ROUTERA


Chapter 6 Molecular basis of Inheritance

Class 12th Biology Chapter MCQs


1. What is the shape of the DNA molecule?

  • A) Helical
  • B) Linear
  • C) Circular
  • D) Spherical

Answer: A
Explanation: DNA has a helical structure, commonly referred to as a double helix.


2. Who discovered the structure of DNA?

  • A) James Watson and Francis Crick
  • B) Rosalind Franklin and Maurice Wilkins
  • C) Charles Darwin
  • D) Gregor Mendel

Answer: A
Explanation: James Watson and Francis Crick, with the help of Rosalind Franklin’s X-ray diffraction images, discovered the structure of DNA in 1953.


3. Which of the following is NOT a nitrogenous base found in DNA?

  • A) Adenine
  • B) Guanine
  • C) Uracil
  • D) Cytosine

Answer: C
Explanation: Uracil is found in RNA, not DNA. DNA contains thymine instead of uracil.


4. In a DNA molecule, adenine always pairs with:

  • A) Guanine
  • B) Thymine
  • C) Cytosine
  • D) Uracil

Answer: B
Explanation: In DNA, adenine (A) always pairs with thymine (T) via two hydrogen bonds.


5. Which of the following enzymes is responsible for unwinding the DNA double helix during replication?

  • A) DNA polymerase
  • B) Ligase
  • C) Helicase
  • D) Primase

Answer: C
Explanation: Helicase unwinds the DNA double helix by breaking the hydrogen bonds between the base pairs.


6. What is the function of DNA polymerase?

  • A) To unwind the DNA
  • B) To synthesize RNA
  • C) To synthesize a complementary strand of DNA
  • D) To add primers

Answer: C
Explanation: DNA polymerase synthesizes a complementary strand of DNA by adding nucleotides to the growing strand.


7. In the DNA replication process, the lagging strand is synthesized in:

  • A) A continuous manner
  • B) A discontinuous manner
  • C) A reverse manner
  • D) A straight-line manner

Answer: B
Explanation: The lagging strand is synthesized in a discontinuous manner because it is oriented in the opposite direction to the replication fork.


8. What is the role of RNA primer in DNA replication?

  • A) To initiate the replication process
  • B) To provide energy for replication
  • C) To join Okazaki fragments
  • D) To unwind the DNA

Answer: A
Explanation: The RNA primer provides a starting point for DNA polymerase to begin DNA synthesis.


9. What is the significance of the central dogma of molecular biology?

  • A) It explains the flow of genetic information
  • B) It explains the structure of DNA
  • C) It defines the process of protein folding
  • D) It explains how genes are inherited

Answer: A
Explanation: The central dogma explains the flow of genetic information from DNA to RNA to protein.


10. Which of the following processes converts DNA into RNA?

  • A) Replication
  • B) Transcription
  • C) Translation
  • D) Mutation

Answer: B
Explanation: Transcription is the process by which DNA is transcribed into RNA.


11. Which of the following is the function of ribosomes during translation?

  • A) To synthesize DNA
  • B) To attach tRNA to mRNA
  • C) To synthesize RNA
  • D) To catalyze protein synthesis

Answer: D
Explanation: Ribosomes are the site of protein synthesis and catalyze the process of translation.


12. The process of translation occurs in the:

  • A) Nucleus
  • B) Mitochondria
  • C) Ribosome
  • D) Chloroplast

Answer: C
Explanation: Translation takes place in the ribosomes, where mRNA is translated into a polypeptide chain.


13. In the genetic code, a codon consists of:

  • A) Two nucleotides
  • B) Three nucleotides
  • C) Four nucleotides
  • D) One nucleotide

Answer: B
Explanation: A codon is a sequence of three nucleotides in mRNA that codes for a specific amino acid.


14. Which of the following is an example of a point mutation?

  • A) Deletion
  • B) Substitution
  • C) Insertion
  • D) All of the above

Answer: B
Explanation: A point mutation is a mutation that affects a single nucleotide base, such as a substitution.


15. What is the function of the 5' cap added to mRNA?

  • A) To protect the mRNA from degradation
  • B) To help mRNA bind to the ribosome
  • C) To initiate transcription
  • D) To allow mRNA to exit the nucleus

Answer: A
Explanation: The 5' cap protects mRNA from degradation and helps in ribosome binding during translation.


16. Which of the following is the process of protein synthesis from mRNA?

  • A) Replication
  • B) Translation
  • C) Transcription
  • D) Replication and transcription

Answer: B
Explanation: Translation is the process where mRNA is used as a template to synthesize proteins.


17. Which type of RNA carries the genetic information from DNA to the ribosome?

  • A) tRNA
  • B) rRNA
  • C) mRNA
  • D) hnRNA

Answer: C
Explanation: mRNA (messenger RNA) carries the genetic information from the DNA to the ribosomes for protein synthesis.


18. Which of the following is true about tRNA?

  • A) It carries the amino acid to the ribosome
  • B) It carries the genetic code to the ribosome
  • C) It is synthesized in the nucleus
  • D) It directly codes for protein synthesis

Answer: A
Explanation: tRNA (transfer RNA) carries amino acids to the ribosome during translation.


