Cell Communication
Big Idea 3: Living systems store, retrieve, transmit,
and respond to info essential to life processes.
Essential Knowledge
• 3D1: Cell communication processes share
common features that reflect evolutionary
history.
• 3D2: Cells communicate with each other through
direct contact with other cells or from a distance
via chemical signaling.
• 3D3: Signal transduction pathways link signal
reception with cellular response.
• 3D4: Changes in signal transduction pathways
can alter cellular responses.
Simple Communication
Stimulatory
•Activate some sort of
behavior, activity, gene
expression etc.
Inhibitory
•Shut off behavior,
activity, gene
expression etc.
Origin of Cell Signaling
•Began as way for single celled orgs to
“communicate” w/ each other
•Ex: when it gets crowded bacteria can send signals
to shut off reproduction (quorum sensing)
•Has been conserved throughout evolution
Purpose of Signaling in Multi-Cellular
Organisms
•Coordinate cellular
actions
•Ex: when frightened
you release
epinephrine, which
triggers mobilization
of glucose and other
energy resources
•Fight or flight
Distance of Communication
1) Direct contact
2) Local communication
3) Long distance
Example of Direct Contact
• Plant cells walls have plasmodesmata which
allow material to be transported b/t cells.
Example of Direct Contact
•Antigenpresenting White
blood cell directly
contacts helper T
cells
•Activates immune
responses
Example of Local Regulation
•Neurotransmitters
(chem messengeres
in b/t neurons)
•Serotonin, dopamine
etc. carry signals from
one part of brain to
others
•Only affects cells in
local area
Example of Long Distance Signaling
• Hormones
• Released from
endocrine glands
and travel
through blood
• Affect many
target cells
throughout the
body
Step 1: Reception
• Signal molecule (aka ligand) binds to a
receptor protein  change shape
• Highly specific
• Most signal receptors are proteins
Types of Receptors on Plasma Membrane
• Type 1: G protein-coupled receptor: membrane
receptor that works w/ help of a G
protein…(how gangsta!)
• G protein acts as an on/off switch: If GDP is
bound to G protein  G protein is inactive
• http://highered.mcgrawhill.com/sites/0072507470/student_view0/chap
ter17/animation__membranebound_receptors_that_activate_g_proteins.html
G Proteins and Medicine

Diabetes, blindness, allergies, depression and
some cancers are believed to come from
dysfunctional G proteins
 Up to 60% of medicines used influence GProtein Pathways
Types of Receptors on Plasma Membrane
• Type 2: Receptor tyrosine kinases: membrane
receptors that attach phosphates to tyrosines
(a.acids)
• Can trigger multiple signal pathways at once
Types of Receptors on Plasma Membrane
• Type 3: Ligandgated ion
channel
receptor acts as
a gate when
receptor
changes shape
Intracellular Receptors
• Some receptor proteins are found in
cytosol/nucleus of target cells
• Small/hydrophobic chemical messengers
can readily cross membrane and activate
receptors Ex: hormones!
http://highered.mcgrawhill.com/sites/0072507470/student_view0/chapter17/animation__intracellular_receptor_m
odel.html
Fig. 11-8-1
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
DNA
NUCLEUS
CYTOPLASM
Fig. 11-8-2
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
NUCLEUS
CYTOPLASM
Fig. 11-8-3
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
NUCLEUS
CYTOPLASM
Fig. 11-8-4
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
mRNA
NUCLEUS
CYTOPLASM
Fig. 11-8-5
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
mRNA
NUCLEUS
CYTOPLASM
New protein
Step 2: Transduction
• Multiple steps
• Can amplify a signal!
• Relayers are mainly proteins
• Domino effect!
Protein Phosphorylation and
Dephosphorylation
• Signal passed by a
cascade of protein
phosphorylations
• Protein kinases transfer
PO4’s from ATP to
protein
(phosphorylation)
• Protein phosphatases
remove PO4’s from
proteins
(dephosphorylation)
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
ATP
ADP
Pi
Active
protein
kinase
3
PP
Inactive
protein
P
ATP
P
ADP
Pi
PP
Active
protein
Cellular
response
Second Messengers
• 1st messenger:
bound onto cell
membrane
• 2nd messengers:
small, nonprotein,
water-soluble
molecules that
spread t/out a cell by
diffusion
• Exs: Cyclic AMP and
Ca+2 ions
Cyclic AMP
• Cyclic AMP (cAMP): most widely used 2nd
messenger
• Adenylyl cyclase: enzyme in plasma
membrane, converts ATP to cAMP in
response to an extracellular signal
• http://highered.mcgrawhill.com/sites/0072507470/student_view0/chap
ter17/animation__second_messenger__camp.ht
ml
Fig. 11-10
Adenylyl cyclase
Phosphodiesterase
Pyrophosphate
P
ATP
Pi
cAMP
AMP
Fig. 11-11
First messenger
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Second
messenger
Protein
kinase A
Cellular
responses
Step 3: Response
• AKA: “output
response”
• Usually
activates
transcription to
make a protein
or to regulate
enzyme activity.
Importance of Cell Signaling
• Diseases result from incorrect signaling
• Drugs often target signaling mechanisms
• Poisons and pesticides often target
signaling pathways
Mr. Anderson Cell Signaling