Download Cell_Comm_Ch11_2015 - Kenston Local Schools

Cell Communication
 Cell-to-cell
communication is
important for multicellular
organisms
Exchange of
mating factors
a factor
Receptor
a
a
Yeast cell, a factor
mating type a
Yeast cell,
mating type a
Mating
a
a
New a/a cell
a/a



https://www.youtube.com/watch?v=TfpOKW
dOolM
(Start at 3:40 - ~ 6:00)
https://www.youtube.com/watch?v=DY3SQA
79ZVo (only 1 second)
 chemical
messengers
 cell junctions directly connect
adjacent cells
 In local signaling, animal cells
may communicate by direct
contact
Plasma membranes
Gap junctions
between animal cells
Cell junctions
Cell-cell recognition
Plasmodesmata
between plant cells
 Animals
use local regulators (for
short distance signals)
◦ EX: Humans: pass a note; text
message; Celly; email; Facebook
 Plants
and animals use chemicals
called hormones (for long distance)
Local signaling
Long-distance signaling
Target cell
Secreting
cell
Local regulator
diffuses through
extracellular fluid
Paracrine signaling
Electrical signal
along nerve cell
triggers release of
neurotransmitter
Endocrine cell
Neurotransmitter
diffuses across
synapse
Secretory
vesicle
Target cell
is stimulated
Blood
vessel
Hormone travels
in bloodstream
to target cells
Target
cell
Synaptic signaling
Hormonal signaling

http://www.bozemanscience.com/037-cellcommunication
 Earl
Sutherland discovered how
the hormone epinephrine acts
on cells

http://media.pearsoncmg.com/bc/bc_campbell_biology_7/mm2
/ch11/InstructorResources/medialib_tab_2/1.htm
◦Reception
◦Transduction
◦Response
◦ http://media.pearsoncmg.com/bc/bc_campbell_biology_7/
mm2/ch11/InstructorResources/medialib_tab_2/2.htm
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane
Reception
Receptor
Signal
molecule
Transduction
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane
Reception
Transduction
Receptor
Relay molecules in a signal transduction
pathway
Signal
molecule
EXTRACELLULAR
FLUID
CYTOPLASM
Plasma membrane
Reception
Transduction
Response
Receptor
Activation
of cellular
response
Relay molecules in a signal transduction
pathway
Signal
molecule
The binding between a signal molecule
(ligand) and receptor is specific
 A conformational (shape) change in a
receptor starts the process
 Most signal receptors are plasma
membrane proteins


Small or hydrophobic chemical messengers
can readily cross the membrane and activate
receptors
◦ Examples of hydrophobic messengers are the
steroid and thyroid hormones of animals

An activated hormone-receptor complex can
act as a transcription factor, turning on
specific genes
Hormone
(testosterone)
EXTRACELLULAR
FLUID
Plasma
membrane
Receptor
protein
Hormonereceptor
complex
The steroid
hormone testosterone
passes through the
plasma membrane.
Testosterone binds
to a receptor protein
in the cytoplasm,
activating it.
The hormonereceptor complex
enters the nucleus
and binds to specific
genes.
DNA
The bound protein
stimulates the
transcription of
the gene into mRNA.
mRNA
NUCLEUS
New protein
The mRNA is
translated into a
specific protein.
CYTOPLASM

https://www.youtube.com/watch?v=qOVkedx
DqQo (bozeman signal transduction)
Most water-soluble signal molecules
bind to specific sites on receptor
proteins in the plasma membrane
 There are three main types of
membrane receptors:

1. G-protein-linked receptors
2. Receptor tyrosine kinases
3. Ion channel receptors
A
G-protein-linked receptor is a
plasma membrane receptor that
works with the help of a G protein
 The
G-protein acts as an on/off
switch:
 If GDP is bound to the G protein, the G
protein is inactive
Signal-binding site
Segment that
interacts with
G proteins
G-protein-linked receptor
 Receptor
tyrosine kinases are
membrane receptors that attach
phosphates to tyrosines
 A receptor tyrosine kinase can
trigger multiple signal transduction
pathways at once
Signal
molecule
Signal-binding site
a Helix in the
membrane
Signal
molecule
Tyrosines
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
Receptor tyrosine
kinase proteins
(inactive monomers)
CYTOPLASM
Dimer
Activated relay
proteins
Tyr
Tyr
Tyr
Tyr
Tyr
Tyr
6
ATP
Activated tyrosinekinase regions
(unphosphorylated
dimer)
6 ADP
P Tyr
P Tyr
P Tyr
Tyr
P
P
Tyr P
Tyr
Fully activated receptor
tyrosine-kinase
(phosphorylated
dimer)
P Tyr
P Tyr
P Tyr
P
Tyr P
Tyr P
Tyr
Inactive
relay proteins
Cellular
response 1
Cellular
response 2
 An
ion channel receptor acts as a
gate when the receptor changes
shape
 When a signal molecule binds as a
ligand to the receptor, the gate
allows specific ions, such as Na+ or
Ca2+, through a channel in the
receptor
Signal
molecule
(ligand)
Gate
closed
Ligand-gated
ion channel receptor
Ions
Plasma
membrane
Gate open
Cellular
response
Gate closed

