Transcript Cell signaling PPT – Examples from all chapters

Cell Signaling
Specific Examples from Animal and
Plant Biology
Regulation by chemical messengers
• Neurotransmitters released by neurons
• Hormones release by endocrine glands
endocrine gland
neurotransmitter
axon
hormone carried
by blood
receptor proteins
receptor proteins
target cell
Lock & Key
system
Action of lipid (steroid) hormones
steroid hormone
target cell
S
S
cytoplasm
blood
1
S
protein
carrier
cross cell membrane
2
binds to receptor protein
becomes
transcription factor
5
S
3
mRNA read by ribosome
plasma membrane
DNA
nucleus
4
mRNA
6
protein
7
protein secreted
ex: secreted protein = growth factor (hair, bone, muscle, gametes)
signal-transduction pathway
Action of protein hormones
1
protein
hormone
P
signal
plasma membrane
activates
G-protein
binds to receptor protein
activates enzyme
cAMP
receptor
protein
activates
cytoplasmic
signal
cytoplasm
target cell
GTP
acts as 2° messenger
transduction
ATP
ATP
activates
enzyme
2
secondary
messenger
system
activates
enzyme
produces an action
3
response
Ex: Action of epinephrine (adrenaline)
adrenal gland
signal
1
epinephrine
activates
G protein
receptor
protein
in cell
membrane
activates GTP
3
activates
adenylyl cyclase
cAMP
GDP
transduction
4
GTP
2
ATP
activates
protein kinase-A
5
activates
phosphorylase kinase
cytoplasm
liver cell
released
to blood
activates
glycogen phosphorylase
glycogen
6
glucose
7
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!
FAST response!
7
amplification
product
Transmission of a signal
• Think dominoes!
– start the signal
• knock down line of dominoes by tipping 1st one
 trigger the signal
– propagate the signal
• do dominoes move down the line?
 no, just a wave through them!
– re-set the system
• before you can do it again,
have to set up dominoes again
 reset the axon
Transmission of a nerve signal
• Neuron has similar system
– protein channels are set up
– once first one is opened, the rest open in
succession
• all or nothing response
– a “wave” action travels along neuron
– have to re-set channels so neuron can react
again
Cells: surrounded by charged ions
• Cells live in a sea of charged ions
– anions (negative)
• more concentrated within the cell
• Cl-, charged amino acids (aa-)
– cations (positive)
• more concentrated in the extracellular fluid
• Na+
K+
aa-
K+
aaCl-
Na+
ClK+
Na+
aa-
Na+
K+
aa-
K+
Na+
ClCl-
Na+
aa-
Na+
Na+
Cl-
aa- Cl-
Na+
–
Na+
Na+
Na+
+
K+
channel
leaks K+
Cells have voltage!
• Opposite charges on opposite sides of cell
membrane
– membrane is polarized
• negative inside; positive outside
• charge gradient
• stored energy (like a battery)
+ + + + + + + + + + + + + + +
– – – – – – – – – – – – – –
– – – – – – – – – – – – – –
+ + + + + + + + + + + + + + +
Measuring cell voltage
unstimulated neuron = resting potential of -70mV
How does a nerve impulse travel?
• Stimulus: nerve is stimulated
– reaches threshold potential
• open Na+ channels in cell membrane
• Na+ ions diffuse into cell
– charges reverse at that point on neuron
The 1st
domino
goes
down!
• positive inside; negative outside
• cell becomes depolarized
– + + + + + + + + + + + + + +
+ – – – – – – – – – – – – – –
Na+
+ – – – – – – – – – – – – – –
– + + + + + + + + + + + + + +
How does a nerve impulse travel?
• Wave: nerve impulse travels down neuron
– change in charge opens
+ –
+
next Na gates down the line
• “voltage-gated” channels
channel
– Na+ ions continue to diffuse into cell
closed
– “wave” moves down neuron = action potential
Gate
The rest
of the
dominoes
fall!
+
+
channel
open
– – – + + + + + + + + + + + +
+ + + – – – – – – – – – – – –
Na+
+ + + – – – – – – – – – – – –
– – – + + + + + + + + + + + +
wave

How does a nerve impulse travel?
• Re-set: 2nd wave travels down neuron
– K+ channels open
• K+ channels open up more slowly than Na+ channels
– K+ ions diffuse out of cell
– charges reverse back at that point
• negative inside; positive outside
Set
dominoes
back up
quickly!
K+
+ – – – – + + + + + + + + + +
– + + + + – – – – – – – – – –
Na+
– + + + + – – – – – – – – – –
+ – – – – + + + + + + + + + +
wave

How does a nerve impulse travel?
• Combined waves travel down neuron
– wave of opening ion channels moves down neuron
– signal moves in one direction     
• flow of K+ out of cell stops activation of Na+ channels in
wrong direction
Ready
for
next time!
K+
+ + + – – – – + + + + + + + +
– – – + + + + – – – – – – – –
Na+
– – – + + + + – – – – – – – –
+ + + – – – – + + + + + + + +
wave

