Medicine & USMLE

Protein Hormones

Endocrine & Hormones
  1. Leptin
  2. Ghrelin
  3. Protein Hormones
  4. Steroid Hormones
  5. Insulin
  6. Diabetes
  7. Glucagon
  8. Epinephrine
  9. Cortisol
  10. Thyroid Hormones
  11. Calcitonin
  12. Parathyroid Hormone (PTH)
  13. Anterior Pituitary
  14. Prolactin
  15. Luteinizing Hormone (LH)
  16. Follicle-Stimulating Hormone (FSH)
  17. Growth Hormone (GH)
  18. Posterior Pituitary


Protein hormones, like all other proteins, are synthesized from amino acids in the rough endoplasmic reticulum. Since they have charged amino acid residues, protein hormones are hydrophilic and can thus easily dissolve in water and blood to move throughout the body. However, once a protein hormone reaches its target cell, its hydrophilic nature prevents it from directly penetrating the hydrophobic cell membrane. Instead, protein hormones bind to external receptors to initiate a secondary messenger cascade, which then alters cell function to achieve the hormone’s effects.

Key Points

  • Protein (Peptide) Hormones
    • Made of amino acids (protein)
      • Synthesized in Rough Endoplasmic Reticulum (RER)
      • Sorted and transported by Golgi Apparatus
    • Hydrophilic (water-soluble)
      • Proteins are made of charged amino acids
      • Move freely in blood
        • Because blood is mostly water
    • Cannot cross cell membrane
      • Bind to external receptors on cell surface
        • Utilize secondary messengers inside the cell