https://www.youtube.com/watch?v=_GraY9A
8N4Q
 Transduction
usually involves
multiple steps
 Multistep pathways can amplify
a signal: A few molecules can
produce a large cellular
response
The molecules that relay a signal from
receptor are mostly proteins
 Like falling dominoes, the receptor
activates another protein, which
activates another, and so on, until the
protein producing the response is
activated

 In
many pathways, the signal is
transmitted by a cascade of protein
phosphorylations
 Turning activities on and off
Signal 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 are small,
nonprotein, water-soluble molecules or
ions
◦ The extracellular signal molecule that binds to the
membrane is a pathway’s “first messenger”
◦ Second messengers can spread through cells by
diffusion
◦ Second messengers are important in G-protein-linked
receptors and tyrosine kinases
•
•
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
Phosphodiesterase
Adenylyl cyclase
Pyrophosphate
P
ATP
H2O
Pi
Cyclic AMP
AMP
 Many
signal molecules trigger
formation of cAMP
First messenger
(signal molecule
such as epinephrine)
Adenylyl
cyclase
G protein
G-protein-linked
receptor
GTP
ATP
cAMP
Second
messenger
Protein
kinase A
Cellular responses
 Calcium
ions (Ca2+) act as a second
messenger in many pathways
 Calcium is an important second
messenger because cells can
regulate its concentration
EXTRACELLULAR
FLUID
Plasma
membrane
Ca2+
pump
ATP
Mitochondrion
Nucleus
CYTOSOL
Ca2+
pump
Endoplasmic
reticulum (ER)
ATP
Key
Ca2+
pump
High [Ca2+]
Low [Ca2+]
EXTRACELLULAR Signal molecule
FLUID
(first messenger)
G protein
DAG
GTP
G-protein-linked
receptor
IP3-gated
calcium channel
Endoplasmic
Ca2+
reticulum (ER)
CYTOSOL
Phospholipase C
PIP2
IP3 (second
messenger)
EXTRACELLULAR Signal molecule
FLUID
(first messenger)
G protein
DAG
GTP
G-protein-linked
receptor
Phospholipase C
IP3 (second
messenger)
IP3-gated
calcium channel
Endoplasmic
Ca2+
reticulum (ER)
CYTOSOL
PIP2
Ca2+
(second
messenger)
EXTRACELLULAR Signal molecule
FLUID
(first messenger)
G protein
DAG
GTP
G-protein-linked
receptor
Phospholipase C
PIP2
IP3 (second
messenger)
IP3-gated
calcium channel
Endoplasmic
Ca2+
reticulum (ER)
CYTOSOL
Ca2+
(second
messenger)
Various
proteins
activated
Cellular
responses
Reception
Binding of epinephrine to G-protein-linked receptor (1 molecule)
Transduction
Inactive G protein
Active G protein (102 molecules)
Inactive adenylyl cyclase
Active adenylyl cyclase (102)
ATP
Cyclic AMP (104)
Inactive protein kinase A
Active protein kinase A (104)
Inactive phosphorylase kinase
Active phosphorylase kinase (105)
Inactive glycogen phosphorylase
Active glycogen phosphorylase (106)
Response
Glycogen
Glucose-1-phosphate
(108 molecules)
GENE REGULATION:


Many other signaling pathways regulate the
synthesis of enzymes or other proteins,
usually by turning genes on or off in the
nucleus
The final activated molecule may function as
a transcription factor
Growth factor
Reception
Receptor
Phosphorylation
cascade
Transduction
CYTOPLASM
Inactive
transcription Active
transcription
factor
factor
P
Response
DNA
Gene
NUCLEUS
mRNA
Signal
molecule
Receptor
Relay
molecules
Response 1
Cell A. Pathway leads
to a single response
Response 2
Response 3
Cell B. Pathway branches,
leading to two responses
Activation
or inhibition
Response 4
Cell C. Cross-talk occurs
between two pathways
Response 5
Cell D. Different receptor
leads to a different response
LE 11-16
Signal
molecule
Plasma
membrane
Receptor
Three
different
protein
kinases
Scaffolding
protein
LE 11-16
Signal
molecule
Plasma
membrane
Receptor
Three
different
protein
kinases
Scaffolding
protein
Inactivation mechanisms are an
essential aspect of cell signaling
 When signal molecules leave the
receptor, the receptor reverts to its
inactive state


https://www.youtube.com/watch?v=DusAds_-lU