Selected MCQ

Current Question
In a kinase signaling cascade, signal amplification occurs because:
  • A. Each kinase molecule activates only one target molecule
  • B. Each activated kinase can phosphorylate and activate many target molecules
  • C. Kinases use ATP as a second messenger to spread the signal
  • D. Kinases permanently bind their substrates to propagate the signal
Correct Answer: B
Explanation:
In a cascade, each activated kinase enzyme can phosphorylate multiple downstream targets, amplifying the signal at each step.
Related Question 1
Binding of extracellular matrix protein fibronectin to a cell’s integrin receptor most directly triggers which intracellular signaling pathway?
  • A. cAMP/PKA pathway
  • B. MAP kinase (ERK) pathway
  • C. JAK/STAT pathway
  • D. Hedgehog signaling pathway
Correct Answer: B
Explanation:
Integrin activation often activates focal adhesion kinase and the MAPK/ERK cascade, promoting cell survival and proliferation.
Related Question 2
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 3
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 4
The insulin receptor has intrinsic kinase activity. Upon insulin binding, which type of residue on the receptor is autophosphorylated?
  • A. Serine
  • B. Threonine
  • C. Tyrosine
  • D. Glycine
Correct Answer: C
Explanation:
The insulin receptor is a tyrosine kinase. Upon ligand binding, it autophosphorylates tyrosine residues on its cytoplasmic domain.
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.