DNA

DNA stands for:
a) Deoxyribose Nucleic Acid
b) Deoxyribonucleic Acid
c) Di-nuclear Acid
d) Dimeric Nucleic Acid
Answer: b
Explanation: DNA = Deoxyribonucleic Acid. (BPSC 63rd)
The structure of DNA was discovered by:
a) Darwin and Wallace
b) Watson and Crick
c) Mendel and Morgan
d) Hershey and Chase
Answer: b
Explanation: Watson and Crick proposed the double helix model in 1953. (BPSC 64th)
The sugar present in DNA is:
a) Glucose
b) Ribose
c) Deoxyribose
d) Sucrose
Answer: c
Explanation: DNA contains deoxyribose sugar. (BPSC Teacher 2023)
DNA is found primarily in:
a) Ribosomes
b) Golgi bodies
c) Nucleus
d) Lysosomes
Answer: c
Explanation: DNA is mostly located inside the nucleus. (BPSC 65th)
Which nitrogen base is not present in DNA?
a) Adenine
b) Cytosine
c) Thymine
d) Uracil
Answer: d
Explanation: Uracil is found in RNA, not DNA. (BPSC 67th)
Which base pairs with Adenine in DNA?
a) Cytosine
b) Thymine
c) Guanine
d) Uracil
Answer: b
Explanation: Adenine pairs with Thymine via two hydrogen bonds. (BPSC 66th)
DNA replication occurs in:
a) Metaphase
b) Interphase
c) Anaphase
d) Telophase
Answer: b
Explanation: DNA replicates during the S-phase of interphase. (BPSC CDPO)
A nucleotide consists of:
a) Base + Sugar
b) Sugar + Phosphate
c) Sugar + Base + Phosphate
d) Protein + Base
Answer: c
Explanation: A nucleotide = base + sugar + phosphate group. (BPSC AE)
Which of the following is a purine base?
a) Adenine
b) Cytosine
c) Thymine
d) Uracil
Answer: a
Explanation: Adenine and Guanine are purines. (BPSC 68th)
The number of base pairs in human DNA is approximately:
a) 10 million
b) 3.2 billion
c) 1 lakh
d) 2.5 million
Answer: b
Explanation: The human genome contains about 3.2 billion base pairs.

NCERT-Based Questions (Q11–30)

DNA is composed of how many strands?
a) One
b) Two
c) Three
d) Variable
Answer: b
Explanation: DNA has a double helix structure—two complementary strands.
The shape of DNA molecule is:
a) Zig-zag
b) Circular
c) Helical
d) Spherical
Answer: c
Explanation: DNA has a helical shape (double helix).
The backbone of DNA is formed by:
a) Nitrogen bases
b) Phosphate and sugar
c) Phosphate and base
d) Protein and sugar
Answer: b
Explanation: Sugar-phosphate chains form the DNA backbone.
Guanine pairs with:
a) Thymine
b) Adenine
c) Cytosine
d) Uracil
Answer: c
Explanation: G ≡ C (three hydrogen bonds).
A gene is a segment of:
a) Protein
b) RNA
c) Chromosome
d) DNA
Answer: d
Explanation: Genes are functional segments of DNA.
In prokaryotes, DNA is:
a) Double-stranded and circular
b) Single-stranded
c) Linear
d) None
Answer: a
Explanation: Bacterial DNA is double-stranded and circular.
What is the function of DNA?
a) Energy production
b) Structural support
c) Genetic information storage
d) Transport
Answer: c
Explanation: DNA stores and transmits hereditary information.
The enzyme that unzips DNA during replication is:
a) Ligase
b) Helicase
c) Polymerase
d) Nuclease
Answer: b
Explanation: Helicase breaks hydrogen bonds to unwind DNA.
What holds the nitrogenous bases together in DNA?
a) Covalent bonds
b) Hydrogen bonds
c) Ionic bonds
d) Metallic bonds
Answer: b
Explanation: Hydrogen bonds connect base pairs.
Number of hydrogen bonds between A–T pair:
a) 1
b) 2
c) 3
d) 4
Answer: b
Explanation: A-T pairs are bonded by 2 hydrogen bonds.
DNA was first isolated by:
a) Watson
b) Crick
c) Friedrich Miescher
d) Hershey
Answer: c
Explanation: Miescher discovered "nuclein" in 1869.
Base pairing rule is also known as:
a) Mendel’s rule
b) Chargaff’s rule
c) Darwin’s rule
d) Crick’s rule
Answer: b
Explanation: A=T and G≡C – Chargaff’s base ratio rule.
DNA replication is:
a) Conservative
b) Semi-conservative
c) Dispersive
d) Degenerative
Answer: b
Explanation: Each daughter DNA has one old and one new strand.
The total number of chromosomes in a human somatic cell is:
a) 23
b) 46
c) 92
d) 22
Answer: b
Explanation: 46 chromosomes = 23 pairs.
Which organelle contains DNA apart from nucleus?
a) Ribosome
b) Mitochondria
c) Golgi body
d) Lysosome
Answer: b
Explanation: Mitochondria have their own DNA (mtDNA).
The smallest unit of DNA is:
a) Chromosome
b) Gene
c) Codon
d) Nucleotide
Answer: d
Explanation: Nucleotide = base + sugar + phosphate.
Number of different nitrogenous bases in DNA:
a) 2
b) 3
c) 4
d) 5
Answer: c
Explanation: Adenine, Guanine, Cytosine, Thymine.
Base pair rule in DNA:
a) A=T, G=C
b) A=C, T=G
c) A=G, T=C
d) A=U, G=T
Answer: a
Explanation: Complementary base pairing rule.
What is a gene?
a) Protein unit
b) RNA unit
c) DNA sequence coding for protein
d) Cytoplasm
Answer: c
Explanation: Genes contain instructions to make proteins.
DNA polymerase helps in:
a) Joining fragments
b) Synthesizing new DNA strand
c) Proofreading
d) All of the above
Answer: d
Explanation: DNA polymerase performs multiple roles in replication.

