Selected MCQ

Current Question
What distinguishes reverse transcription PCR (RT-PCR) from standard PCR?
  • A. Use of DNA ligase
  • B. Amplification of RNA by first creating complementary DNA
  • C. Higher temperature cycles
  • D. Use of radioactive nucleotides
Correct Answer: B
Explanation:
RT-PCR involves reverse transcription of RNA into cDNA before PCR, enabling amplification of RNA targets.
Related Question 1
Which plasmid-based technique is used to enrich and detect low-abundance mRNAs by reverse transcription into cDNA?
  • A. RFLP analysis
  • B. Northern blotting
  • C. RT-PCR (reverse-transcription PCR)
  • D. Affinity chromatography
Correct Answer: C
Explanation:
RT-PCR involves reverse-transcribing RNA to cDNA and then amplifying specific sequences by PCR. It is very sensitive for detecting low-abundance transcripts.
Related Question 2
In bacterial transcription, the σ (sigma) factor of RNA polymerase is required for:
  • A. RNA chain elongation
  • B. Recognizing promoter sequences
  • C. DNA replication
  • D. Termination of transcription
Correct Answer: B
Explanation:
The sigma subunit binds the promoter sequences (e.g., –10 and –35 regions) and directs RNA polymerase to initiate transcription at the correct site.
Related Question 3
In the *E. coli* trp operon, attenuation causes premature termination of transcription when tryptophan levels are:
  • A. High, because the ribosome does not stall on the leader peptide
  • B. Low, because the ribosome stalls on the leader peptide
  • C. High, because tryptophan activates the terminator hairpin
  • D. Low, because tryptophan activates the attenuator sequence
Correct Answer: A
Explanation:
High tryptophan allows the ribosome to quickly translate the leader peptide, enabling formation of a terminator hairpin and early transcription termination (attenuation).
Related Question 4
Histone deacetylases (HDACs) generally have what effect on gene transcription?
  • A. Increase transcription by opening chromatin
  • B. Repress transcription by condensing chromatin
  • C. Add acetyl groups to histones
  • D. Methylate DNA
Correct Answer: B
Explanation:
HDACs deacetylate histones, reducing positive charge and weakening DNA-histone interactions, thereby condensing chromatin and repressing transcription.
Related Question 5
Which of the following components is *not* required for a standard PCR reaction?
  • A. Template DNA
  • B. DNA polymerase
  • C. Primers
  • D. DNA ligase
Correct Answer: D
Explanation:
PCR requires a thermostable DNA polymerase, primers, dNTPs, and template DNA. DNA ligase is not needed because PCR does not splice DNA fragments.