19. What is the name of the process by which a cell divides to form gametes?

  • A) Mitosis
  • B) Meiosis
  • C) Binary fission
  • D) Cytokinesis

Answer: B
Explanation: Meiosis is the process by which a diploid cell divides to form haploid gametes (sperm and egg).


20. What is the role of the operator in an operon?

  • A) To bind RNA polymerase
  • B) To bind repressor proteins
  • C) To synthesize proteins
  • D) To produce mRNA

Answer: B
Explanation: The operator is a sequence of DNA that binds repressor proteins, which can block the transcription of genes in the operon.


21. Which of the following is the function of the promoter region in an operon?

  • A) To prevent the binding of RNA polymerase
  • B) To synthesize RNA
  • C) To bind RNA polymerase and initiate transcription
  • D) To regulate gene expression

Answer: C
Explanation: The promoter region is where RNA polymerase binds to initiate transcription.


22. Which enzyme is responsible for joining the Okazaki fragments on the lagging strand during DNA replication?

  • A) Helicase
  • B) Ligase
  • C) DNA polymerase
  • D) Primase

Answer: B
Explanation: Ligase joins the Okazaki fragments on the lagging strand by forming phosphodiester bonds between them.


23. The process of gene expression involves which of the following steps?

  • A) Transcription and translation
  • B) Replication and transcription
  • C) Replication and translation
  • D) Mutation and translation

Answer: A
Explanation: Gene expression involves transcription (DNA to RNA) followed by translation (RNA to protein).


24. Which of the following is true about the structure of RNA?

  • A) RNA is double-stranded
  • B) RNA contains the base thymine
  • C) RNA contains the sugar ribose
  • D) RNA is not involved in protein synthesis

Answer: C
Explanation: RNA contains the sugar ribose, unlike DNA, which contains deoxyribose.


25. Which of the following mutations results in a change in the amino acid sequence of a protein?

  • A) Silent mutation
  • B) Missense mutation
  • C) Nonsense mutation
  • D) Frameshift mutation

Answer: B
Explanation: A missense mutation results in the substitution of one amino acid for another in the protein sequence.


26. What is the main function of the exon regions of a gene?

  • A) To code for non-coding proteins
  • B) To be spliced out during RNA processing
  • C) To code for the protein sequence
  • D) To regulate gene expression

Answer: C
Explanation: Exons are the coding regions of a gene that are spliced together to form mature mRNA.


27. The process of DNA replication is said to be:

  • A) Conservative
  • B) Semiconservative
  • C) Dispersive
  • D) Non-conservative

Answer: B
Explanation: DNA replication is semiconservative, meaning each new DNA molecule contains one old strand and one new strand.


28. The genetic code is said to be:

  • A) Ambiguous
  • B) Universal
  • C) Specific to prokaryotes
  • D) Specific to eukaryotes

Answer: B
Explanation: The genetic code is universal, meaning it is the same for almost all organisms.


29. Which of the following is the correct order of events in translation?

  • A) Elongation → Initiation → Termination
  • B) Initiation → Elongation → Termination
  • C) Initiation → Termination → Elongation
  • D) Elongation → Termination → Initiation

Answer: B
Explanation: The correct order of events in translation is initiation, elongation, and termination.


30. Which of the following is a function of the 3' poly-A tail added to mRNA?

  • A) To protect mRNA from degradation
  • B) To initiate transcription
  • C) To help in ribosome binding
  • D) To prevent the formation of introns

Answer: A
Explanation: The poly-A tail protects mRNA from degradation and aids in the export of mRNA from the nucleus.


31. Which of the following processes occurs first during the central dogma?

  • A) Translation
  • B) Replication
  • C) Transcription
  • D) Mutation

Answer: C
Explanation: Transcription occurs first as the DNA is transcribed into mRNA before translation occurs in the cytoplasm.


32. What is the function of the lac operon in bacteria?

  • A) To replicate the DNA
  • B) To digest lactose
  • C) To repair DNA
  • D) To synthesize RNA

Answer: B
Explanation: The lac operon regulates the breakdown of lactose in bacteria. It controls the expression of genes that help digest lactose when it is available.


33. What is the function of the DNA ligase enzyme?

  • A) To unwind the DNA
  • B) To join Okazaki fragments
  • C) To add nucleotides to the growing strand
  • D) To initiate transcription

Answer: B
Explanation: DNA ligase is responsible for joining the Okazaki fragments on the lagging strand during DNA replication.


34. What is the first step in the process of translation?

  • A) Binding of mRNA to the ribosome
  • B) Binding of tRNA to mRNA
  • C) Formation of peptide bonds
  • D) Formation of the transcription complex

Answer: A
Explanation: The first step in translation is the binding of mRNA to the ribosome.


35. Which enzyme is responsible for synthesizing the RNA strand during transcription?

  • A) RNA polymerase
  • B) DNA polymerase
  • C) Ligase
  • D) Helicase

Answer: A
Explanation: RNA polymerase is responsible for synthesizing RNA from a DNA template during transcription.