How does a nerve impulse travel?
• Action potential propagates
– wave = nerve impulse, or action potential
– brain  finger tips in milliseconds!
In the
blink of
an eye!
K+
+ + + + + + + – – – – + + + +
– – – – – – – + + + + – – – –
Na+
– – – – – – – + + + + – – – –
+ + + + + + + – – – – + + + +
wave

Voltage-gated channels
• Ion channels open & close in response to changes in
charge across membrane
– Na+ channels open quickly in response to depolarization &
close slowly
– K+ channels open slowly in response to depolarization &
close slowly
Structure
& function!
K+
+ + + + + + + + + – – – + + +
– – – – – – – – – + + + – – –
Na+
– – – – – – – – – + + + – – –
+ + + + + + + + + – – – + + +
wave

How does the nerve re-set itself?
• After firing a neuron has to re-set itself
– Na+ needs to move back out
– K+ needs to move back in
– both are moving against concentration gradients
• need a pump!!
A lot of
work to
do here!
K+
+
Na
Na+
K+
Na+
K+
+
K
Na+
Na+
Na+
K+
Na+
+
Na
+
Na+ Na
+ + + + + + + + + + – – – – +
– – +– – – – – – – – + + + + –
Na+
Na
K+
K+
K++
Na
+
Na+
K
+
Na+
K+ K
K+
Na+
Na+
K+
– – – – – – – – – – + + + + –
+ + + + + + + + + + – – – – +
wave

Na+
How does the nerve re-set itself?
• Sodium-Potassium pump
– active transport protein in membrane
• requires ATP
– 3 Na+ pumped out
– 2 K+ pumped in
– re-sets charge
across
membrane
That’s a lot
of ATP !
Feed me some
sugar quick!
ATP
Neuron is ready to fire again
Na+
Na+
Na+
K+
aa-
aaNa+
Na+
Na+
K+
Na+
Na+
K+
Na+
aa-
K+
Na+
Na+
Na+
Na+
K+
aaNa+
Na+
Na+
K+
Na+
Na+
Na+
K+
aa-
aa- K+
K+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
resting potential
+ + + + + + + + + + + + + + +
– – – – – – – – – – – – – – –
– – – – – – – – – – – – – – –
+ + + + + + + + + + + + + + +
Action potential graph
40 mV
4
30 mV
20 mV
Membrane potential
1. Resting potential
2. Stimulus reaches threshold
potential
3. Depolarization
Na+ channels open;
K+ channels closed
4. Na+ channels close;
K+ channels open
5. Repolarization
reset charge gradient
6. Undershoot
K+ channels close slowly
10 mV
0 mV
Depolarization
Na+ flows in
–10 mV
3
Repolarization
K+ flows out
5
–20 mV
–30 mV
–40 mV
–50 mV
–60 mV
–70 mV
–80 mV
Hyperpolarization
(undershoot)
Threshold
2
1
Resting potential
6 Resting
What happens at the end of the axon?
Impulse has to jump the synapse!
– junction between neurons
– has to jump quickly from one cell to next
How does
the wave
jump the gap?
Synapse
Chemical synapse
axon terminal
 Events at synapse
action potential


synaptic vesicles

synapse


Ca++
receptor protein
neurotransmitter
acetylcholine (ACh)
muscle cell (fiber)
We switched…
from an electrical signal
to a chemical signal
action potential depolarizes membrane
opens Ca++ channels
neurotransmitter vesicles fuse with
membrane
release neurotransmitter to synapse 
diffusion
neurotransmitter binds with protein
receptor
 ion-gated channels open

