. Which molecule acts as an inducer in lac operon?

a) Lactose (allolactose)
b) Glucose
c) Galactose
d) cAMP

Answer: a) Lactose (allolactose)
Explanation: Allolactose binds repressor, inactivating it to allow transcription.

Q73. Histones are rich in which amino acids?

a) Glycine and leucine
b) Lysine and arginine
c) Serine and threonine
d) Valine and proline

Answer: b) Lysine and arginine
Explanation: Histones are basic proteins rich in positively charged lysine and arginine, binding negatively charged DNA.

Q74. In Meselson–Stahl experiment, after one generation in ¹⁴N medium, DNA showed

a) Heavy band only
b) Light band only
c) Intermediate band
d) Both heavy and light

Answer: c) Intermediate band
Explanation: Hybrid DNA (¹⁵N/¹⁴N) confirms semiconservative replication.

Q75. Which of the following is a housekeeping gene?

a) LacZ
b) GAPDH
c) Trp operon
d) Hox genes

Answer: b) GAPDH
Explanation: Housekeeping genes like GAPDH are constitutively expressed for basic cell functions.

🟢 Part 4: Molecular Basis of Inheritance (Q76–Q100)

Q76. Which of the following is NOT a component of a nucleotide?

a) Nitrogenous base
b) Phosphate group
c) Pentose sugar
d) Amino acid

Answer: d) Amino acid
Explanation: A nucleotide = nitrogenous base + sugar + phosphate. Amino acids are not part of nucleotides.

Q77. Rosalind Franklin contributed to DNA structure discovery by

a) Isolating DNA
b) X-ray diffraction studies
c) Sequencing DNA
d) Explaining replication

Answer: b) X-ray diffraction studies
Explanation: Her X-ray crystallography images were crucial for Watson & Crick’s DNA model.

Q78. Who proposed the “one gene–one polypeptide” hypothesis?

a) Beadle and Tatum
b) Watson and Crick
c) Hershey and Chase
d) Meselson and Stahl

Answer: a) Beadle and Tatum
Explanation: Modified earlier “one gene–one enzyme” to include polypeptides forming proteins.

Q79. Which type of DNA is found in actively transcribed regions?

a) Heterochromatin
b) Euchromatin
c) Satellite DNA
d) Z-DNA

Answer: b) Euchromatin
Explanation: Euchromatin is loosely packed, transcriptionally active.

Q80. The enzyme that adds new nucleotides during transcription is

a) DNA polymerase
b) RNA polymerase
c) Ligase
d) Telomerase

Answer: b) RNA polymerase
Explanation: RNA polymerase synthesizes RNA from DNA template during transcription.

Q81. Which bond holds complementary bases together in DNA?

a) Peptide bond
b) Phosphodiester bond
c) Hydrogen bond
d) Disulfide bond

Answer: c) Hydrogen bond
Explanation: Hydrogen bonds pair bases: A–T (2 bonds), G–C (3 bonds).

Q82. Which is the initiator codon in protein synthesis?

a) UAA
b) AUG
c) UAG
d) UGA

Answer: b) AUG
Explanation: AUG codes methionine (Met) or N-formylmethionine (fMet in prokaryotes).

Q83. Which of the following DNA bases is a purine?

a) Adenine and Guanine
b) Thymine and Cytosine
c) Cytosine and Guanine
d) Thymine and Adenine

Answer: a) Adenine and Guanine
Explanation: Purines = double-ring bases (A, G); Pyrimidines = single-ring (C, T, U).

Q84. During eukaryotic mRNA processing, introns are removed by

a) DNA polymerase
b) Spliceosome
c) Helicase
d) Ligase

Answer: b) Spliceosome
Explanation: Spliceosome (snRNPs) recognizes GU–AG intron boundaries and removes introns.

Q85. What is the full form of VNTR in DNA fingerprinting?

a) Variable Number Tandem Repeats
b) Various Nucleotide Tandem Regions
c) Verified Non-coding Tandem Repeats
d) Variable Nucleotide Type Regions

Answer: a) Variable Number Tandem Repeats
Explanation: VNTRs are hypervariable sequences used for DNA profiling.

