Transcript Lecture # 5 Date

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Chapter 11 – Cell
Communication
Signal-transduction pathway
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Signal on a cell’s surface is converted into a specific cellular response
Local signaling (short distance):
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Paracrine (growth factors)
Synaptic (neurotransmitters)
Long distance: hormones
Signal Transduction Pathway
Cell Signaling
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Reception – target cell detection of a signal molecule, is detected
when signal molecule binds to receptors surface
Transduction – converts the signal to a form that can bring about a
cellular response; can be a single-step or a series of changes
(signal transduction pathway)
Response – triggering of a specific cellular response
Cell Signalling
Membrane Receptors
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G-protein linked
receptors
GDP bound =
inactive
GTP bound = active
Receptor is active
when signal is
attached
Enzyme activated,
GTP  GDP
Membrane Receptors
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Tyrosine kinases
Kinases –
phosphorylate
Can trigger multiple
cellular responses
Signal binding
causes dimer
formation
Adds phosphates
Activates relay
proteins to elicit
cellular response
Membrane
Receptors
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Ion channel receptors
When signal is absent,
gate closed
Signal (ligand) binds –
gate opens, ions move in,
elicit cellular response
Signal detaches closing
the gate
Transduction Pathways
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Phosphorylation
cascade
Adding P from
ATP to activate
proteins
Uses protein
kinases
Approx. 2% of
our genes
thought to code
for protein
kinases
Transduction Pathways
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Second messengers
Non-protein pathways
Example – cAMP (cyclic
adenosine
monophosphate)
Includes a g-proteinlinked receptor
The cAMP activates
another protein (usually
kinase)
Animation
Response
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Cytoplasmic response
Regulate the activity
of enzymes
Example breakdown
of glycogen into
glucose-1-phosphate
Also an example of
signal amplification
Animation
Response
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Nuclear response
Regulate the
synthesis of proteins
Example:
transcription factors
animation