Download AP Biology

Cell Communication
AP Biology
Communication Methods
 Cell-to-cell contact
 Local signaling
 Long distance signaling
AP Biology
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
AP Biology
Plasmodesmata
between plant cells
VIDEO
Local Signaling

VIDEO
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.
AP Biology
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
AP Biology
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
Both plants and animals
use hormones (e.g. Insulin)
Can affect many cells in
Other parts of the body


Long-distance signaling
Endocrine cell
 Protein or Steroid types
Blood
vessel
Hormone travels
in bloodstream
to target cells
Target
cell
AP Biology
Figure 11.4
(c) Hormonal signaling. Specialized
endocrine cells secrete hormones
into body fluids, often the blood.
Hormones may reach virtually all
C 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
AP Biology
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
AP Biology
Step One - Reception
 Reception occurs when a signal molecule
(ligand) binds to a receptor protein.
 Ligand and receptor have a unique bonding
AP Biology
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

AP Biology
Second messengers involved
Step Three - Response
 Cell signaling leads to regulation of
cytoplasmic activities or
transcription
 Signaling pathways regulate a
variety of cellular activities
AP Biology
 A phosphorylation cascade
Signal molecule
Receptor
Activated relay
molecule
Inactive
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
PP
Inactive
protein kinase
3
5 Enzymes called protein
phosphatases (PP)
catalyze the removal of
the phosphate groups
from the proteins,
making them inactive
and available for reuse.
Figure 11.8
P
Active
protein
kinase
2
ADP
Pi
AP Biology
1 A relay molecule
activates protein kinase 1.
3 Active protein kinase 2
then catalyzes the phosphorylation (and activation) of
protein kinase 3.
ATP
ADP
Pi
Active
protein
kinase
3
PP
Inactive
protein
P
4 Finally, active protein
kinase 3 phosphorylates a
protein (pink) that brings
about the cell’s response to
the signal.
ATP
ADP
Pi
PP
P
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!
AP Biologyresponse!
FAST
7
amplification
VIDEO
product
Pathways can also 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
AP Biology
NUCLEUS
mRNA
Types of Receptors
 There are three main types of
plasma membrane receptors:
 G-protein-linked
 Tyrosine kinases
 Ion channel
AP Biology
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
Signal molecule
GTP
Activated
enzyme
GTP
GDP
Pi
Cellular response
AP Biology
Inactivate
enzyme
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)
AP Biology
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
AP Biology
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?
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
AP Biology
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
 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
AP Biology