Selected MCQ

Current Question
Phospholipase C (PLC) activation results in the generation of which second messenger that releases Ca²⁺ from the endoplasmic reticulum?
  • A. cAMP
  • B. cGMP
  • C. IP₃
  • D. DAG
Correct Answer: C
Explanation:
PLC cleaves PIP₂ into IP₃ and DAG. IP₃ diffuses to the ER, causing Ca²⁺ release, while DAG activates PKC.
Related Question 1
Activation of a Gq-coupled receptor leads to which immediate change in second messenger levels?
  • A. Activation of adenylate cyclase and an increase in cAMP
  • B. Activation of phospholipase C (PLC) and increase in IP3 and DAG
  • C. Opening of potassium channels and membrane hyperpolarization
  • D. Activation of tyrosine kinase receptors and phosphorylation of STAT proteins
Correct Answer: B
Explanation:
Gq proteins activate phospholipase C, which cleaves PIP2 into IP3 and DAG. IP3 increases intracellular Ca2+, and DAG activates protein kinase C.
Related Question 2
Down syndrome (trisomy 21) results in how many total chromosomes in a karyotype?
  • A. 45
  • B. 46
  • C. 47
  • D. 48
Correct Answer: C
Explanation:
Down syndrome is caused by an extra copy of chromosome 21. Humans normally have 46 chromosomes; trisomy adds one extra, making 47.
Related Question 3
Huntington’s disease, characterized by neurodegeneration and anticipation, is inherited in which manner?
  • A. Autosomal recessive
  • B. Autosomal dominant
  • C. X-linked recessive
  • D. Mitochondrial
Correct Answer: B
Explanation:
Huntington’s disease is autosomal dominant (one mutant allele is sufficient) and shows anticipation due to CAG repeat expansion, but inheritance is strictly dominant.
Related Question 4
Activation of a Gs protein-coupled receptor typically leads to stimulation of which enzyme to increase intracellular cAMP?
  • A. Protein kinase C
  • B. Adenylyl cyclase
  • C. Phosphodiesterase
  • D. Guanylyl cyclase
Correct Answer: B
Explanation:
Gs α-subunit activates adenylyl cyclase, which converts ATP to cAMP, raising second-messenger levels.
Related Question 5
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.