30.1
Signal Transduction
Purpose—regulate cellular responses to extracellular signals
Single cell organisms respond to food mostly
Glucose
Starvation
Chemotaxis
Multicellular organisms: cells must communicate with each other
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30.2
Cells communicate in different ways
Receptor types:
Steroid hormone receptors
Heterotrimeric G-protein coupled receptors
Tyrosine kinase receptors
30.3
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Heterotrimeric G
‐
protein coupled receptors
Include receptors for epinephrine, prostaglandins
~1000 different receptors in this family in humans
In the absence of hormone, heterotrimeric G protein binds GDP (inactive)
Hormone
‐
receptor complex stimulates exchange for GTP
Activates target (adenylate cyclase here) (signal amplification)
GTP slowly hydrolyzed to GDP (molecular clock) limits response
Inhibitory G proteins too that work with different receptors (integration of response to multiple
hormones)
30.4
Receptor (serpentine receptor) 7 transmembrane helices