Download The Cell Membrane

IV. Cell Signaling
Chapter 11
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External Signals are converted into
resonses within the cell
Animal cell communication
a. Direct Contact
b. Long Distance Signaling
c. Local regulators

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growth factors, neurotransmitters
Fig. 11-5
Long-distance signaling
Local signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid
(a) Paracrine signaling
Endocrine cell
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Target cell
is stimulated
Blood
vessel
Hormone travels
in bloodstream
to target cells
Target
cell
(b) Synaptic signaling
(c) Hormonal signaling
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3 Stages of cell signaling
1. Reception – binding between signal molecule
(ligand) and a receptor


Highly specific
Causes conformational change of receptor
(usually a protein)
Example: G-proteinlinked receptor works
with help of cytoplasmic G Protein.
Tyrosine kinases are then activated
and add phosphate to tyrosines on
the cytoplasmic side
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Fig. 11-7b
Plasma
membrane
G protein-coupled
receptor
Inactive
enzyme
Activated
receptor
Signaling molecule
Inactive
enzyme
GDP
CYTOPLASM
GDP
Enzyme
G protein
(inactive)
2
1
GTP
GTP replaces GDP when protein is activated by
the receptors conformational change
Activated
enzyme
Inactive
enzyme
GTP
GDP
Pi
Cellular response
3
G protein then activates an enzyme by causing
a conformational change. Enzyme can now
trigger next step in pathway
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4
G Protein hydrolyzed GTP to make GDP =
Inactive G protein and Enzyme
Example 2: Ligand gated
ion channel
 signal molecule binds to
receptor (protein
channel) and causes a
conformational change
that opens the channel
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Fig. 11-6-1
EXTRACELLULAR
FLUID
1 Reception
Receptor
Signaling
molecule
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CYTOPLASM
Plasma membrane
2. Transduction


Signal is turned into a different form
(usually, conformational change in a
protein)
Most include phosphorylation cascades
 Each molecule adding a phosphate group on to
the next molecule
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Fig. 11-6-2
CYTOPLASM
EXTRACELLULAR
FLUID
Plasma membrane
1 Reception
2 Transduction
Receptor
Relay molecules in a signal transduction pathway
Signaling
molecule
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3. regulation of

enzyme activity
 cytoskeleton rearrangement
 activate transcription factors (proteins that
turn on and off genes)
Each signal amplifies by activiting multiple
copies of the next component of the pathway.
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Fig. 11-6-3
CYTOPLASM
EXTRACELLULAR
FLUID
Plasma membrane
1 Reception
2 Transduction
3 Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction pathway
Signaling
molecule
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Fig. 11-9
Signaling molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
Active
protein
kinase
1
Inactive
protein kinase
2
ATP
ADP
Pi
P
Active
protein
kinase
2
PP
Inactive
protein kinase
3
Pi
ATP
ADP
Active
protein
kinase
3
PP
Inactive
protein
P
ATP
P
ADP
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Pi
PP
Active
protein
Cellular
response