Peptide Hormones and Steroid Hormones: Mechanisms of Action - Prof. Douglas N. Ishii, Study notes of Biology

Download Peptide Hormones and Steroid Hormones: Mechanisms of Action - Prof. Douglas N. Ishii and more Study notes Biology in PDF only on Docsity! 28 March Lipophobic ≈ hydrophilic – “like” H2O Lipophilic ≈ hydrophobic – “like” lipids Peptide Hormone – Receptor Complex Peptide hormones (H) cannot enter their target cells and must combine with membrane receptors (R) that initiate signal transduction processes Signal (peptide hormone) → receptor → intracellular signaling molecules → target protein → response Intracellular signaling molecules are amplifier enzymes or second messengers G-Protein Coupled Receptors Coupled to GTP binding protein LH, FSH, TSH receptors → cAMP GnRH receptors → IP3/Ca2+ All cross membrane 7 times Binding → conformation change → α subunit → GTP is activated → enzyme activated (e.g. adenylylcyclase, which turns ATP → cAMP) cAMP is 2nd messenger Activates protein kinase A Proteins phosphorylated Adenylylcyclase is “amplifier enzyme” – activated, then processes many molecules (not just one) cAMP – second messenger (figure 5-9) IP3 and DAG – second messenger (fig 5-10) Phospholipase C activated → PIP2 acted on → IP3 (travels to ER, ↑ Ca 2+) and DAG (activates PKC [protein kinase C]) → phosphorylates proteins → call response Ca2+ - second messenger (figure 5-11) Receptor tyrosine kinase signaling Ligand (EGF) binding and receptor aggregation → autophosphorylation of tyrosines → binding of cytosolic proteins with SH2 domains → activated PLCγ stimulates InsP3-DAG pathway → activated GRB2-Sos stimulated Ras pathway Steroid Hormones: Action Most hydrophobic steroids are bound to plasma protein carriers. Only unbound hormones can diffuse into the target cell. Steroid hormone receptors are typically in the cytoplasm or nucleus. Some steroid hormones also bind to membrane receptors that use second messenger systems to create rapid cellular responses. The receptor-hormone complex binds to DNA and activates or represses one or more genes. Activated genes create new mRNA that moves into the cytoplasm. Translation produces new proteins for cell processes. Steroid hormone receptor domains DNA binding Transactivation Hormone/ligand binding Figure 11.08 – Possible fates and actions of hormones