🌸 Chapter 5
Molecular Basis Of Inheritance
(MCQs)
1. Who discovered DNA?
A) Watson and Crick
B) Miescher
C) Griffith
D) Hershey and Chase
Answer: B
🧠 Friedrich Miescher (1869) discovered nuclein (DNA) from pus cells.
2. DNA is mainly found in which part
of eukaryotic cell?
A) Nucleus
B) Cytoplasm
C) Ribosomes
D) Golgi body
Answer: A
🧠 DNA is stored in the nucleus as chromosomes in eukaryotes.
3. Which sugar is present in DNA?
A) Ribose
B) Deoxyribose
C) Glucose
D) Fructose
Answer: B
🧠 DNA has deoxyribose sugar; RNA has ribose sugar.
4. Which base is not found in RNA?
A) Adenine
B) Uracil
C) Thymine
D) Cytosine
Answer: C
🧠 RNA contains Uracil (U) instead of Thymine (T).
5. DNA and RNA are polymers of:
A) Amino acids
B) Fatty acids
C) Nucleotides
D) Monosaccharides
Answer: C
🧠 Both are polynucleotides formed by repeating nucleotide units.
6. The purines are:
A) Adenine and Thymine
B) Adenine and Guanine
C) Cytosine and Thymine
D) Cytosine and Uracil
Answer: B
🧠 Purines are double-ringed bases (A and G).
7. The number of hydrogen bonds
between G and C is:
A) 2
B) 3
C) 4
D) 1
Answer: B
🧠 G–C pair has 3 H-bonds; A–T has 2.
8. DNA strands run:
A) Parallel
B) Antiparallel
C) Perpendicular
D) Randomly
Answer: B
🧠 One runs 5′→3′, other 3′→5′.
9. The pitch of DNA helix is:
A) 3.4 nm
B) 2.0 nm
C) 0.34 nm
D) 1.5 nm
Answer: A
🧠 10 base pairs = 3.4 nm in one complete turn.
10. The distance between two base
pairs is:
A) 0.34 nm
B) 3.4 nm
C) 2.0 nm
D) 34 nm
Answer: A
🧠 Each base pair is separated by 0.34 nm.
11. The total length of DNA in a
human diploid cell is approximately:
A) 1.1 m
B) 2.2 m
C) 3.4 m
D) 4.4 m
Answer: B
🧠 2.2 meters long — fits into nucleus by packaging.
12. DNA packaging proteins in
eukaryotes are:
A) Histones
B) Albumins
C) Globulins
D) Keratins
Answer: A
🧠 Histones (basic proteins) help in nucleosome formation.
13. A nucleosome consists of DNA wrapped
around:
A) 6 histones
B) 8 histones
C) 10 histones
D) 4 histones
Answer: B
🧠 Histone octamer = 2 each of H2A, H2B, H3, H4.
14. Linker DNA length is
approximately:
A) 146 bp
B) 200 bp
C) 54 bp
D) 20 bp
Answer: B
🧠 Each nucleosome + linker = about 200 base pairs.
15. In prokaryotes, DNA is:
A) Circular and naked
B) Linear and histone-bound
C) Linear and naked
D) Circular and histone-bound
Answer: A
🧠 Bacterial DNA is circular and not associated with histones.
16. Griffith worked on which organism?
A) E. coli
B) Streptococcus pneumoniae
C) Drosophila
D) Tobacco mosaic virus
Answer: B
🧠 He demonstrated the ‘transforming principle’ in S. pneumoniae.
17. Griffith’s experiment proved:
A) DNA is genetic material
B) Proteins carry heredity
C) Transformation occurs in bacteria
D) RNA is genetic material
Answer: C
🧠 Transformation was first observed by Griffith.
18. Avery, MacLeod, and McCarty
proved:
A) Protein is genetic material
B) DNA is genetic material
C) RNA is genetic material
D) None
Answer: B
🧠 They confirmed that DNA is the ‘transforming principle’.
19. Hershey and Chase used
radioactive isotopes:
A) ³²P and ³⁵S
B) ¹⁴C and ¹⁵N
C) ³⁵Cl and ³²S
D) ¹⁵O and ¹⁴N
Answer: A
🧠 ³²P labels DNA; ³⁵S labels protein.
