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Cell Signaling

Cell Signaling. A. Types of Cell Signaling B. Intracellular Receptor Signaling: Steroid Hormones C. Cell Surface Receptors: Types D. Cell Surface Receptors: G-protein linked receptors. A. Types of Cell Signaling. Direct cell-cell signaling vs. signaling via secretion.

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Cell Signaling

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  1. Cell Signaling A. Types of Cell Signaling B. Intracellular Receptor Signaling: Steroid Hormones C. Cell Surface Receptors: Types D. Cell Surface Receptors: G-protein linked receptors

  2. A. Types of Cell Signaling • Direct cell-cell signaling vs.signaling via secretion

  3. A. Types of Cell Signaling • Cell surface receptors vs. Intracellular receptors

  4. A. Types of Cell Signaling • Three forms of signaling by secretedmolecules • Paracrine • Synaptic • Endocrine

  5. A. Types of Cell Signaling • Gap junctions

  6. A. Types of Cell Signaling • The same signal can produce different effects in different cells

  7. A. Types of Cell Signaling • Proper signaling generally depends on a signal molecule being degradedrapidly

  8. A. Types of Cell Signaling • Types of Signals based on Where they Bind • To an intracellular receptor: e.g. Steroid hormones • To a cell-surface receptor: G-protein linked, enzyme-linked, or ion channel-linked

  9. B. Intracellular Receptor Signaling: Steroid Hormones • Overview of Steroid Hormone Action: • Steroid hormone (small, hydrophobic) is secreted by glandular cells and released into bloodstream (usually transported via shuttle proteins) • The hormone enters the cytoplasm of cells • In the cytoplasm of target cells, the hormone binds to steroid hormone receptor protein

  10. B. Intracellular Receptor Signaling: Steroid Hormones • Overview of Steroid . . . (cont.): • The steroid-receptor conplex is translocated into the nucleus, where it activates the transcription of the primary response genes • Transcription of the primary response genes, followed by translation, results in the production of primary response proteins

  11. B. Intracellular Receptor Signaling: Steroid Hormones • Overview of Steroid . . . (cont.): • The primary response proteins usually inhibit further transcription of their own genes, and they may activate transcription of secondary response genes.

  12. C. Cell Surface Receptors: Types • Three known classes of cell surface receptors • Ion channel-linked, G-protein-linked, Enzyme-linked • An activated cell-surface receptor triggers a phosphorylation cascade

  13. D. Cell Surface Receptors: G-protein linked receptors • Largest family of cell surface receptors • Different ones respond to a wide variety of mediators including different hormones, neurotransmitters, local mediators • Examples: Receptors to epinephrine, acetylcholine, serotonin

  14. B. G-linked Receptors • What do G-protein receptors do? • G-protein receptors activate trimeric G-protein • Activated G-protein alters the cellular concentration of a “second messenger”: usually cyclic AMP or Ca2+ • The second messenger activates a protein kinase enzyme • The protein kinase phosphorylates another enzyme and alters its activity

  15. B. G-linked Receptors • Trimeric G-proteins disassemble when activated • Three chains: a, b, andg • a chain binds and hydrolyzes GTP • b & g chains form a tight complex bg that anchors G-protein to the plasma membrane

  16. B. G-linked Receptors • Trimeric G-proteins disassemble when activated • Inactive G-protein has a bound GDP • When activated: GDP dissociates, new GTP is bound • This causes a to dissociate from bg • a binds to adenylate cyclase, altering its activity • Gs protein stimulates activates adenylate cyclase, Gi inhibits it

  17. B. G-linked Receptors • Action of epinephrine on glycogen metabolism • Epinephrine (adrenaline) is released from the adrenal gland in times of stress. It has two overall actions on glycogen metabolism: it inhibits glycogen synthesis, and it promotes glycogen breakdown • This is mediated by a protein phosphorylation cascade

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