Assertion (A): DNA is the genetic material in most organisms.
Reason (R): DNA is chemically less stable than RNA.
Answer: (C) A is true, but R is false.
Explanation: DNA is the genetic material due to its stability,
not its instability. RNA is less stable and more prone to mutations.
Assertion (A): The purine and pyrimidine bases in DNA are
complementary to each other.
Reason (R): Complementary base pairing is due to hydrogen
bonding between specific pairs of bases.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Adenine pairs with thymine via 2 hydrogen bonds,
and guanine pairs with cytosine via 3 hydrogen bonds.
Assertion (A): In prokaryotes, transcription and translation
occur simultaneously.
Reason (R): Prokaryotes lack a nuclear membrane.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: In prokaryotes, the absence of a nuclear membrane
allows ribosomes to attach to mRNA as it is being transcribed.
Assertion (A): In eukaryotes, mRNA undergoes splicing before
translation.
Reason (R): Eukaryotic genes contain introns and exons.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Splicing removes introns from pre-mRNA, leaving
only the exons for translation.
Assertion (A): The enzyme DNA polymerase synthesizes DNA in the
5' to 3' direction.
Reason (R): DNA polymerase can add nucleotides only to a free
3'-OH group.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: DNA polymerase requires a primer with a free 3'-OH
group to initiate DNA synthesis.
Assertion (A): RNA primer is required for DNA replication.
Reason (R): DNA polymerase cannot initiate the synthesis of a
new strand de novo.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: RNA primer provides the free 3'-OH group necessary
for DNA polymerase to begin synthesis.
Assertion (A): The lagging strand in DNA replication is
synthesized as Okazaki fragments.
Reason (R): DNA polymerase synthesizes DNA only in the 5' to 3'
direction.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The lagging strand is synthesized discontinuously
due to the unidirectional nature of DNA polymerase.
Assertion (A): DNA replication is semi-conservative.
Reason (R): Each daughter DNA molecule consists of one parental
and one newly synthesized strand.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Experiments by Meselson and Stahl confirmed the
semi-conservative model of replication.
Assertion (A): The genetic code is universal.
Reason (R): All living organisms use the same codons to specify
amino acids.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The universality of the genetic code indicates a
common evolutionary origin.
Assertion (A): The genetic code is degenerate.
Reason (R): Some amino acids are specified by more than one
codon.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Degeneracy reduces the impact of mutations on
protein sequences.
Assertion (A): RNA polymerase binds to the promoter region of a
gene to initiate transcription.
Reason (R): Promoter regions have specific sequences recognized
by RNA polymerase.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The promoter region provides the binding site for
RNA polymerase.
Assertion (A): tRNA acts as an adapter molecule in translation.
Reason (R): tRNA carries amino acids to the ribosome and
matches them to the mRNA codons.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The anticodon on tRNA base-pairs with the codon on
mRNA, ensuring the correct amino acid is added.
Assertion (A): DNA has thymine instead of uracil.
Reason (R): Thymine provides greater stability to the DNA
molecule.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Thymine is less prone to hydrolysis than uracil,
enhancing DNA stability.
Assertion (A): The lac operon is an inducible operon.
Reason (R): The presence of lactose induces the expression of
genes for lactose metabolism.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Lactose acts as an inducer by binding to the
repressor, allowing transcription.
Assertion (A): DNA ligase is essential for DNA replication.
Reason (R): DNA ligase joins Okazaki fragments on the lagging
strand.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: DNA ligase forms phosphodiester bonds to seal
nicks between Okazaki fragments.
Assertion (A): RNA polymerase II is responsible for the
synthesis of mRNA in eukaryotes.
Reason (R): RNA polymerase II binds to the enhancer regions of
DNA to initiate transcription.
Answer: (C) A is true, but R is false.
Explanation: RNA polymerase II binds to the promoter, not the
enhancer. Enhancers regulate transcription but do not directly bind RNA
polymerase.
Assertion (A): DNA replication in eukaryotes occurs only during
the S phase of the cell cycle.
Reason (R): The S phase ensures that DNA is replicated once per
cell cycle.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The S phase is dedicated to DNA synthesis,
ensuring accurate genome duplication.
