NEET UG - Gene expression and regulation - operon concept, mutations, DNA repair Online Test (MCQ Quiz)

1. What is an operon?

A) A single gene that codes for a protein. B) A cluster of genes transcribed together under the control of a single promoter. C) A regulatory protein that binds to DNA. D) A type of RNA molecule involved in protein synthesis.

2. In the lac operon model of E. coli, what molecule acts as the inducer?

A) Lactose B) Allolactose C) Repressor protein D) Beta-galactosidase

3. Which gene in the lac operon codes for the enzyme that hydrolyzes lactose into glucose and galactose?

A) lacZ B) lacY C) lacA D) lacI

4. What is the function of the lacI gene in the lac operon?

A) Codes for beta-galactosidase. B) Codes for permease. C) Codes for the repressor protein. D) Codes for transacetylase.

5. Under conditions of high glucose levels in E. coli, what is the effect on the lac operon's transcription?

A) Transcription is maximally activated. B) Transcription is repressed. C) Transcription is induced by lactose. D) Transcription is slightly reduced due to catabolite repression.

6. What is catabolite repression in the context of the lac operon?

A) The repression of the lac operon by the presence of lactose. B) The activation of the lac operon by the absence of glucose. C) The repression of the lac operon by high levels of glucose. D) The induction of the lac operon by the repressor protein.

7. What is the role of CAP (Catabolite Activator Protein) in the lac operon?

A) It binds to the operator and blocks transcription. B) It binds to the promoter and enhances transcription in the absence of glucose. C) It is synthesized in the presence of lactose to induce the operon. D) It degrades lactose into simpler sugars.

8. In the trp operon of E. coli, what molecule acts as the corepressor?

A) Tryptophan B) Repressor protein C) ATP D) RNA polymerase

9. When tryptophan levels are high in E. coli, what is the state of the trp operon?

A) It is fully transcribed. B) It is repressed. C) It is induced. D) It is partially transcribed.

10. Which component of the trp operon binds to the operator to block transcription when tryptophan is present?

A) Trp repressor complex B) RNA polymerase C) Promoter D) Leader sequence

11. What is a mutation?

A) A process of DNA replication. B) A permanent alteration in the DNA sequence. C) The synthesis of proteins from mRNA. D) The regulation of gene expression.

12. Which type of mutation involves the substitution of a single nucleotide base?

A) Insertion B) Deletion C) Point mutation D) Frameshift mutation

13. A mutation that changes a codon to a stop codon is called a:

A) Silent mutation B) Missense mutation C) Nonsense mutation D) Neutral mutation

14. A mutation where a single nucleotide is replaced by another, resulting in a different amino acid, is known as a:

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

15. Which type of mutation results in a shift in the reading frame of the mRNA sequence?

A) Point mutation B) Substitution C) Insertion or deletion of nucleotides (not in multiples of three) D) Silent mutation

16. What is a silent mutation?

A) A mutation that results in cell death. B) A mutation that changes an amino acid to a stop codon. C) A mutation that alters a codon but does not change the encoded amino acid. D) A mutation that causes a frameshift.

17. Which of the following is a common mutagen?

A) Oxygen B) Ultraviolet (UV) radiation C) Water D) Carbon dioxide

18. What is the primary function of DNA repair mechanisms?

A) To increase the rate of mutations. B) To correct errors introduced during DNA replication or damage to DNA. C) To synthesize new DNA strands. D) To regulate gene expression.

19. Which DNA repair pathway involves the removal of a damaged nucleotide and its replacement with a correct one?

A) Mismatch repair B) Nucleotide excision repair (NER) C) Base excision repair (BER) D) Direct repair

20. The mismatch repair system primarily corrects:

A) UV-induced pyrimidine dimers. B) Errors in base pairing that escape proofreading during replication. C) Bulky DNA adducts. D) Oxidized bases.

21. Nucleotide Excision Repair (NER) is particularly effective at repairing:

A) Single base mismatches. B) Depurination. C) Bulky lesions like thymine dimers caused by UV radiation. D) Deamination of cytosine.

22. What is the role of the repressor protein in a repressible operon, like the trp operon?

A) It binds to the promoter to activate transcription. B) It binds to the operator to block transcription when the end product is abundant. C) It acts as an inducer to start transcription. D) It is always bound to the operator, preventing transcription.

23. In the lac operon, the promoter is the site where:

A) The repressor protein binds. B) RNA polymerase binds to initiate transcription. C) The inducer molecule binds. D) The operator sequence is located.

24. What happens to the lac operon when lactose is present and glucose is absent?

A) The operon is repressed. B) The operon is induced and CAP is bound, leading to high transcription. C) Transcription is blocked by the repressor. D) CAP cannot bind, so transcription is low.

