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BIOL1412 01 31 2014.docx

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Biological Sciences
BIOL 1412
Paul Messing

BIOL1412 01 31 2014 Topic 4: Endocrine System - regulates growth, reproduction, metabolism (long-term events) (Fig. 16.1) - glands & tissues secrete hormones which travel in blood to target cells ( = cells w/ specific receptors for that hormone) - bind to receptors + change cell activity - Receptors (proteins) found: (Fig. 16.2) (Fig. 16.3) - on cell membrane - intracellular (nuclear) - Hormone types: 1) Water Soluble Hormones: - peptides, proteins, catecholamines ( = 1st messenger) steps: a) hormone binds to cell membrane receptors b) hormone-receptor complex activates membrane proteins eg. a G-protein c) G-proteins then activates 2nd messenger systems ⇒ cAMP, Ca+2 ex. using cAMP (cyclic adenosine monophosphate) as 2nd messenger a) hormone binds to cell - surface receptor ⇒ activates a G-protein b) G-protein activates adenylate cyclase (membrane protein) c) adenylate cyclase convertsATP to cAMP ( = 2nd messenger) ∴ ⇑ [cAMP] d) cAMP ⇒ activates protein kinases (in cytosol) e) protein kinase activates other proteins (usually phosphorylates) to alter their activity ∴ changes cell activity eg. epinephrine on liver cells (activates cAMP) ⇒ causes breakdown of glycogen to glucose - released to blood Why use 2nd messenger systems? a) hormone can't enter cell (H2O soluble) b) rapid acting (enzymes already present - just activate) c) 1 hormone mol. ⇒ many enzyme mol.s activated ⇒ multiple signal d) limited - messenger broken down or removed ⇒ cAMP broken down by phosphodiesterase 2) Lipid Soluble Hormones: (Fig. 16.3) - steroid (eg. cortisol) & thyroid hormones - triggers protein synthesis - take time ∴ slow, but long lasting response - steps for action: a) Enter target cell & bind to intracellular (nuclear) receptors (in cytoplasm or nucleus) b) hormone-receptor complex binds to a specific region on DNA(activate genes)
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