Biological role of nucleic acids MCQs With Answer

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Biological role of nucleic acids MCQs With Answer are essential for B. Pharm students to master how DNA and RNA store, transmit, and regulate genetic information. This concise, keyword-rich introduction focuses on nucleic acids, nucleotides, replication, transcription, translation, gene expression, mutations, repair mechanisms, and nucleic-acid-based therapeutics like antisense oligonucleotides and siRNA. Understanding structure-function relationships, enzymatic players (polymerases, nucleases, topoisomerases), and laboratory techniques (PCR, gel electrophoresis, reverse transcription) prepares pharmacy students for pharmacogenomics, drug development, and molecular diagnostics. The following 50 MCQs with answers deepen conceptual knowledge and exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which sugar is present in RNA nucleotides?

  • Deoxyribose
  • Ribose
  • Fructose
  • Glucose

Correct Answer: Ribose

Q2. The bond that links nucleotides in a DNA strand is called:

  • Glycosidic bond
  • Peptide bond
  • Phosphodiester bond
  • Hydrogen bond

Correct Answer: Phosphodiester bond

Q3. Which base is found in RNA but not in DNA?

  • Adenine
  • Guanine
  • Uracil
  • Thymine

Correct Answer: Uracil

Q4. The central dogma of molecular biology describes information flow from:

  • Protein → RNA → DNA
  • DNA → RNA → Protein
  • RNA → DNA → Protein
  • DNA → Protein → RNA

Correct Answer: DNA → RNA → Protein

Q5. During DNA replication, which enzyme synthesizes the new DNA strand?

  • RNA polymerase
  • DNA ligase
  • DNA polymerase
  • Topoisomerase

Correct Answer: DNA polymerase

Q6. Which RNA type carries amino acids to the ribosome during translation?

  • mRNA
  • rRNA
  • tRNA
  • snRNA

Correct Answer: tRNA

Q7. Which of the following best describes a gene?

  • A segment of DNA that encodes a functional product
  • A lipid molecule in membranes
  • A type of ribosomal protein
  • A carbohydrate storage unit

Correct Answer: A segment of DNA that encodes a functional product

Q8. Complementary base pairing in DNA is due to:

  • Covalent bonding between bases
  • Hydrophobic interactions only
  • Hydrogen bonding between purines and pyrimidines
  • Ionic bonds with the phosphate backbone

Correct Answer: Hydrogen bonding between purines and pyrimidines

Q9. Reverse transcriptase is an enzyme used by:

  • Bacteria for DNA replication
  • Retroviruses to synthesize DNA from RNA
  • Ribosomes during translation
  • Mitochondria for ATP production

Correct Answer: Retroviruses to synthesize DNA from RNA

Q10. The start codon in mRNA that signals initiation of translation is:

  • UAA
  • AUG
  • UGA
  • UAG

Correct Answer: AUG

Q11. Which enzyme removes RNA primers during DNA replication in prokaryotes?

  • DNA polymerase I
  • DNA polymerase III
  • DNA ligase
  • Primase

Correct Answer: DNA polymerase I

Q12. A frameshift mutation results from:

  • A base substitution that preserves reading frame
  • Insertion or deletion of nucleotides not multiple of three
  • Loss of an entire chromosome
  • Methylation of cytosine residues

Correct Answer: Insertion or deletion of nucleotides not multiple of three

Q13. Which technique is commonly used to amplify a specific DNA fragment?

  • Southern blotting
  • PCR (Polymerase Chain Reaction)
  • ELISA
  • Mass spectrometry

Correct Answer: PCR (Polymerase Chain Reaction)

Q14. In eukaryotes, primary RNA transcripts are processed by:

  • Splicing, 5′ capping, and 3′ polyadenylation
  • Only methylation
  • Proteolytic cleavage into amino acids
  • Direct translation without modification

Correct Answer: Splicing, 5′ capping, and 3′ polyadenylation

Q15. Which of the following is a double-stranded RNA virus feature?

  • Uses host DNA polymerase for replication
  • Has segmented genome in some families
  • Always integrates into host genome
  • Contains deoxyribose sugars

Correct Answer: Has segmented genome in some families

Q16. Which class of drugs targets topoisomerases involved in DNA replication?

