Selected MCQ

Current Question
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 1
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 2
In the lac operon of *E. coli*, if both lactose and glucose are abundant in the medium, what is the expected effect on lac operon transcription?
  • A. High transcription of lac genes
  • B. Low transcription due to catabolite repression
  • C. No transcription at all
  • D. On only if allolactose is present
Correct Answer: B
Explanation:
High glucose lowers cAMP levels, so CAP is inactive. Even with lactose present (inactivating the repressor), transcription is reduced (catabolite repression).
Related Question 3
Which motor protein transports vesicles toward the plus end of microtubules (generally the cell periphery)?
  • A. Kinesin
  • B. Dynein
  • C. Myosin
  • D. Actin
Correct Answer: A
Explanation:
Kinesin moves cargo anterogradely toward microtubule plus ends (cell periphery). Dynein moves cargo retrogradely (toward minus ends).
Related Question 4
Alternative splicing occurs during gene expression at the level of:
  • A. DNA replication
  • B. Transcription initiation
  • C. Pre-mRNA processing (RNA splicing)
  • D. Protein folding
Correct Answer: C
Explanation:
Alternative splicing of pre-mRNA allows different exons to be joined or skipped, producing multiple mRNA variants from one gene during RNA processing.
Related Question 5
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.