20. Hershey–Chase experiment used:
A) Plant virus
B) Bacteriophage
C) Fungi
D) Yeast
Answer: B
🧠 T2 bacteriophage infecting E. coli.
21. DNA replication is:
A) Conservative
B) Semi-conservative
C) Dispersive
D) Random
Answer: B
🧠 Each new DNA has one old and one new strand.
22. Meselson–Stahl experiment used
isotope:
A) ¹⁴C
B) ¹⁵N
C) ³⁵S
D) ³²P
Answer: B
🧠 They used heavy nitrogen (¹⁵N) in E. coli DNA.
23. The enzyme that joins Okazaki
fragments:
A) DNA polymerase
B) DNA ligase
C) RNA polymerase
D) Primase
Answer: B
🧠 DNA ligase seals nicks between fragments.
24. The direction of DNA synthesis
is:
A) 3′→5′
B) 5′→3′
C) Both
D) Random
Answer: B
🧠 DNA polymerase adds nucleotides in 5′→3′ direction.
25. The enzyme that unwinds DNA:
A) Ligase
B) Helicase
C) Polymerase
D) Topoisomerase
Answer: B
🧠 Helicase unwinds DNA double helix at replication fork.
26. Okazaki fragments are formed on:
A) Leading strand
B) Lagging strand
C) Both strands
D) Template strand
Answer: B
🧠 Lagging strand is synthesized discontinuously.
27. RNA primer is synthesized by:
A) Ligase
B) Primase
C) Helicase
D) Polymerase I
Answer: B
🧠 Primase synthesizes short RNA primers.
28. The main enzyme of DNA
replication:
A) DNA polymerase III
B) DNA polymerase I
C) Ligase
D) Primase
Answer: A
🧠 DNA polymerase III performs major elongation in prokaryotes.
29. The enzyme that removes RNA
primers:
A) DNA polymerase I
B) Ligase
C) RNA polymerase
D) Helicase
Answer: A
🧠 It has 5′→3′ exonuclease activity to remove primers.
30. Central dogma of molecular
biology was given by:
A) Watson
B) Crick
C) Griffith
D) Hershey
Answer: B
🧠 Information flow: DNA → RNA → Protein.
31. Transcription is the process of:
A) DNA → DNA
B) DNA → RNA
C) RNA → Protein
D) RNA → DNA
Answer: B
🧠 Transcription forms RNA from DNA.
32. Enzyme responsible for
transcription:
A) DNA polymerase
B) RNA polymerase
C) Ligase
D) Helicase
Answer: B
🧠 RNA polymerase synthesizes RNA using DNA template.
33. In prokaryotes, RNA polymerase
has subunits:
A) 1
B) 2
C) 4 + σ factor
D) 5 + ρ factor
Answer: C
🧠 Core enzyme + sigma (σ) factor for initiation.
34. In eukaryotes, mRNA is formed
by:
A) RNA pol I
B) RNA pol II
C) RNA pol III
D) DNA pol I
Answer: B
🧠 RNA polymerase II synthesizes mRNA.
35. 5′ cap of mRNA contains:
A) Poly-A tail
B) Methyl guanosine triphosphate
C) Poly-U tail
D) Poly-G tail
Answer: B
🧠 Capping protects mRNA from degradation.
36. Intron removal from RNA is
called:
A) Splicing
B) Ligation
C) Translation
D) Replication
Answer: A
🧠 Introns (non-coding) are removed, exons joined.
37. Translation is:
A) DNA → RNA
B) RNA → Protein
C) DNA → Protein
D) Protein → RNA
Answer: B
🧠 mRNA → polypeptide chain.
38. Start codon in mRNA is:
A) AUG
B) UAA
C) UGA
D) UAG
Answer: A
🧠 AUG codes for methionine.
39. Stop codons are:
A) UAA, UAG, UGA
B) AUG, UAA, UAG
C) UGA, GGG, AAA
D) None
Answer: A
🧠 They signal termination of translation.
40. Genetic code is:
A) Triplet
B) Commaless
C) Universal
D) All of these
Answer: D
🧠 It’s triplet, commaless, degenerate, and universal.