Q86. Which type of mutation involves replacement of a single base pair?

a) Deletion
b) Insertion
c) Substitution
d) Duplication

Answer: c) Substitution
Explanation: Point mutation = substitution of one nucleotide for another.

Q87. If the sequence of coding strand is 5′-ATGCGT-3′, then the mRNA sequence will be

a) 5′-ATGCGT-3′
b) 5′-UACGCA-3′
c) 5′-AUGCGU-3′
d) 3′-TACGCA-5′

Answer: c) 5′-AUGCGU-3′
Explanation: mRNA sequence is same as coding strand (except U for T).

Q88. The enzyme that catalyzes peptide bond formation is

a) Peptidase
b) Peptidyl transferase
c) RNA polymerase
d) Ligase

Answer: b) Peptidyl transferase
Explanation: Ribosomal rRNA (23S/28S) acts as ribozyme catalyzing peptide bond formation.

Q89. Which component brings amino acids to ribosomes during translation?

a) mRNA
b) tRNA
c) rRNA
d) DNA

Answer: b) tRNA
Explanation: Each tRNA carries a specific amino acid and matches codons via anticodons.

Q90. Which scientist used radioactive isotopes to prove DNA is genetic material?

a) Griffith
b) Avery–MacLeod–McCarty
c) Hershey and Chase
d) Meselson and Stahl

Answer: c) Hershey and Chase
Explanation: Phage experiment with ³²P (DNA) and ³⁵S (protein) proved DNA is genetic material.

Q91. The length of one complete turn of B-DNA is

a) 3.4 nm
b) 2.0 nm
c) 0.34 nm
d) 34 nm

Answer: a) 3.4 nm
Explanation: One turn = 10 base pairs × 0.34 nm rise per bp = 3.4 nm.

Q92. Which RNA acts as an adapter molecule during translation?

a) mRNA
b) tRNA
c) rRNA
d) snRNA

Answer: b) tRNA
Explanation: Crick called tRNA the “adapter molecule” linking codons and amino acids.

Q93. The function of DNA ligase in DNA replication is to

a) Add nucleotides continuously
b) Seal Okazaki fragments
c) Open the DNA helix
d) Remove primers

Answer: b) Seal Okazaki fragments
Explanation: Ligase joins DNA fragments on lagging strand by phosphodiester bond.

Q94. Which process copies genetic information from DNA to RNA?

a) Translation
b) Transcription
c) Replication
d) Reverse transcription

Answer: b) Transcription
Explanation: RNA polymerase synthesizes RNA transcript from DNA template.

Q95. Which is NOT a property of the genetic code?

a) Triplet
b) Commaless
c) Ambiguous
d) Universal

Answer: c) Ambiguous
Explanation: The code is unambiguous (one codon = one amino acid).

Q96. Which enzyme removes RNA primers in eukaryotic DNA replication?

a) DNA polymerase α
b) RNase H and FEN1
c) DNA ligase
d) Topoisomerase

Answer: b) RNase H and FEN1
Explanation: RNase H + flap endonuclease (FEN1) remove primers; DNA pol δ fills gaps.

Q97. In prokaryotes, rho factor is associated with

a) Initiation of replication
b) Proofreading
c) Transcription termination
d) Translation elongation

Answer: c) Transcription termination
Explanation: Rho factor terminates transcription at specific sites (rho-dependent termination).

Q98. The process of RNA editing involves

a) Adding introns
b) Alteration of nucleotide sequence of RNA
c) Addition of 5′ cap
d) Addition of poly-A tail

Answer: b) Alteration of nucleotide sequence of RNA
Explanation: RNA editing modifies RNA post-transcriptionally (insertion, deletion, substitution).

Q99. Which enzyme is responsible for synthesizing telomeres?

a) Ligase
b) Primase
c) Telomerase
d) Gyrase

Answer: c) Telomerase
Explanation: Telomerase extends chromosome ends using its RNA template.

Q100. Who proposed the operon model of gene regulation?

a) Jacob and Monod
b) Watson and Crick
c) Griffith
d) Beadle and Tatum

Answer: a) Jacob and Monod
Explanation: Jacob & Monod proposed operon model (lac operon) to explain regulation in prokaryotes.

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