Assertion (A): DNA helicase unwinds the DNA helix during
replication.
Reason (R): DNA helicase breaks the hydrogen bonds between
complementary bases.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Helicase is essential for separating DNA strands
by breaking hydrogen bonds.
Assertion (A): The stop codons UAA, UAG, and UGA do not code
for any amino acids.
Reason (R): Stop codons terminate translation by releasing the
polypeptide chain.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Stop codons signal the end of translation, and no
tRNA matches them.
Assertion (A): Prokaryotic mRNA does not undergo splicing.
Reason (R): Prokaryotic genes are uninterrupted, lacking
introns.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Introns are absent in prokaryotes, so splicing is
unnecessary.
Assertion (A): The Hershey-Chase experiment proved that DNA is
the genetic material.
Reason (R): Radioactive sulfur was found inside the bacterial
cells.
Answer: (C) A is true, but R is false.
Explanation: Radioactive phosphorus, not sulfur, was found in
bacterial cells, showing DNA is the genetic material.
Assertion (A): DNA is negatively charged due to phosphate
groups in its backbone.
Reason (R): Phosphate groups in DNA are acidic and release H+
ions.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The phosphate backbone of DNA gives it a negative
charge, essential for gel electrophoresis.
Assertion (A): DNA gyrase is essential for replication in
prokaryotes.
Reason (R): DNA gyrase relieves supercoiling ahead of the
replication fork.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: DNA gyrase reduces tension caused by unwinding the
DNA helix.
Assertion (A): Histones are basic proteins.
Reason (R): Histones are rich in positively charged amino
acids, lysine, and arginine.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The positive charge of histones facilitates their
binding to negatively charged DNA.
Assertion (A): The nucleosome is the fundamental unit of
chromatin.
Reason (R): Each nucleosome is composed of histone proteins and
DNA wrapped around them.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: A nucleosome consists of ~200 base pairs of DNA
wrapped around histone octamers.
Assertion (A): The genetic code is non-overlapping.
Reason (R): Each codon is read sequentially during translation.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Each codon specifies one amino acid without
overlapping sequences.
Assertion (A): Polyadenylation is a post-transcriptional
modification in eukaryotes.
Reason (R): A poly-A tail is added to the 5' end of mRNA.
Answer: (C) A is true, but R is false.
Explanation: The poly-A tail is added to the 3' end of mRNA,
not the 5' end.
Assertion (A): Griffith’s experiment demonstrated the
phenomenon of transformation.
Reason (R): Heat-killed S-strain bacteria converted R-strain
bacteria into a virulent form.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Transformation was observed when R-strain bacteria
acquired genetic material from heat-killed S-strain bacteria.
Assertion (A): In transcription, only one strand of DNA is used
as a template.
Reason (R): The antisense strand of DNA provides the template
for mRNA synthesis.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Transcription uses the antisense strand to produce
a complementary RNA sequence.
Assertion (A): Telomerase prevents the shortening of
chromosomes.
Reason (R): Telomerase adds repetitive nucleotide sequences to
the ends of chromosomes.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Telomerase counteracts the loss of DNA at the ends
of linear chromosomes during replication.
Assertion (A): DNA ligase is required for joining Okazaki
fragments during replication.
Reason (R): DNA polymerase synthesizes DNA only in the 3' to 5'
direction.
Answer: (C) A is true, but R is false.
Explanation: DNA ligase joins Okazaki fragments on the lagging
strand, while DNA polymerase synthesizes DNA in the 5' to 3' direction.
Assertion (A): RNA is less stable than DNA.
Reason (R): RNA has ribose sugar, which contains a hydroxyl
group at the 2' position.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The 2' hydroxyl group in ribose makes RNA more
reactive and prone to hydrolysis, reducing its stability.
Assertion (A): The lac operon is an example of an inducible
operon.
Reason (R): The lac operon is activated in the presence of
glucose.
Answer: (C) A is true, but R is false.
Explanation: The lac operon is induced in the presence of
lactose, not glucose, and repressed when glucose is present.
