Mechanism of Hormone Action MCQ - Practice Questions with Answers

• The hormones can be of two types:
  • Water-soluble, such as amino acid derivatives, peptide hormones and protein hormones
  • Lipid soluble, such as steroid hormones
• The water-soluble hormones need an extracellular receptor and a secondary messenger for carrying out their activity.
• Lipid soluble hormones can act directly on the DNA.

Mode of Protein Hormone Action through Extracellular Receptors:

• Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
• The hormone-receptor complex induces the release of GDP from the G protein.
• The α- subunit bearing GTP separates from the combined β and у subunits. The β and у subunits do not separate from each other. 
• The activated β and γ subunits of G protein activate adenyl cyclase. 
• The activated adenyl cyclase catalyses the formation of cyclic adenosine monophosphate (cAMP) from ATP.
• The hormone is called the first messenger and cAMP is termed the second messenger.
• Amplification of the signal through a cascade effect.

Mode of Steroid Hormone Action through Intracellular Receptors:

• Steroid hormones are lipid-soluble and easily pass through the cell membrane of a target cell into the cytoplasm. 
• In the cytoplasm, they bind to specific intracellular receptors (proteins) to form a hormone-receptor complex that enters the nucleus.
• In the nucleus, they regulate gene expression or chromosome function.