Selected MCQ

Current Question
The smooth endoplasmic reticulum (SER) is primarily involved in which of the following cellular functions?
  • A. Synthesis of secretory and membrane proteins
  • B. Detoxification of xenobiotics and synthesis of lipids
  • C. ATP production via oxidative phosphorylation
  • D. Packaging and modification of proteins in vesicles
Correct Answer: B
Explanation:
The smooth ER specializes in lipid and steroid synthesis, as well as the detoxification of drugs and other harmful compounds. (Protein synthesis occurs on the rough ER; packaging occurs in the Golgi.)
Related Question 1
Small interfering RNAs (siRNAs) are primarily involved in which cellular process?
  • A. DNA replication
  • B. RNA interference (RNAi) leading to mRNA degradation
  • C. Protein synthesis
  • D. Glycolysis
Correct Answer: B
Explanation:
siRNAs guide the RNA-induced silencing complex (RISC) to complementary mRNA, causing its cleavage and degradation, a form of RNA interference.
Related Question 2
Which of the following events in protein targeting to the endoplasmic reticulum is directly mediated by the signal recognition particle (SRP)?
  • A. Cleavage of the signal peptide after translocation
  • B. Pausing of translation until the ribosome binds the ER
  • C. Glycosylation of the protein in the ER lumen
  • D. Folding of the protein by lumenal chaperones
Correct Answer: B
Explanation:
The SRP binds the signal peptide and ribosome, pausing translation until the complex docks on the SRP receptor on the ER membrane.
Related Question 3
Which organelle contains hydrolytic enzymes and is involved in the degradation of cellular components during autophagy?
  • A. Lysosome
  • B. Proteasome
  • C. Golgi apparatus
  • D. Smooth endoplasmic reticulum
Correct Answer: A
Explanation:
Lysosomes contain acid hydrolases that fuse with autophagosomes to degrade cellular organelles and proteins.
Related Question 4
Histone H1 differs from the core histones (H2A, H2B, H3, H4) because it primarily functions to:
  • A. Form the core nucleosome octamer
  • B. Bind linker DNA between nucleosomes
  • C. Methylate DNA
  • D. Act as a transcription factor
Correct Answer: B
Explanation:
Histone H1 binds to the linker DNA between nucleosomes, helping to compact chromatin into higher-order structures.
Related Question 5
The signal recognition particle (SRP) functions primarily to:
  • A. Direct ribosomes to the rough ER membrane for secretory proteins
  • B. Unfold misfolded proteins in the cytosol
  • C. Bind and degrade abnormal mRNA
  • D. Stimulate nuclear export of ribosomal subunits
Correct Answer: A
Explanation:
SRP binds the signal peptide of a nascent polypeptide and pauses translation until the ribosome docks on the ER, targeting the protein to the secretory pathway.