Predicted/Reference Book-Based Questions (Q31–50)

DNA fingerprinting is based on:
a) Protein sequencing
b) Unique base sequences
c) Enzyme activity
d) RNA length
Answer: b
Explanation: Unique base pair patterns identify individuals.
DNA is made up of:
a) Amino acids
b) Fatty acids
c) Nucleotides
d) Monosaccharides
Answer: c
Explanation: DNA is a polymer of nucleotides.
DNA double helix was shown using:
a) Microscope
b) X-ray diffraction
c) Spectrometer
d) Electrophoresis
Answer: b
Explanation: Rosalind Franklin used X-ray diffraction.
In DNA, which base is not found in RNA?
a) Adenine
b) Uracil
c) Guanine
d) Thymine
Answer: d
Explanation: DNA has thymine; RNA has uracil instead.
Human genome project was completed in:
a) 2001
b) 2003
c) 2005
d) 2010
Answer: b
Explanation: Human Genome Project ended in April 2003.
DNA is located in:
a) Only nucleus
b) Nucleus and mitochondria
c) Cytoplasm
d) Endoplasmic reticulum
Answer: b
Explanation: DNA is found in nucleus and mitochondria.
DNA → RNA → Protein is called:
a) RNA theory
b) Central dogma
c) Cell theory
d) Mendel's law
Answer: b
Explanation: Central dogma explains gene expression.
DNA stores genetic code in the form of:
a) Codons
b) Enzymes
c) Hormones
d) Sugars
Answer: a
Explanation: Codons are triplets of bases coding amino acids.
The enzyme used to join DNA fragments:
a) Ligase
b) Helicase
c) Topoisomerase
d) Endonuclease
Answer: a
Explanation: Ligase joins Okazaki fragments.
A triplet code in DNA is called:
a) Anticodon
b) Ribosome
c) Codon
d) Histone
Answer: c
Explanation: Codon = 3-base sequence coding one amino acid.
The bond between sugar and phosphate in DNA:
a) Peptide bond
b) Hydrogen bond
c) Phosphodiester bond
d) Ionic bond
Answer: c
Explanation: Phosphodiester bonds connect sugar and phosphate.
The packaging proteins around which DNA wraps are:
a) Actin
b) Myosin
c) Histones
d) Globulins
Answer: c
Explanation: Histones help compact DNA into chromatin.
DNA molecule is stabilized by:
a) Peptide bonds
b) Hydrogen bonds
c) Glycosidic bonds
d) Phospholipid layers
Answer: b
Explanation: Base pairs are held by H-bonds.
The total amount of DNA in a diploid human cell:
a) 3.2 million bp
b) 3.2 billion bp
c) 46 million bp
d) 100 thousand bp
Answer: b
Explanation: Each diploid cell has about 3.2 billion base pairs.
DNA forms the hereditary material in:
a) Only humans
b) All prokaryotes
c) All eukaryotes
d) Both b and c
Answer: d
Explanation: DNA is hereditary material in almost all organisms.
Which component of DNA provides specificity?
a) Sugar
b) Phosphate
c) Nitrogen base sequence
d) Histones
Answer: c
Explanation: Base sequence defines genetic code.
The pyrimidines in DNA are:
a) Adenine and Thymine
b) Cytosine and Thymine
c) Adenine and Guanine
d) Guanine and Cytosine
Answer: b
Explanation: C and T are pyrimidines.
Purines are:
a) A and C
b) G and T
c) A and G
d) C and T
Answer: c
Explanation: Adenine and Guanine are purines.
The complementary sequence of 5'-ATGC-3' is:
a) 5'-ATGC-3'
b) 5'-CGTA-3'
c) 3'-TACG-5'
d) 5'-TACG-3'
Answer: c
Explanation: Base pairing rule: A-T, G-C.
DNA replication is catalyzed by:
a) DNA helicase
b) DNA polymerase
c) DNA ligase
d) All of these
Answer: d
Explanation: Replication involves multiple enzymes.