cell signaling a.types of cell signaling b.intracellular receptor signaling: steroid hormones c.cell...
TRANSCRIPT
Cell Signaling
A. Types of Cell SignalingB. 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
A. Types of Cell Signaling
• Cell surface receptors vs. Intracellular receptors
A. Types of Cell Signaling
• Three forms of signaling by secretedmolecules– Paracrine– Synaptic– Endocrine
A. Types of Cell Signaling
• Gap junctions
A. Types of Cell Signaling
• The same signal can produce different effects in different cells
A. Types of Cell Signaling
• Proper signaling generally depends
on a signal molecule being degradedrapidly
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
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
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
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.
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
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
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
B. G-linked Receptors
• Trimeric G-proteins disassemble when activated– Three chains: and chain binds and hydrolyzes GTP & chains form a tight complex
that anchors G-protein to the plasma membrane
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 to dissociate from binds to adenylate cyclase, altering its
activity
– Gs protein stimulates activates adenylate cyclase, Gi inhibits it
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