Download - Cell to Cell Communication
Cell to Cell Communication
• Signal Transduction– Converting an extracellular signal to an intracellular
response
• Primary Messengers– Hormones, neurotransmitters, growth factors,
cytokines, prostaglandins, etc.– Messenger = Ligand (Binds to receptor with great
specificity)
• Secondary Messengers– cAMP, Phosphoinositides, Ca2+
Why Use Hormone Signaling?• General systemic responses
– Any cells that possess receptors• Longer acting, slower developing responses
– Cause changes in cell growth, differentiation, function
• Exert varied responses in different cells/tissues– Cells can have different numbers of receptors or develop
different responses with same receptors
• Can integrate different messenger inputs– Control inputs can be prioritized (e.g., local control can be
modulated or overridden)
Control of Chemical Signals
• Short-term– Release, uptake and clearance
• Longer-term– Up or down regulation of number of
receptors (highly variable from ~2,000 to ~100,000)
Membrane
Hormone (H)
Receptor (R)
Extracellular
[R] + [H] [RH]
KD = [R] [H][RH]
Intracellular
[H] = KD when [R] = [RH]
What does Kd mean?
• For insulin, Kd is 2(10-8)M– M= molar = moles/liter = concentration of substance– Insulin has a molecular weight of 5,808 g/mole– Thus, concentration of insulin when half of receptors are bound
is equal to 2(10-8)M x 5,808 g/mole = 0.00012 g/l or 0.12 μg/ml
• Blood contains ~10,000 μg/ml of total protein– Insulin signaling occurs in the presence of ~100,000 excess
protein (background “noise”)
• Erythropoietin has a Kd of 10-10M (0.003 μg/ml)– Signaling occurs in the presence of >3,000,000 background