41. The number of possible codons
is:
A) 16
B) 20
C) 61
D) 64
Answer: D
🧠 4³ = 64 codons.
42. The number of amino acid–coding
codons:
A) 64
B) 61
C) 60
D) 3
Answer: B
🧠 61 sense codons, 3 stop codons.
43. The tRNA has site for:
A) Codon
B) Anticodon
C) Ribosome
D) DNA
Answer: B
🧠 Anticodon recognizes codon on mRNA.
44. Ribosomes are sites for:
A) Transcription
B) Translation
C) Replication
D) Mutation
Answer: B
🧠 Protein synthesis occurs on ribosomes.
45. The 3′ end of tRNA carries:
A) Codon
B) Anticodon
C) Amino acid
D) DNA sequence
Answer: C
🧠 tRNA 3′ end attaches to specific amino acid.
46. The enzyme that charges tRNA:
A) Ligase
B) Aminoacyl tRNA synthetase
C) Polymerase
D) Kinase
Answer: B
🧠 It attaches amino acid to corresponding tRNA.
47. Lac operon was discovered by:
A) Watson and Crick
B) Jacob and Monod
C) Avery and McCarty
D) Meselson and Stahl
Answer: B
🧠 They proposed operon model in 1961.
48. The lac operon is:
A) Inducible
B) Repressible
C) Constitutive
D) None
Answer: A
🧠 It is activated in presence of lactose.
49. Structural genes of lac operon:
A) Z, Y, A
B) X, Y, Z
C) P, O, Z
D) I, P, O
Answer: A
🧠 They code for enzymes for lactose metabolism.
50. Repressor gene of lac operon is:
A) P
B) O
C) I
D) Z
Answer: C
🧠 ‘i’ gene produces repressor protein.
51. The promoter site in lac operon
is the binding site for:
A) RNA polymerase
B) Repressor
C) Lactose
D) Regulator gene
Answer: A
🧠 Promoter is the sequence where RNA polymerase binds to initiate
transcription.
52. The operator gene in lac operon
controls:
A) Transcription of structural genes
B) Synthesis of lactose
C) Activity of repressor
D) Production of RNA polymerase
Answer: A
🧠 Operator acts as an on/off switch for structural gene
transcription.
53. In absence of lactose, the
repressor binds to:
A) Promoter
B) Operator
C) Z gene
D) RNA polymerase
Answer: B
🧠 Repressor protein blocks RNA polymerase binding to the operator
region.
54. In presence of lactose, the
repressor becomes:
A) Active
B) Inactive
C) Denatured
D) None
Answer: B
🧠 Lactose (inducer) binds to repressor → inactivates it →
transcription starts.
55. In lac operon, β-galactosidase
is coded by:
A) Z gene
B) Y gene
C) A gene
D) I gene
Answer: A
🧠 Z gene produces β-galactosidase enzyme that hydrolyzes lactose.
56. The function of permease enzyme
is:
A) Converts lactose to glucose
B) Allows lactose to enter the cell
C) Synthesizes repressor
D) Joins Okazaki fragments
Answer: B
🧠 Permease increases permeability of cell membrane to lactose.
57. The A gene in lac operon codes
for:
A) β-galactosidase
B) Permease
C) Transacetylase
D) RNA polymerase
Answer: C
🧠 A gene → transacetylase enzyme (function not well-defined).
58. The lac operon is turned on in
presence of:
A) Glucose
B) Lactose
C) Both glucose and lactose
D) None
Answer: B
🧠 Lactose acts as inducer, removing repressor from operator.
59. The operon concept mainly
explains:
A) DNA replication
B) Gene regulation in prokaryotes
C) Protein folding
D) RNA modification
Answer: B
🧠 Operon model explains transcriptional level gene regulation.
60. Which of the following is not
a structural gene in lac operon?
A) Z
B) Y
C) A
D) I
Answer: D
🧠 ‘i’ is regulator gene, not a structural gene.