Assertion (A): In prokaryotes, transcription and translation
are coupled.
Reason (R): Prokaryotes lack a defined nucleus.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Since prokaryotes lack a nuclear membrane,
translation can begin while transcription is still ongoing.
Assertion (A): In DNA, the two strands are held together by
covalent bonds.
Reason (R): Base pairing between adenine and thymine involves
hydrogen bonds.
Answer: (C) A is false, but R is true.
Explanation: The two strands of DNA are held together by
hydrogen bonds between complementary bases, not covalent bonds.
Assertion (A): tRNA acts as an adaptor molecule in translation.
Reason (R): tRNA recognizes codons on mRNA and carries specific
amino acids.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: tRNA has an anticodon that pairs with mRNA codons
and an amino acid attachment site.
Assertion (A): DNA fingerprinting uses repetitive sequences in
the genome.
Reason (R): Repetitive sequences vary greatly among
individuals.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Variable number tandem repeats (VNTRs) are used in
DNA fingerprinting because they are unique to individuals.
Assertion (A): The enzyme reverse transcriptase synthesizes DNA
from an RNA template.
Reason (R): Reverse transcriptase is used by retroviruses like
HIV.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Reverse transcriptase allows retroviruses to
convert their RNA into DNA, integrating it into the host genome.
Assertion (A): Chargaff's rule states that A = T and G = C in
DNA.
Reason (R): Purines and pyrimidines pair in a 1:1 ratio in the
DNA double helix.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Chargaff's rule reflects the base-pairing between
purines (A, G) and pyrimidines (T, C).
Assertion (A): In eukaryotes, pre-mRNA undergoes capping at the
5' end.
Reason (R): Capping protects mRNA from degradation and aids in
ribosome binding.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The 5' cap stabilizes mRNA and facilitates
translation initiation.
Assertion (A): The genetic code is degenerate.
Reason (R): Multiple codons can code for the same amino acid.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: The degeneracy of the genetic code allows for
codon redundancy.
Assertion (A): DNA replication is semiconservative.
Reason (R): Each new DNA molecule consists of one parental and
one newly synthesized strand.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Experimental evidence from the Meselson-Stahl
experiment supports semiconservative replication.
Assertion (A): Promoters are regulatory sequences upstream of
genes.
Reason (R): Promoters are recognized by RNA polymerase to
initiate transcription.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Promoters provide the binding site for RNA
polymerase to start transcription.
Assertion (A): Eukaryotic mRNA is monocistronic.
Reason (R): Each eukaryotic mRNA typically codes for a single
polypeptide.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Unlike prokaryotic mRNA, eukaryotic mRNA usually
translates into a single protein.
Assertion (A): Exons are coding sequences in eukaryotic genes.
Reason (R): Introns are removed during RNA splicing.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: Exons remain in the mature mRNA after introns are
spliced out.
Assertion (A): DNA replication in prokaryotes begins at
multiple origins.
Reason (R): Prokaryotes have a circular DNA molecule.
Answer: (C) A is false, but R is true.
Explanation: Prokaryotic DNA replication begins at a single
origin of replication.
Assertion (A): DNA polymerase I has proofreading ability.
Reason (R): It has 5' to 3' exonuclease activity.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: DNA polymerase I can remove mismatched nucleotides
and replace them with the correct ones.
Assertion (A): Translation occurs in the nucleus of eukaryotic
cells.
Reason (R): Ribosomes are present in the cytoplasm.
Answer: (D) A is false, but R is true.
Explanation: Translation occurs in the cytoplasm, not the
nucleus, in eukaryotes.
Assertion (A): DNA methylation can repress gene expression.
Reason (R): Methylation of promoter regions prevents
transcription factor binding.
Answer: (A) Both A and R are true, and R is the correct
explanation of A.
Explanation: DNA methylation alters chromatin structure,
silencing genes.
Assertion (A): Okazaki fragments are formed on the leading
strand during DNA replication.
Reason (R): DNA synthesis on the lagging strand is
discontinuous.
Answer: (C) A is false, but R is true.
Explanation: Okazaki fragments are specific to the lagging
strand due to its discontinuous replication.