Transcript video slide - Mrs. Felker`s Science Site

Cell Communication
AP Biology
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 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
Long-distance signaling
Endocrine cell
 Use of hormones
Both plants and animals
use hormones (e.g. Insulin)
Can affect many cells in
other parts of the body
Blood
vessel


Hormone travels
in bloodstream
to target cells
 Two types of hormones


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Protein
Steroid
Target
cell
Figure 11.4 C
(c) Hormonal signaling. Specialized
endocrine cells secrete hormones
into body fluids, often the blood.
Hormones may reach virtually all
body cells.
How Does it Work?
 Signal Transduction Pathways
 Convert signals on a cell’s surface
into cellular responses
 Are similar in microbes and
mammals, suggesting an early origin
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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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Where else have we seen two molecules with a unique
bond?
Types of Receptors
 There are three main types of
plasma membrane receptors:
 G-protein-linked
 Tyrosine kinases
 Ion channel
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G-protein-linked receptors
 Very common
 Results in a single pathway response
G-protein-linked
Receptor
Plasma Membrane
GDP
CYTOPLASM
G-protein
(inactive)
Enzyme
Activated
Receptor
GDP
Inactivate
enzyme
Signal molecule
GTP
Activated
enzyme
GTP
GDP
Pi
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Cellular response
Receptor tyrosine kinases
 Multiple pathway response
Signal-binding site
Signal
molecule
Signal
molecule
Helix in the
Membrane
Tyr
Tyrosines
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
CYTOPLASM
Tyr
Dimer
Figure 11.7
Activated
relay proteins
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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
Signal
molecule
(ligand)
Gate closed
Ligand-gated
ion channel receptor
Ions
Plasma
Membrane
Gate open
Cellular
response
Gate close
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Figure 11.7
*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?
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
mRNA
NUCLEUS
Figure 11.6
hormone testosterone
passes through the
plasma membrane.
2 Testosterone binds
to a receptor protein
in the cytoplasm,
activating it.
3 The hormone-
receptor complex
enters the nucleus
and binds to specific
genes.
DNA
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1 The steroid
CYTOPLASM
New protein
4
The bound protein
stimulates the
transcription of
the gene into mRNA.
5 The mRNA is
translated into a
specific protein.
Step Two - Transduction
 Signal initiated by conformational change
of receptor protein
 Signal is turned into a cellular response.
 Signaling cascades relay signals to target
 Multistep pathways can amplify a signal

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Second messengers involved
 A phosphorylation cascade
Signal molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
Active
protein
kinase
1
Inactive
protein kinase
2
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.
ATP
ADP
Pi
PP
3 Active protein kinase 2
then catalyzes the phosphorylation (and activation) of
protein kinase 3.
P
Active
protein
kinase
2
Inactive
ATP
protein kinase
ADP
Enzymes
called
protein
3
5
phosphatases (PP)
catalyze the removal of
PP
Pi
the phosphate groups
from the proteins,
making them inactive
Inactive
and available for reuse.
protein
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
Figure 11.8
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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
transcription
 Signaling pathways regulate a
variety of cellular activities
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Pathways can regulate genes by activating
transcription factors that turn genes on or
off
Growth factor
Receptor
Phosphorylation
cascade
Reception
Transduction
CYTOPLASM
Inactive
transcription Active
transcription
factor
factor
P
Response
Figure 11.14
DNA
Gene
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NUCLEUS
mRNA
Evolutionary Significance
 Unicellular and multicellular cell
communication have similarities
 Yeast cells signal for sexual
reproduction through signal
transduction process.
 Bacteria secrete molecules to sense
density of own population.

Quorum Sensing (survival purpose)
TEDED on Quorum Sensing
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