61. The term "genetic
code" refers to:
A) The sequence of amino acids in protein
B) Sequence of nucleotides in mRNA
C) The set of rules by which codons specify amino acids
D) Genetic instructions in chromosomes
Answer: C
🧠 Genetic code links codon (on mRNA) to specific amino acids.
62. Who deciphered the first codon?
A) Watson and Crick
B) Har Gobind Khorana
C) Nirenberg and Matthaei
D) Jacob and Monod
Answer: C
🧠 They discovered that UUU codes for phenylalanine.
63. Which codon does not code for
any amino acid?
A) AUG
B) UGA
C) GCU
D) UUU
Answer: B
🧠 UGA, UAG, UAA are stop codons.
64. AUG codon codes for:
A) Valine
B) Methionine
C) Proline
D) Serine
Answer: B
🧠 AUG = start codon; codes for methionine.
65. Genetic code is universal
because:
A) Same codon specifies same amino acid in all organisms
B) Every organism has same DNA length
C) Proteins are same everywhere
D) None
Answer: A
🧠 Universality of genetic code shows common ancestry.
66. The degeneracy of genetic code
means:
A) More than one codon codes for same amino acid
B) One codon codes for multiple amino acids
C) Codons are ambiguous
D) Codons overlap
Answer: A
🧠 Example: Leucine coded by six codons.
67. The wobble hypothesis explains:
A) Mutation
B) Degeneracy of code
C) Codon recognition flexibility
D) DNA replication
Answer: C
🧠 Third base of codon may pair loosely — flexibility in pairing.
68. Who proposed the “one gene-one
enzyme” hypothesis?
A) Beadle and Tatum
B) Watson and Crick
C) Jacob and Monod
D) Nirenberg and Khorana
Answer: A
🧠 Beadle & Tatum proved each gene controls one enzyme.
69. The flow of genetic information
is:
A) Protein → RNA → DNA
B) DNA → RNA → Protein
C) RNA → DNA → Protein
D) Protein → DNA → RNA
Answer: B
🧠 Described by Crick’s Central Dogma.
70. Which type of RNA carries
genetic message from DNA?
A) rRNA
B) tRNA
C) mRNA
D) snRNA
Answer: C
🧠 mRNA carries codons from DNA to ribosomes.
71. Ribosomal RNA forms the:
A) Template for mRNA
B) Structural and catalytic part of ribosome
C) Adapter molecule
D) Regulatory RNA
Answer: B
🧠 rRNA forms structural backbone of ribosomes.
72. The adapter molecule in protein
synthesis is:
A) mRNA
B) tRNA
C) rRNA
D) DNA
Answer: B
🧠 tRNA carries amino acids and matches codons via anticodons.
73. Which bond links amino acids in
a protein chain?
A) Hydrogen bond
B) Ionic bond
C) Peptide bond
D) Phosphodiester bond
Answer: C
🧠 Peptide bond forms between –COOH of one and –NH₂ of another amino
acid.
74. A triplet of bases in mRNA is
called:
A) Gene
B) Codon
C) Anticodon
D) Exon
Answer: B
🧠 Codon corresponds to one amino acid.
75. Each codon consists of:
A) 2 bases
B) 3 bases
C) 4 bases
D) 5 bases
Answer: B
🧠 Triplet code — 3 nucleotides = 1 codon.
76. The process of copying DNA into
mRNA is called:
A) Translation
B) Replication
C) Transcription
D) Transformation
Answer: C
🧠 Transcription is the first step of gene expression.
77. Splicing occurs in:
A) Prokaryotes
B) Eukaryotes
C) Viruses
D) Bacteria
Answer: B
🧠 Only eukaryotic genes have introns removed during RNA processing.
78. The non-coding sequences in
eukaryotic genes are called:
A) Exons
B) Introns
C) Codons
D) Genes
Answer: B
🧠 Introns are removed during mRNA maturation.
79. Exons are:
A) Non-coding sequences
B) Coding sequences
C) Introns
D) Mutations
Answer: B
🧠 Exons express information — retained in mRNA.
80. The term “intron” was given by:
A) Nirenberg
B) Crick
C) Gilbert
D) Watson
Answer: C
🧠 Walter Gilbert coined the term intron.
