Gene expression and regulation - operon concept, mutations, DNA repair - One Line Questions

1. What is a silent mutation? — A mutation that alters a codon but does not change the encoded amino acid.
2. What is a mutation? — A permanent alteration in the DNA sequence.
3. What is the primary consequence of a frameshift mutation? — A complete alteration of the amino acid sequence downstream of the mutation.
4. What is an operon? — A cluster of genes transcribed together under the control of a single promoter.
5. In the trp operon, when tryptophan levels are low, the repressor protein is: — Inactive and not bound to the operator, allowing transcription.
6. The trp operon is an example of: — A repressible operon
7. In the context of operons, what does 'polycistronic mRNA' refer to? — An mRNA molecule that codes for multiple proteins from a single transcript.
8. Which type of DNA repair directly reverses the damage without removing any nucleotides? — Direct Reversal Repair
9. The enzyme that fixes UV-induced pyrimidine dimers in E. coli is part of: — Direct Repair (photolyase)
10. What is the effect of high glucose concentration on CAP binding to the promoter of the lac operon? — CAP binds weakly or not at all, reducing activation.
11. What is the function of the lacI gene in the lac operon? — Codes for the repressor protein.
12. In the absence of lactose, the lac repressor protein is: — Active and binds to the operator, blocking transcription.
13. Which type of mutation involves the substitution of a single nucleotide base? — Point mutation
14. What is the role of CAP (Catabolite Activator Protein) in the lac operon? — It binds to the promoter and enhances transcription in the absence of glucose.
15. What is the role of the repressor protein in a repressible operon, like the trp operon? — It binds to the operator to block transcription when the end product is abundant.
16. What is the primary role of cyclic AMP (cAMP) in the regulation of the lac operon? — It binds to CAP, forming a complex that binds to the promoter.
17. What is the function of the leader sequence (trpL) in the trp operon? — It plays a role in attenuation, regulating transcription termination.
18. What is the function of the operator in an operon? — It is a binding site for the repressor protein or activator protein.
19. When tryptophan levels are high in E. coli, what is the state of the trp operon? — It is repressed.
20. In the lac operon model of E. coli, what molecule acts as the inducer? — Allolactose
21. Which gene in the lac operon codes for the enzyme that hydrolyzes lactose into glucose and galactose? — lacZ
22. Which of the following is an example of a constitutive gene in the context of the lac operon? — lacI
23. Which of the following is NOT a structural gene in the lac operon? — lacI
24. Which DNA repair pathway involves the removal of a damaged nucleotide and its replacement with a correct one? — Base excision repair (BER)
25. A mutation that converts a codon for an amino acid into a stop codon is called a: — Nonsense mutation
26. A mutation that changes a codon so that it still codes for the same amino acid is known as a: — Silent mutation
27. The structural genes of the lac operon are transcribed as a single polycistronic mRNA because they are under the control of: — A single promoter
28. Which of the following is a type of spontaneous mutation? — Tautomeric shift of bases
29. A mutation where a single nucleotide is replaced by another, resulting in a different amino acid, is known as a: — Missense mutation
30. A mutation that results in a codon specifying a different amino acid is a: — Missense mutation
31. Which DNA repair mechanism is responsible for fixing depurination or deamination errors? — Base Excision Repair
32. Which repair mechanism is crucial for maintaining the fidelity of DNA replication by correcting mispaired bases after replication has occurred? — Mismatch Repair
33. Which of the following is a common mutagen? — Ultraviolet (UV) radiation
34. Which enzyme is encoded by the lacZ gene in the lac operon? — Beta-galactosidase
35. Which type of mutation results in a shift in the reading frame of the mRNA sequence? — Insertion or deletion of nucleotides (not in multiples of three)
36. Which type of mutation is caused by the insertion or deletion of nucleotides in a number not divisible by three? — Frameshift mutation
37. Direct repair of DNA damage involves: — Enzymatic reversal of DNA damage, like photoreactivation of pyrimidine dimers.
38. A mutation that changes a codon to a stop codon is called a: — Nonsense mutation
39. Nucleotide Excision Repair (NER) is particularly effective at repairing: — Bulky lesions like thymine dimers caused by UV radiation.
40. What happens to the lac operon when lactose is present and glucose is absent? — The operon is induced and CAP is bound, leading to high transcription.
41. What is the consequence of a deletion of the operator region in the lac operon? — The operon will always be induced, regardless of lactose presence.
42. What is catabolite repression in the context of the lac operon? — The repression of the lac operon by high levels of glucose.
43. In the lac operon, the promoter is the site where: — RNA polymerase binds to initiate transcription.
44. What is the role of permease (encoded by lacY) in the lac operon? — To transport lactose into the cell.
45. What is the primary function of DNA repair mechanisms? — To correct errors introduced during DNA replication or damage to DNA.
46. What is the function of transacetylase (encoded by lacA) in the lac operon? — To acetylate thiogalactosides, a detoxification function.
47. Under conditions of high glucose levels in E. coli, what is the effect on the lac operon's transcription? — Transcription is slightly reduced due to catabolite repression.
48. Which component of the trp operon binds to the operator to block transcription when tryptophan is present? — Trp repressor complex
49. In the trp operon of E. coli, what molecule acts as the corepressor? — Tryptophan
50. The mismatch repair system primarily corrects: — Errors in base pairing that escape proofreading during replication.
All One Line Questions
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