36. Which of the following is the most common type of mutation?

  • A) Point mutation
  • B) Chromosomal mutation
  • C) Insertion mutation
  • D) Deletion mutation

Answer: A
Explanation: Point mutations, which involve a change in a single nucleotide, are the most common type of mutation.


37. Which of the following is a characteristic of a virus?

  • A) It is made of proteins only
  • B) It can replicate independently
  • C) It contains DNA or RNA but not both
  • D) It contains ribosomes

Answer: C
Explanation: Viruses contain either DNA or RNA, but not both, and they cannot replicate independently without a host cell.


38. Which of the following is NOT true about RNA processing?

  • A) Introns are spliced out
  • B) Exons are joined together
  • C) A 5' cap is added to the RNA
  • D) A poly-A tail is removed

Answer: D
Explanation: The poly-A tail is added to RNA during processing, not removed.


39. What does the process of DNA transcription result in?

  • A) mRNA
  • B) tRNA
  • C) Protein
  • D) Ribosomal RNA

Answer: A
Explanation: Transcription results in the formation of mRNA, which carries the genetic code from the DNA to the ribosomes.


40. What is the function of the sigma factor in prokaryotic transcription?

  • A) To promote RNA synthesis
  • B) To initiate the binding of RNA polymerase to DNA
  • C) To remove introns
  • D) To add a 5' cap

Answer: B
Explanation: The sigma factor helps RNA polymerase bind to the promoter region to initiate transcription in prokaryotes.


41. What is the end product of the process of transcription?

  • A) Protein
  • B) DNA
  • C) mRNA
  • D) rRNA

Answer: C
Explanation: The end product of transcription is mRNA, which is used as a template for protein synthesis in translation.


42. Which of the following enzymes is involved in proofreading DNA during replication?

  • A) DNA polymerase
  • B) RNA polymerase
  • C) Ligase
  • D) Topoisomerase

Answer: A
Explanation: DNA polymerase has proofreading activity and ensures that the newly synthesized DNA strand is correct.


43. Which type of RNA is involved in the regulation of gene expression and plays a role in RNA interference?

  • A) mRNA
  • B) rRNA
  • C) tRNA
  • D) miRNA

Answer: D
Explanation: miRNA (microRNA) regulates gene expression by binding to mRNA and preventing its translation.


44. What does the term 'genetic code' refer to?

  • A) The sequence of amino acids in a protein
  • B) The sequence of nucleotides in RNA
  • C) The sequence of nucleotides in DNA that codes for proteins
  • D) The sequence of nucleotides in DNA that does not code for proteins

Answer: C
Explanation: The genetic code refers to the sequence of nucleotides in DNA that codes for proteins.


45. What is the difference between prokaryotic and eukaryotic transcription?

  • A) Prokaryotes do not have RNA polymerase
  • B) Eukaryotes have a nucleus where transcription occurs
  • C) Prokaryotes do not have introns
  • D) Eukaryotes do not have a genetic code

Answer: B
Explanation: In eukaryotes, transcription occurs in the nucleus, whereas in prokaryotes, it occurs in the cytoplasm.


46. Which of the following does NOT occur in the process of DNA replication?

  • A) Formation of the replication bubble
  • B) Synthesis of RNA primers
  • C) Unwinding of DNA by helicase
  • D) Formation of the mRNA strand

Answer: D
Explanation: mRNA is not formed during DNA replication; it is synthesized during transcription.


47. Which of the following is TRUE about the genetic material in viruses?

  • A) It is always DNA
  • B) It can be either DNA or RNA
  • C) It is never single-stranded
  • D) It is always double-stranded

Answer: B
Explanation: Viruses can have either DNA or RNA as their genetic material, and it can be single or double-stranded.


48. What is the function of a promoter in a gene?

  • A) To start the process of translation
  • B) To signal the end of transcription
  • C) To help in the binding of RNA polymerase
  • D) To add a cap to the RNA molecule

Answer: C
Explanation: The promoter is a region of DNA that signals where RNA polymerase should bind to initiate transcription.


49. What is the key difference between eukaryotic and prokaryotic translation?

  • A) Eukaryotes have ribosomes in the cytoplasm, while prokaryotes do not
  • B) Translation occurs in the cytoplasm in both, but in prokaryotes, it starts before transcription ends
  • C) Eukaryotes do not have ribosomes
  • D) Translation is not required in eukaryotes

Answer: B
Explanation: In prokaryotes, translation can begin before transcription is complete, while in eukaryotes, transcription and translation are separate processes.


50. Which of the following is NOT true about eukaryotic gene expression?

  • A) It involves the removal of introns
  • B) It includes the formation of mRNA
  • C) It involves the use of ribosomes in the cytoplasm
  • D) It requires RNA polymerase II for transcription

Answer: C
Explanation: Ribosomes are involved in translation, not gene expression itself. Gene expression includes processes like transcription and RNA processing.