John Girard
Project Opening Doors
 Cells communicate by chemical
“messengers”
 Animal and plant cells have cell junctions
that directly connect the cytoplasm of
adjacent cells
 In local signaling, animal cells and
unicellular organisms may communicate by
direct contact, called cell-cell recognition
 Animal cells communicate using local
regulators, messenger molecules that
travel only short distances
 In long-distance signaling, plants and
animals use chemicals called hormones
Local and Long-Distance Cell Communication in Animals
Local and Long-Distance Cell Communication in Animals
Local and Long-Distance Cell Communication in Animals
Communication by Direct Contact between Cells
Communication by Direct Contact between Cells
Cell Communication
 A signal transduction pathway is a series of steps
by which a signal on a cell’s surface is
converted into a specific cellular
response
 Cells receiving signals go through
three processes:
 Reception
 Transduction
 Response
Overview of Cell Signaling
Overview of Cell Signaling
Overview of Cell Signaling
Receptors in the Plasma Membrane
 There are three main types of
membrane receptors:
 G protein-coupled receptors
 Tyrosine kinase receptors
 Ion channel receptor
The Structure of a G-Protein-coupled Receptor
The Functioning of a G-Protein-coupled Receptor
The Functioning of a G-Protein-coupled Receptor
The Functioning of a G-Protein-coupled Receptor
The Functioning of a G-Protein-coupled Receptor
Activity: Pathways with Friends
Instructions
1. Form groups of 6 people each
2. Create space for your group to interact without
bumping into each other
3. Rules:
 Each person in the group will get a card
 Do not let others in your group know what your
card says
 When prompted, follow the instructions on the
card
The Functioning of a G-Protein-coupled Receptor
Activity: Pathways with Friends
The Functioning of a G-Protein-coupled Receptor
Activity: Pathways with Friends
The Functioning of a G-Protein-Coupled Receptor
Activity:
The Functioning of a G-Protein-Coupled Receptor
Activity:
Receptors in the Plasma Membrane
 Tyrosine-kinase receptors are
membrane receptors that attach
phosphates to tyrosines
 A tyrosine-kinase receptor can trigger
multiple signal transduction pathways
at once
The Structure and Function of a Tyrosine-Kinase
Receptor
The Structure and Function of a Tyrosine-Kinase
Receptor
The Structure and Function of a Tyrosine-Kinase
Receptor
Activity:
The Structure and Function of a Tyrosine-Kinase
Receptor
Activity:
A Ligand-Gated Ion-Channel Receptor
A Ligand-Gated Ion-Channel Receptor
A Ligand-Gated Ion-Channel Receptor
Steroid Hormone Interacting
with an Intracellular Receptor
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
DNA
NUCLEUS
CYTOPLASM
Steroid Hormone Interacting
with an Intracellular Receptor
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
NUCLEUS
CYTOPLASM
Steroid Hormone Interacting
with an Intracellular Receptor
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
DNA
NUCLEUS
CYTOPLASM
Responses to Other Signals
Inner
chamber
–90 mV
+62 mV
Outer
chamber
140 mM
15 mM
NaCI
5 mM
KCI
KCI
150 mM
NaCI
Cl–
K+
Cl–
Potassium
channel
(a) Membrane selectively permeable to K+
Na+
Sodium
channel
(b) Membrane selectively permeable to Na+
Responses to Other Signals
1
Reception
2
Transduction
CYTOPLASM
Plasma
membrane
cGMP
Second messenger
produced
Phytochrome
activated
by light
Cell
wall
Light
Specific
protein
kinase 1
activated
NUCLEUS
Responses to Other Signals
1
Reception
2
Transduction
CYTOPLASM
Plasma
membrane
cGMP
Second messenger
produced
Specific
protein
kinase 1
activated
Phytochrome
activated
by light
Cell
wall
Specific
protein
kinase 2
activated
Light
Ca2+ channel
opened
Ca2+
NUCLEUS
Responses to Other Signals
1
Reception
2
Transduction
3
Response
Transcription
factor 1
CYTOPLASM
Plasma
membrane
cGMP
Second messenger
produced
Specific
protein
kinase 1
activated
NUCLEUS
P
Transcription
factor 2
Phytochrome
activated
by light
P
Cell
wall
Specific
protein
kinase 2
activated
Transcription
Light
Translation
Ca2+ channel
opened
Ca2+
De-etiolation
(greening)
response
proteins
Signal Transduction Pathways
 Protein kinases transfer phosphates from
ATP to protein, a process called
phosphorylation
Signal Transduction Pathways
 Protein phosphatases remove the
phosphates from proteins, a process
called dephosphorylation
 This phosphorylation and dephosphorylation system acts as a
molecular switch, turning activities on and off
A Phosphorylation Cascade
Signaling
molecule
Receptor
Activated relay
molecule
A Phosphorylation Cascade
Signaling
molecule
Receptor
Inactive
protein kinase
1
Activated relay
molecule
Active
protein
kinase
1
A Phosphorylation Cascade
Signaling
molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
Active
protein
kinase
1
Inactive
protein kinase
2
Pi
ATP
ADP
PP
Active
protein
kinase
2
P
A Phosphorylation Cascade
Signaling
molecule
Receptor
Activated relay
molecule
Inactive
protein kinase
1
Active
protein
kinase
1
Inactive
protein kinase
2
ATP
ADP
Pi
Active
protein
kinase
2
PP
Inactive
protein kinase
3
Pi
P
ATP
ADP
PP
Active
protein
kinase
3
P
