Selected MCQ

Current Question
Histone acetyltransferases (HATs) play what role in transcription?
  • A. Deacetylate histones to compact chromatin
  • B. Add acetyl groups to histones, opening chromatin
  • C. Methylate DNA at promoters
  • D. Phosphorylate RNA polymerase II
Correct Answer: B
Explanation:
HATs add acetyl groups to lysine residues on histones, reducing their positive charge and loosening DNA-histone interactions, which promotes transcription.
Related Question 1
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 2
Nucleosomes are composed of DNA wrapped around an octamer of histones. How many base pairs of DNA are wrapped around one nucleosome core?
  • A. ~50 bp
  • B. ~146 bp
  • C. ~300 bp
  • D. ~10 bp
Correct Answer: B
Explanation:
About 146 base pairs of DNA wrap ~1.7 turns around the histone octamer (2 copies each of H2A, H2B, H3, H4) in a nucleosome core.
Related Question 3
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 4
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 5
In a large, randomly mating population under Hardy–Weinberg equilibrium, 9% of individuals display a recessive trait. What percentage are heterozygous carriers?
  • A. 18%
  • B. 42%
  • C. 9%
  • D. 81%
Correct Answer: B
Explanation:
If q²=0.09, then q=0.30 and p=0.70. Heterozygous frequency = 2pq = 2(0.70)(0.30) = 0.42 or 42%.