Chapter 11
Cell Communication
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Cell-Cell Communication
 Animal cells use gap junctions to send
signals
Cells must be in direct contact
 Protein channels connecting two
adjoining cells

Gap junctions
between animal cells
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Cell-Cell Communication
 Plant cells use plasmodesmata to send
signals
Cells must be in direct contact
 Gaps in the cell wall connecting the two
adjoining cells together

Plasmodesmata
between plant cells
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Local Signaling
 Other types of signaling over a short
distance

Cell-cell recognition
 Membrane bound cell surface molecules
 Glycoproteins
 Glyolipids

Local regulators
 Growth factors
 Only work over a short distance
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Long-Distance Signaling
 Nervous System in Animals

Electrical signals through neurons
 Endocrine System in Animals

Uses hormones to transmit messages
over long distances
 Plants also use hormones
Some transported through vascular
system
 Others are released into the air

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Three Stages of Cell Signaling
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane
1 Reception
Receptor
The receptor and signaling molecules
fit together (lock and key model,
induced fit model, just like enzymes!)
Signaling
molecule
 Signaling molecule binds to the
receptor protein
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Three Stages of Cell Signaling
CYTOPLASM
EXTRACELLULAR
FLUID
Plasma membrane
1 Reception
2 Transduction
Receptor
2nd
Messenger!
Relay molecules in a signal transduction pathway
Signaling
molecule
 The signal is converted into a form that
can produce a cellular response
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Three Stages of Cell Signaling
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
Can be catalysis, activation of a gene,
triggering apoptosis, almost anything!
 The transduced signal triggers a
cellular response
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G-Protein Receptors
Plasma
membrane
G protein-coupled
receptor
Activated
receptor
Signaling molecule
Enzyme
GDP
2
1
CYTOPLASM
G protein
(inactive)
GDP
GTP
Activated
enzyme
i
GTP
GDP
P
4
3
Cellular response
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Inactive
enzyme
Ion Channel Receptors
 Very important in
1
Gate
closed
Ions
Signaling
molecule
(ligand)
the nervous system
 Signal triggers the
opening of an ion
channel
depolarization
 Triggered by
neurotransmitters
Ligand-gated
ion channel receptor
Plasma
membrane
2
Gate open

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Cellular
response
3
Gate closed
Fig. 11-9
Signaling molecule
Receptor
Transduction:
Activated relay
molecule
Inactive
protein kinase
1
A Phosphorylation
Cascade
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
Fig. 11-11
First messenger
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Transduction in a
G-protein pathway
Second
messenger
Protein
kinase A
Cellular responses
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Growth factor
Receptor
Response
Reception
 Many possible
outcomes
 This example
shows a
transcription
response
Phosphorylation
cascade
CYTOPLASM
Inactive
transcription
factor
Active
transcription
factor
P
DNA
Gene
NUCLEUS
mRNA
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Transduction
Response
Signaling
molecule
 Specificity of the
Receptor
signal


The same signal
molecule can
trigger different
responses
Many responses
can come from
one signal!
Relay
molecules
Response 1
Response 2
Response 3
Cell A. Pathway leads Cell B. Pathway branches,
to a single response. leading to two responses.
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 The signal
can also
trigger an
activator or
inhibitor
 The signal
can also
trigger
multiple
receptors and
different
responses
Activation
or inhibition
Response 4
Response 5
Cell C. Cross-talk occurs Cell D. Different receptor
between two pathways.
leads to a different response.
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Any Questions??
Can You Hear Me Now?
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