A Phosphorylation Cascade
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
Pi
PP
Active
protein
Cellular
respons
e
Second Messengers
 The extracellular signal molecule that
binds to the receptor is a pathway’s
first messenger
 Second messengers are small,
nonprotein, water-soluble molecules or
ions that spread throughout a cell by
diffusion
Second Messengers
 Cyclic AMP (cAMP) is one of the most
widely used second messengers
 Adenylyl cyclase, an enzyme in the
plasma membrane, converts ATP to
cAMP in response to an extracellular
signal
cAMP as a Second Messenger
First messenger
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Second
messenger
Protein
kinase A
Cellular responses
Epinephrine Transduction Pathway
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Second
messenger
Epinephrine Transduction Pathway
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Inhibition of
glycogen synthesis
Promotion of
glycogen breakdown
Protein
kinase A
Second
messenger
cAMP as a Second Messenger
Activity:
cAMP as a Second Messenger
Activity:
Calcium Ions
 Calcium ions (Ca2+) act as a second
messenger in many pathways
 Calcium is an important second
messenger because cells can regulate
its concentration
The Maintenance of Calcium Ion Concentrations
in an Animal Cell
High Ca++
Low Ca++
Inositol Triphosphate
 Pathways leading to the release of
calcium involve inositol triphosphate
(IP3) and diacylglycerol (DAG) as
additional second messengers
Calcium and Inositol Triphosphate in Signaling
Pathways
EXTRACELLULAR
FLUID
Signaling molecule
(first messenger)
G protein
DAG
GTP
G protein-coupled
receptor
Phospholipase C
PIP2
IP3
(second messenger)
IP3-gated
calcium channel
Endoplasmic
reticulum (ER)
CYTOSOL
Ca2+
Calcium and Inositol Triphosphate in Signaling
Pathways
EXTRACELLULAR
FLUID
Signaling molecule
(first messenger)
G protein
DAG
GTP
G protein-coupled
receptor
Phospholipase C
PIP2
IP3
(second messenger)
IP3-gated
calcium channel
Endoplasmic
reticulum (ER)
CYTOSOL
Ca2+
Ca2+
(second
messenger)
Calcium and Inositol Triphosphate in Signaling
Pathways
EXTRACELLULAR
FLUID
Signaling molecule
(first messenger)
G protein
DAG
GTP
G protein-coupled
receptor
Phospholipase C
PIP2
IP3
(second messenger)
IP3-gated
calcium channel
Endoplasmic
reticulum (ER)
CYTOSOL
Various
proteins
activated
Ca2+
Ca2+
(second
messenger)
Cellular
responses
Growth factor
Reception
Receptor
Nuclear Response
to a Signal: The
Activation of a
Specific Gene by a
Growth Factor
Phosphorylatio
n
cascade
Transduction
CYTOPLASM
Inactive
transcription
factor
Active
transcription
factor
P
Response
DNA
Gene
NUCLEUS
mRNA
Signal Amplification: Stimulation of Glycogen Breakdown by
Epinephrine
Is Signal Transduction Important?
Androgen Insensitivity
Syndrome:
Genetic male (XY) without androgen receptors
The gene for the syndrome is on the X chromosome in band Xq11-q12.
The gene codes for the androgen receptor.
Result: No signal transduction!
Cell Communication Free-Response
Questions
1992
2. Biological recognition is important in many processes at the
molecular, cellular, tissue, and organismal levels. Select three of the
following, and for each of the three that you have chosen, explain
how the process of recognition occurs and give an example.
a) Organisms recognize others as members of their own
species.
b) Neurotransmitters are recognized in the synapse.
c) Antigens trigger antibody responses.
d) Nucleic acids are complementary.
e) Target cells respond to specific hormone
Cell Communication Free-Response
Questions
1999
2. Communication occurs among the cells in a multicellular
organism. Choose THREE of the following examples of cell-to-cell
communication, and for each example, describe the communication
that occurs and the types of responses that result from this
communication.
a) Communication between two plant cells
b) Communication between two immune-system cells
c) Communication either between a neuron and another
neuron, or between a neuron and a muscle cell
d) Communication between a specific endocrine-gland cell and
its target cell
Cell Communication Free-Response
Questions
2007
1. Membranes are essential components of all cells.
a) Identify THREE macromolecules that are components of the
plasma membrane in a eukaryotic cell and discuss the
structure and function of each.
b) Explain how membranes participate in THREE of the
following biological processes:
• Muscle contraction
• Fertilization of an egg
• Chemiosmotic production of ATP
• Intercellular signaling
Cell Communication Free-Response
Questions
2008
1. The physical structure of a protein often reflects and affects its
function.
a) Describe THREE types of chemical bonds/interactions found
in proteins. For each type, describe its role in determining
protein structure.
b) Discuss how the structure of a protein affects the function of
TWO of the following.
• Muscle contraction
• Regulation of enzyme activity
• Cell signaling
c) Abnormal hemoglobin is the identifying characteristic of
sickle cell anemia. Explain the genetic basis of the abnormal
hemoglobin. Explain why the sickle cell allele is selected for
in certain areas of the world.