  • Beta-lactams
  • Topoisomerase inhibitors like fluoroquinolones and anticancer agents
  • Statins
  • Proton pump inhibitors

Correct Answer: Topoisomerase inhibitors like fluoroquinolones and anticancer agents

Q17. Antisense oligonucleotides exert therapeutic effects by:

  • Blocking ribosome assembly on rRNA
  • Binding complementary mRNA to inhibit translation or alter splicing
  • Increasing DNA methylation globally
  • Degrading proteins directly

Correct Answer: Binding complementary mRNA to inhibit translation or alter splicing

Q18. Which nucleic acid base pairing is correct?

  • A pairs with C in DNA
  • G pairs with T in DNA
  • A pairs with T and G pairs with C in DNA
  • U pairs with C in DNA

Correct Answer: A pairs with T and G pairs with C in DNA

Q19. Telomerase adds telomeric repeats using which template?

  • mRNA template
  • DNA template provided by lagging strand
  • Intrinsic RNA component of telomerase
  • tRNA primer

Correct Answer: Intrinsic RNA component of telomerase

Q20. Which repair mechanism corrects thymine dimers caused by UV light?

  • Base excision repair
  • Nucleotide excision repair
  • Mismatch repair
  • Non-homologous end joining

Correct Answer: Nucleotide excision repair

Q21. In prokaryotes, transcription and translation are coupled because:

  • Transcription occurs in the nucleus
  • Ribosomes initiate translation before transcription finishes
  • mRNA is highly processed before translation
  • Prokaryotes lack mRNA

Correct Answer: Ribosomes initiate translation before transcription finishes

Q22. Which component of chromatin directly binds DNA?

  • Histone proteins
  • RNA polymerase
  • Ribosomal proteins
  • Lipid molecules

Correct Answer: Histone proteins

Q23. A nonsense mutation results in:

  • A single amino acid substitution
  • A premature stop codon leading to truncated protein
  • An expanded polyglutamine tract
  • No change in amino acid sequence

Correct Answer: A premature stop codon leading to truncated protein

Q24. Small interfering RNA (siRNA) functions by:

  • Enhancing translation of target mRNA
  • Sequence-specific degradation of target mRNA via RISC
  • Inhibiting DNA replication directly
  • Acting as a primer for DNA polymerase

Correct Answer: Sequence-specific degradation of target mRNA via RISC

Q25. Which technique separates DNA fragments by size?

  • Western blotting
  • Gel electrophoresis
  • Chromatography for small molecules only
  • Flow cytometry

Correct Answer: Gel electrophoresis

Q26. Plasmids are useful in molecular cloning because they:

  • Are linear DNA molecules that cannot replicate
  • Act as vectors that can replicate independently in bacteria
  • Are composed solely of RNA
  • Cannot carry foreign genes

Correct Answer: Act as vectors that can replicate independently in bacteria

Q27. Which enzyme joins Okazaki fragments on the lagging strand?

  • DNA helicase
  • DNA ligase
  • Primase
  • Topoisomerase II

Correct Answer: DNA ligase

Q28. The wobble hypothesis explains:

  • Redundancy in the genetic code allowing multiple codons per amino acid
  • Why DNA is double stranded
  • How ribosomes synthesize lipids
  • How histones bind DNA

Correct Answer: Redundancy in the genetic code allowing multiple codons per amino acid

Q29. CpG methylation in gene promoters commonly leads to:

  • Increased transcriptional activity
  • Transcriptional silencing or reduced gene expression
  • More efficient translation
  • Immediate mRNA degradation

Correct Answer: Transcriptional silencing or reduced gene expression

Q30. Which molecule is the template for protein synthesis?

  • tRNA
  • mRNA
  • rRNA
  • DNA directly

Correct Answer: mRNA

Q31. In Sanger sequencing, which reagent causes chain termination?

  • Normal deoxynucleotides (dNTPs)
  • Dideoxynucleotides (ddNTPs)
  • RNA nucleotides (rNTPs)
  • ATP only

Correct Answer: Dideoxynucleotides (ddNTPs)

Q32. Which polymerase synthesizes mRNA in eukaryotic cells?

  • DNA polymerase I
  • RNA polymerase II
  • RNA polymerase I
  • DNA polymerase III

Correct Answer: RNA polymerase II

Q33. Homologous recombination is important for:

  • Error-prone repair of single-strand breaks
  • Accurate repair of double-strand breaks using a homologous template
  • Protein degradation in lysosomes
  • Carbohydrate metabolism

Correct Answer: Accurate repair of double-strand breaks using a homologous template

Q34. Which is a property of mitochondrial DNA?

