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Cell Communication
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Chapter 11
Communication Methods
 Cell-to-cell contact
 Local signaling
 Long distance signaling
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Cell-to-Cell Communications
 Cell junctions directly connect the

cytoplasm of adjacent cells
 Ex: cardiac cells for rhythmicity;
plamodesmata between plant cells
Surface receptors can give/send
information

Ex: specific immune response
Plasma membranes
Gap junctions
between animal cells
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Plasmodesmata
between plant cells
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Local Signaling

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Adjacent cells are signaled.

Chemical messengers released
 Ex: Neurotransmitters via neurons
Local signaling
Target cell
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Local regulator
diffuses through
extracellular fluid
(a) Paracrine signaling. A secreting cell acts
on nearby target cells by discharging
molecules of a local regulator (a growth
factor, for example) into the extracellular
fluid.
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Target cell
is stimulated
(b) Synaptic signaling. A nerve cell
releases neurotransmitter molecules
into a synapse, stimulating the
target cell.
Yeast Sexual Reproduction
1
Yeast cells identify
their mates by
local cell
signaling.
2
3
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Exchange of
mating factors.
Each cell type
secretes a
mating factor
that binds to
receptors on
the other cell
type.
Mating. Binding
of the factors to
receptors
induces changes
in the cells that
lead to their
fusion.
New a/ cell.
The nucleus of
the fused cell
includes all the
genes from the
a and a cells.
 factor
Receptor
a

Yeast cell,
mating type a
 factor
Yeast cell,
mating type 

a
a/
Long Distance Signaling
 Use of
hormones
 Can affect many
cells
 Protein or
Steroid types
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Signal Transduction Pathways
 Convert signals on
a cell’s surface
into cellular
responses
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3 Phases of Signal Transduction
EXTRACELLULAR
FLUID
1 Reception
Plasma membrane
CYTOPLASM
2 Transduction
3 Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction pathway
Signal
molecule
Figure 11.5
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Step One - Reception
 Reception occurs when a signal molecule
(ligand) binds to a receptor protein.
 Ligand and receptor have a unique bonding
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Step Two - Transduction
 Signal initiated by conformational change
of receptor protein
 Signal is turned into a cellular response.

cascades relay signals to target

second messengers involved
 Multistep pathways can amplify a signal
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 Transduction by a phosphorylation cascade
Signal molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
1 A relay molecule
activates protein kinase 1.
2 Active protein kinase 1
transfers a phosphate from ATP
to an inactive molecule of
protein kinase 2, thus activating
this second kinase.
Active
protein
kinase
1
Inactive
protein kinase
2
ATP
ADP
Pi
PP
Inactive
ATP
protein kinase
ADP
3
5 Enzymes called protein
phosphatases (PP)
PP
catalyze the removal of
Pi
the phosphate groups
from the proteins,
Inactive
making them inactive
protein
and available for reuse.
Figure 11.8
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3 Active protein kinase 2
then catalyzes the phosphorylation (and activation) of
protein kinase 3.
P
Active
protein
kinase
2
Active
protein
kinase
3
P
4 Finally, active protein
kinase 3 phosphorylates a
protein (pink) that brings
about the cell’s response to
the signal.
ATP
P
ADP
Pi
PP
Active
protein
Cellular
response
Benefits of a 2° messenger system
signal
1
Activated adenylyl cyclase
receptor protein
2
Not yet
activated
amplification
4
3
GTP
amplification
cAMP
amplification
5
G protein
protein kinase
6
amplification
Amplification!
enzyme
Cascade multiplier!
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FAST
7
amplification
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product
Step Three - Response
 Cell signaling leads to regulation of
cytoplasmic activities or gene
expression
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Regulating Gene Expression
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Types of Receptors
 There are three main types of
plasma membrane receptors:
 G-protein-linked
 Tyrosine kinases
 Ion channel
 Intracellular
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G-protein-linked receptors
 Very common
 Results in a single pathway response
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Receptor tyrosine kinases
 Multiple pathway response
Signal-binding site
Signal
molecule
Helix in the
Membrane
Signal
molecule
Tyrosines
Tyr
Tyr
Tyr
CYTOPLASM
Receptor tyrosine
kinase proteins
(inactive monomers)
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Dimer
Figure 11.7
Activated
relay proteins
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
6
ATP
Activated tyrosinekinase regions
(unphosphorylated
dimer)
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6 ADP
P Tyr
P Tyr
P Tyr
Tyr P
Tyr P
Tyr P
Fully activated receptor
tyrosine-kinase
(phosphorylated
dimer)
P Tyr
P Tyr
P Tyr
Tyr P
Tyr P
Tyr P
Inactive
relay proteins
Cellular
response 1
Cellular
response 2
Ion Channel Receptors
• When ligand binds, channel can open or close.
Ex: neurotransmitters bind as ligands for Na+ ion channels
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Intracellular Receptors
 Target protein is INSIDE the cell
 Must be hydrophobic molecule
Hormone
EXTRACELLULAR
(testosterone)
FLUID
Why can the
signal molecule
meet its target
INSIDE the cell?
Receptor
protein
Plasma
membrane
Hormonereceptor
complex
2 Testosterone binds
to a receptor protein
in the cytoplasm,
activating it.
NUCLEUS
CYTOPLASM
receptor complex
enters the nucleus
and binds to specific
genes.
4
mRNA
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hormone testosterone
passes through the
plasma membrane.
3 The hormone-
DNA
Figure 11.6
1 The steroid
New protein
The bound protein
stimulates the
transcription of
the gene into mRNA.
5 The mRNA is
translated into a
specific protein.
Evolutionary Significance
 Unicellular and multicellular cell
communication have similarities
 Highly conserved mechanisms
 Bacteria secrete molecules to sense
density of own population.

Quorum Sensing
TEDED Quorum Sensing
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