25. A mutation that results in a codon specifying a different amino acid is a:

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

26. Which type of mutation is caused by the insertion or deletion of nucleotides in a number not divisible by three?

A) Point mutation B) Substitution C) Frameshift mutation D) Silent mutation

27. What is the function of the operator in an operon?

A) It is a binding site for RNA polymerase. B) It is a binding site for the repressor protein or activator protein. C) It codes for structural genes. D) It is a regulatory gene.

28. In the trp operon, when tryptophan levels are low, the repressor protein is:

A) Active and bound to the operator. B) Inactive and not bound to the operator, allowing transcription. C) Degraded by the cell. D) Bound to tryptophan, making it active.

29. Which enzyme is encoded by the lacZ gene in the lac operon?

A) Permease B) Transacetylase C) Beta-galactosidase D) Repressor protein

30. What is the role of permease (encoded by lacY) in the lac operon?

A) To break down lactose. B) To transport lactose into the cell. C) To modify lactose. D) To block transcription.

31. Direct repair of DNA damage involves:

A) Removal of a damaged nucleotide. B) Enzymatic reversal of DNA damage, like photoreactivation of pyrimidine dimers. C) Resynthesis of a DNA segment. D) Mismatch correction.

32. Which DNA repair mechanism is responsible for fixing depurination or deamination errors?

A) Nucleotide Excision Repair B) Mismatch Repair C) Base Excision Repair D) Photoreactivation

33. What is the primary consequence of a frameshift mutation?

A) A single amino acid change. B) No change in the amino acid sequence. C) A complete alteration of the amino acid sequence downstream of the mutation. D) Formation of a stop codon.

34. In the absence of lactose, the lac repressor protein is:

A) Inactive and cannot bind to the operator. B) Active and binds to the operator, blocking transcription. C) Degraded by the cell. D) Bound to cAMP.

35. The structural genes of the lac operon are transcribed as a single polycistronic mRNA because they are under the control of:

A) Multiple promoters B) A single promoter C) The operator region D) The repressor protein

36. Which of the following is an example of a constitutive gene in the context of the lac operon?

A) lacZ B) lacY C) lacI D) None of the above

37. What is the function of transacetylase (encoded by lacA) in the lac operon?

A) To transport lactose. B) To hydrolyze lactose. C) To acetylate thiogalactosides, a detoxification function. D) To regulate the operon.

38. A mutation that converts a codon for an amino acid into a stop codon is called a:

A) Missense mutation B) Silent mutation C) Nonsense mutation D) Neutral mutation

39. Which type of DNA repair directly reverses the damage without removing any nucleotides?

A) Base Excision Repair B) Nucleotide Excision Repair C) Mismatch Repair D) Direct Reversal Repair

40. What is the effect of high glucose concentration on CAP binding to the promoter of the lac operon?

A) CAP binds strongly, activating transcription. B) CAP binds weakly or not at all, reducing activation. C) CAP is degraded. D) CAP binds to the operator instead of the promoter.

41. The trp operon is an example of:

A) An inducible operon B) A constitutive operon C) A repressible operon D) A simple gene system

42. What is the function of the leader sequence (trpL) in the trp operon?

A) It encodes the repressor protein. B) It contains the operator sequence. C) It plays a role in attenuation, regulating transcription termination. D) It is the promoter region.

43. A mutation that changes a codon so that it still codes for the same amino acid is known as a:

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

44. Which of the following is a type of spontaneous mutation?

A) Mutation induced by UV radiation B) Mutation induced by chemical mutagens C) Tautomeric shift of bases D) Mutation induced by X-rays

45. The enzyme that fixes UV-induced pyrimidine dimers in E. coli is part of:

A) Base Excision Repair B) Mismatch Repair C) Nucleotide Excision Repair D) Direct Repair (photolyase)

46. What is the primary role of cyclic AMP (cAMP) in the regulation of the lac operon?

A) It binds to the repressor protein, inactivating it. B) It binds to CAP, forming a complex that binds to the promoter. C) It directly induces the transcription of lacZ. D) It inhibits the synthesis of beta-galactosidase.

47. Which of the following is NOT a structural gene in the lac operon?

A) lacZ B) lacY C) lacA D) lacI

48. In the context of operons, what does 'polycistronic mRNA' refer to?

A) An mRNA molecule that codes for only one protein. B) An mRNA molecule that codes for multiple proteins from a single transcript. C) An mRNA molecule that is transcribed from a single gene. D) An mRNA molecule that is highly regulated.

49. What is the consequence of a deletion of the operator region in the lac operon?

A) The operon will always be repressed. B) The operon will always be induced, regardless of lactose presence. C) Transcription will be significantly reduced. D) The repressor protein will bind more strongly.

50. Which repair mechanism is crucial for maintaining the fidelity of DNA replication by correcting mispaired bases after replication has occurred?

A) Nucleotide Excision Repair B) Base Excision Repair C) Mismatch Repair D) Direct Repair

Gene expression and regulation - operon concept, mutations, DNA repair - Online Test

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