chemical messengers. outline mechanisms of intercellular communication chemical messengers signal...
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Chemical messengers
Outline
• Mechanisms of intercellular communication
• Chemical messengers
• Signal transduction mechanisms
Mechanisms of intercellular communication
• Direct through gap junctions
Cells exchange chemicals through connections between cytoplasm
• Indirect through chemical messengers
The messenger must bind to a matching receptor and stimulate a response
Figure 5.1a
Indirect messengers• Autocrine: the cell secretes a
chemical which can bind on its own membrane and stimulates a response
• Paracrine: a cell secretes a chemical which can bind to a receptor on a neighboring cell trigger a response
• Hormone: a chemical travels long distance through the blood before binding to its own target organ and stimulating a response
• Neurotransmitter: influences a distant organ by secreting chemicals which travel through axons
Chemical classification of messengers
• Lipophilic molecules = lipid soluble can cross the phospholipid bilayer cannot be stored by the cell synthesized and released immediately.
ex: steroids (from cholesterol), eicosanoids (from fatty-acids)
• Lipophobic molecules = not soluble in lipid cannot cross the phospholipid bilayer can be stored in vesicles by the cell.
ex: amino acids, peptides, proteins
Transport and elimination
• For autocrines, paracrines and neurotransmitters: diffusion
• For non-water soluble hormones: transport into in the blood bound to carrier proteins for transport (steroids and thyroid hormones)
• Hormones will eventually be degraded by the liver and eliminated by the kidneys each has a characteristic ½ life.
Hormone binding• The hormones must bind
to a matching receptor
• The binding is specific for this hormone receptor affinity (a receptor might have differing affinity for various hormones (ex: epinephrine and norepinephrine)
Signal transduction: the binding of the hormone to its receptor triggers a cell response
- steroid hormone: cross the phospholipid bilayer receptors are inside the cytoplasm or nucleus activates transcription and synthesis of new proteins response slow but sustained
- Lipophobic hormones bind to receptors located on the surface of the cell membrane activates a cascade of enzymes response amplified rapid response but not sustained
Mechanisms of transduction (do not memorize these mechanisms
• The binding of the hormone to its receptor can trigger the opening of a channel, induce enzymatic activation
Application
• Cholera
Readings
• Chp. 5, p. 126-145.
• Discovery: p.128,
• Clinical connections: p. 140.
• Not expected to be known:
• Clinical connections: p. 134