Selected MCQ

Current Question
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 1
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 2
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 3
A point mutation changes a codon for an amino acid to a stop codon. This is called a:
  • A. Missense mutation
  • B. Silent mutation
  • C. Nonsense mutation
  • D. Frameshift mutation
Correct Answer: C
Explanation:
Changing an amino acid codon to a stop codon prematurely terminates translation, producing a truncated protein; this is a nonsense mutation.
Related Question 4
DNA methylation at CpG islands in gene promoters typically leads to:
  • A. Transcriptional activation
  • B. Transcriptional silencing
  • C. Increased mutation rate
  • D. Immediate DNA repair
Correct Answer: B
Explanation:
Methylation of cytosines in promoters condenses chromatin and represses transcription, silencing the gene.
Related Question 5
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.