81. The Human Genome Project aimed
to:
A) Create artificial DNA
B) Sequence entire human DNA
C) Produce cloned humans
D) Study genetic diseases only
Answer: B
🧠 HGP mapped and sequenced 3 billion base pairs.
82. HGP was completed in:
A) 1995
B) 2000
C) 2003
D) 2005
Answer: C
🧠 Human Genome Project was completed in April 2003.
83. Total number of genes found in
human genome:
A) ~1 lakh
B) 20,000–25,000
C) 50,000
D) 2,000
Answer: B
🧠 Less than 2% of genome codes for proteins.
84. Which technique is used in DNA
fingerprinting?
A) PCR
B) Southern blotting
C) Western blotting
D) Northern blotting
Answer: B
🧠 Southern blotting separates DNA fragments and detects specific
sequences.
85. DNA fingerprinting is based on:
A) Genetic code
B) DNA replication
C) Polymorphism in DNA sequences
D) Translation
Answer: C
🧠 DNA variation among individuals is detected.
86. The scientist who developed DNA
fingerprinting:
A) Watson
B) Crick
C) Alec Jeffreys
D) Khorana
Answer: C
🧠 Sir Alec Jeffreys introduced it in 1985.
87. VNTR stands for:
A) Variable Number Tandem Repeats
B) Variable Nucleotide Transcribed Region
C) Variant Nucleic Tandem RNA
D) Very New Tandem Repeat
Answer: A
🧠 VNTRs are short repeating DNA sequences used in fingerprinting.
88. DNA fingerprinting is used in:
A) Crime detection
B) Paternity testing
C) Evolutionary studies
D) All of these
Answer: D
🧠 It identifies individuals uniquely based on DNA.
89. Which enzyme cuts DNA at
specific sites?
A) Ligase
B) Restriction endonuclease
C) Polymerase
D) Helicase
Answer: B
🧠 Restriction enzymes recognize specific sequences and cleave DNA.
90. DNA ligase joins DNA fragments
by forming:
A) Peptide bond
B) Hydrogen bond
C) Phosphodiester bond
D) Ionic bond
Answer: C
🧠 It seals nicks between sugar-phosphate backbones.
91. The most stable form of DNA is:
A) A-DNA
B) B-DNA
C) Z-DNA
D) C-DNA
Answer: B
🧠 B-DNA is right-handed and most commonly found in cells.
92. Z-DNA is:
A) Left-handed helix
B) Right-handed helix
C) Triple helix
D) Single-stranded
Answer: A
🧠 Z-DNA has left-handed coiling, GC-rich regions.
93. The human DNA is packed with:
A) Histones
B) Lipids
C) Proteins and RNA
D) Carbohydrates
Answer: A
🧠 Histones are positively charged and bind negatively charged DNA.
94. The basic repeating unit of
chromatin is:
A) Gene
B) Nucleosome
C) Chromatid
D) Centromere
Answer: B
🧠 DNA wrapped around histone octamer = nucleosome.
95. One nucleosome contains
approximately:
A) 50 bp DNA
B) 146 bp DNA
C) 300 bp DNA
D) 10 bp DNA
Answer: B
🧠 Around 146 bp of DNA winds around histone core.
96. The number of base pairs in one
complete DNA turn is:
A) 10
B) 20
C) 5
D) 15
Answer: A
🧠 10 base pairs = 1 helical turn.
97. The diameter of DNA double helix
is:
A) 2.0 nm
B) 3.4 nm
C) 0.34 nm
D) 4.0 nm
Answer: A
🧠 The uniform diameter of B-DNA is 2 nm.
98. DNA replication occurs in which
phase of cell cycle?
A) G₁ phase
B) S phase
C) G₂ phase
D) M phase
Answer: B
🧠 S (synthetic) phase — DNA duplication happens.
99. Which molecule acts as genetic
material in some viruses?
A) DNA
B) RNA
C) Both
D) None
Answer: B
🧠 RNA viruses (like HIV, TMV) have RNA as genetic material.
100. The first genetic material
according to RNA world hypothesis was:
A) DNA
B) RNA
C) Protein
D) Lipid
Answer: B
🧠 RNA could both store information and catalyze reactions — believed
to be first genetic material.
