Chapter 17: Endocrine System

lipid-soluble hormones

nonpolar - can go through plasma membrane; cannot dissolve in aqueous environment of blood

water-soluble hormones

polar - cannot go through plasma membrane; can dissolve in aqueous environment of blood

Describe how lipid-soluble hormones reach their target cell receptors and the type of cellular change they initiate.

travel through blood with transport protein (bound hormone) → unbound hormone moves through plasma membrane via simple diffusion → binds to intracellular hormone receptor → form hormone-receptor complex (HRC) → HRC binds to DNA sequence called hormone-response element (HRE) → mRNA synthesis → new protein (alteration in cell structure or shift in target cells’ metabolic activities)

Describe adenylate cyclase signal transduction pathway for water-soluble hormones.

first messenger hormone binds to receptor → guanine diphosphate (GDP) binds to inactive G protein → guanine triiphosphate (GTP) binds to active G protein → G protein activates adenylate cyclase → forms second messenger cAMP from ATP → cAMP activates protein kinase to phosphorylate other molecules to activate/inhibit

Describe phospholipase C signal transduction pathway for water-soluble hormones.

first messenger hormone binds to receptor → guanine diphosphate (GDP) binds to inactive G protein → guanine triiphosphate (GTP) binds to active G protein → G protein activates phospholipase C → splits PIP₂ to two secondary messengers: diaclyglycerol (DAG) and inositol triphosphate (IP₃) → DAG activates protein kinase & IP₃ increase cytosolic Ca²⁺ to activate protein kinase