  • Linear chromosomes with histones
  • Maternally inherited and circular in many species
  • Encoded in the nucleus exclusively
  • Not used in energy production

Correct Answer: Maternally inherited and circular in many species

Q35. The Shine-Dalgarno sequence is involved in:

  • Eukaryotic transcription initiation
  • Prokaryotic translation initiation by aligning mRNA with ribosome
  • Spliceosome assembly in eukaryotes
  • DNA methylation

Correct Answer: Prokaryotic translation initiation by aligning mRNA with ribosome

Q36. Which enzyme relieves supercoiling ahead of the replication fork?

  • DNA helicase
  • Topoisomerase
  • Primase
  • Ligase

Correct Answer: Topoisomerase

Q37. A missense mutation leads to:

  • Insertion of a premature stop codon
  • Change of one amino acid to another in the protein
  • Frame shift in the reading frame
  • No change in protein sequence

Correct Answer: Change of one amino acid to another in the protein

Q38. Which RNA component is part of the ribosome’s catalytic site (peptidyl transferase)?

  • mRNA
  • rRNA
  • tRNA
  • snRNA

Correct Answer: rRNA

Q39. Gene expression regulation by small RNAs in bacteria often uses:

  • microRNAs packaged in exosomes
  • Antisense small RNAs that affect mRNA stability or translation
  • Histone acetylation
  • Alternative splicing

Correct Answer: Antisense small RNAs that affect mRNA stability or translation

Q40. Which statement about plasmid copy number is correct?

  • All plasmids have the same copy number in a cell
  • Copy number varies and affects gene expression levels of plasmid-borne genes
  • High copy number plasmids cannot be used in cloning
  • Copy number is irrelevant for recombinant protein production

Correct Answer: Copy number varies and affects gene expression levels of plasmid-borne genes

Q41. Transcription factors bind to DNA to:

  • Hydrolyze nucleotides
  • Regulate gene transcription positively or negatively
  • Translate mRNA into protein
  • Package DNA into histones

Correct Answer: Regulate gene transcription positively or negatively

Q42. Which molecule provides energy for peptide bond formation during translation?

  • ATP directly in the ribosome
  • GTP used by translation factors
  • Glucose oxidation
  • cAMP

Correct Answer: GTP used by translation factors

Q43. A polycistronic mRNA is typically found in:

  • Eukaryotic cells with introns
  • Prokaryotic operons encoding multiple proteins from one mRNA
  • Human mitochondrial transcripts only
  • Only in viral DNA genomes

Correct Answer: Prokaryotic operons encoding multiple proteins from one mRNA

Q44. Nonsense-mediated mRNA decay (NMD) functions to:

  • Enhance translation of long mRNAs
  • Degrade mRNAs containing premature stop codons to prevent truncated proteins
  • Repair DNA double-strand breaks
  • Promote ribosomal frameshifting

Correct Answer: Degrade mRNAs containing premature stop codons to prevent truncated proteins

Q45. Which technique detects specific DNA sequences using labeled probes after gel transfer?

  • Western blot
  • Northern blot
  • Southern blot
  • ELISA

Correct Answer: Southern blot

Q46. The anticodon of a tRNA pairs with:

  • The DNA codon in the nucleus
  • The mRNA codon during translation
  • Ribosomal RNA exclusively
  • Another tRNA molecule

Correct Answer: The mRNA codon during translation

Q47. Which of the following is an example of epigenetic regulation?

  • Point mutation in a coding exon
  • DNA methylation leading to gene silencing
  • Deletion of an entire gene
  • Substitution of one amino acid

Correct Answer: DNA methylation leading to gene silencing

Q48. CRISPR-Cas systems function in bacteria primarily as:

  • Protein synthesis machinery
  • Adaptive immune systems providing acquired resistance to phages via nucleic acid targeting
  • Energy-generating organelles
  • Lipid biosynthesis enzymes

Correct Answer: Adaptive immune systems providing acquired resistance to phages via nucleic acid targeting

Q49. Which statement about the genetic code is true?

  • It is ambiguous; a single codon can code for multiple amino acids
  • It is nearly universal and degenerate, with multiple codons for most amino acids
  • It varies entirely between bacteria and humans
  • Stop codons code for specific amino acids

Correct Answer: It is nearly universal and degenerate, with multiple codons for most amino acids

Q50. Base excision repair primarily corrects:

  • Large deletion events
  • Small, non-helix-distorting base lesions like deaminated cytosine
  • Double-strand chromosomal breaks
  • Errors in mRNA splicing

Correct Answer: Small, non-helix-distorting base lesions like deaminated cytosine

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