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IX Cell Signaling

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					           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
A.        Types of Cell
          Signaling
• Cell surface receptors vs.
  Intracellular receptors
A.       Types of Cell
         Signaling
• Three forms of signaling by secreted
  molecules
  – 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 degraded
  rapidly
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: a, b, and g
  a chain binds and hydrolyzes GTP
  b & g chains form a tight complex bg 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 a to dissociate from bg
  a 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

				
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posted:4/25/2011
language:English
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