neurotransmitter degraded or
reabsorbed
Nerve impulse in next neuron
K+
• Post-synaptic neuron
– triggers nerve impulse in next nerve cell
• chemical signal opens ion-gated channels
Na+
binding site
• Na+ diffuses into cell
• K+ diffuses out of cell
Here we
go again!
– switch back to
voltage-gated channel
ion channel
K+
ACh
K+
– + + + + + + + + + + + + + +
+ – – – – – – – – – – – – – –
Na+
+ – – – – – – – – – – – – – –
– + + + + + + + + + + + + + +
Na+
Na+
Neurotransmitters
• Acetylcholine
– transmit signal to skeletal muscle
• Epinephrine (adrenaline) & norepinephrine
– fight-or-flight response
• Dopamine
– widespread in brain
– affects sleep, mood, attention & learning
– lack of dopamine in brain associated with Parkinson’s
disease
– excessive dopamine linked to schizophrenia
• Serotonin
– widespread in brain
– affects sleep, mood, attention & learning
Neurotransmitters
• Weak point of nervous system
– any substance that affects neurotransmitters or
mimics them affects nerve function
• gases: nitrous oxide, carbon monoxide
• mood altering drugs:
– stimulants
» amphetamines, caffeine, nicotine
– depressants
» quaaludes, barbiturates
• hallucinogenic drugs: LSD, peyote
• SSRIs: Prozac, Zoloft, Paxil
• poisons
Chapter 39 Plant Responses
• A potato left growing in darkness produces
shoots that look unhealthy, and it lacks
elongated roots
• These are morphological adaptations for
growing in darkness, collectively called
etiolation
• After exposure to light, a potato undergoes
changes called de-etiolation, in which shoots
and roots grow normally
© 2011 Pearson Education, Inc.
Figure 39.4-3
2 Transduction
1 Reception
3 Response
Transcription
factor 1 NUCLEUS
CYTOPLASM
Plasma
membrane
cGMP
Second
messenger
Phytochrome
P
Protein
kinase 1
Transcription
factor 2
P
Cell
wall
Protein
kinase 2
Transcription
Light
Translation
Ca2 channel
Ca2
De-etiolation
(greening)
response proteins
Figure 39.UN03
Auxin (IAA)
• Effects
– controls cell division
& differentiation
– ___creates tropisms!__
• growth towards light
• asymmetrical distribution of auxin
• cells on darker side elongate faster
than cells on brighter side
– __Phototropism_______
The Role of Auxin in Cell Elongation
• According to the acid growth hypothesis, auxin
stimulates proton pumps in the plasma membrane
• The proton pumps lower the pH in the cell wall,
activating expansins, enzymes that loosen the wall’s
fabric
• With the cellulose loosened, the cell can elongate
© 2011 Pearson Education, Inc.
Figure 39.5
RESULTS
Shaded
side
Control
Light
Illuminated
side
Boysen-Jensen
Light
Darwin and Darwin
Light
Gelatin
(permeable)
Tip
removed
Opaque
cap
Transparent
cap
Opaque
shield over
curvature
Mica
(impermeable)
Ethylene
• Hormone gas released by plant cells
• Effects
–
–
–
–
response to mechanical stress
leaf abscission
fruit ripening
Apotosis - Senescence is the programmed death of
cells or organs
One bad apple
spoils the
whole bunch…
The Triple Response to Mechanical Stress
• Ethylene induces the triple response, which allows a
growing shoot to avoid obstacles
• The triple response consists of a slowing of stem
elongation, a thickening of the stem, and horizontal
growth
© 2011 Pearson Education, Inc.
Fruit ripening
• Adaptation
– hard, tart fruit protects
developing seed from herbivores
– ripe, sweet, soft fruit attracts
animals to disperse seed
• Mechanism
– triggers ripening process
• breakdown of cell wall
– softening
• conversion of starch to sugar
– sweetening
– positive feedback system
• ethylene triggers ripening
• ripening stimulates more ethylene production
– clusters of fruit ripen together
Phytochromes as Photoreceptors
• Phytochromes are pigments that regulate many of a
plant’s responses to light throughout its life
• These responses include seed germination and shade
avoidance
© 2011 Pearson Education, Inc.
Phytochromes and Seed Germination
• Many seeds remain dormant until light conditions
change
• In the 1930s, scientists at the U.S. Department of
Agriculture determined the action spectrum for lightinduced germination of lettuce seeds
© 2011 Pearson Education, Inc.
• Phytochromes exist in two photoreversible states,
with conversion of Pr to Pfr triggering many
developmental responses
• Red light triggers the conversion of Pr to Pfr
• Far-red light triggers the conversion of Pfr to Pr
• The conversion to Pfr is faster than the conversion to
Pr
• Sunlight increases the ratio of Pfr to Pr, and triggers
germination
© 2011 Pearson Education, Inc.
Photoperiodism and Responses to
Seasons
• Photoperiod, the relative lengths of night and day, is the
environmental stimulus plants use most often to detect
the time of year
• Critical Night Length - In the 1940s, researchers
discovered that flowering and other responses to
photoperiod are actually controlled by night length, not
day length
© 2011 Pearson Education, Inc.
Figure 39.22
24 hours
R
R FR
R FR R
R FR R FR
Critical dark period
Long-day
Short-day
(long-night) (short-night)
plant
plant
• Thigmotropism is growth in response to touch
• It occurs in vines and other climbing plants
• Another example of a touch specialist is the
sensitive plant Mimosa pudica, which folds its
leaflets and collapses in response to touch
• Rapid leaf movements in response to mechanical
stimulation are examples of transmission of
electrical impulses called action potentials
© 2011 Pearson Education, Inc.
Figure 39.26
(a) Unstimulated state
(b) Stimulated state
Side of pulvinus
with flaccid cells
Pulvinus
(motor
organ)
Side of pulvinus
with turgid cells
Vein
0.5 m
Leaflets
after
stimulation
(c) Cross section of a leaflet pair in the stimulated state (LM)
Figure 39.28
4 Recruitment of
parasitoid wasps
that lay their eggs
within caterpillars
1 Wounding
1 Chemical
in saliva
2 Signal transduction
pathway
3 Synthesis
and release
of volatile
attractants
Defenses Against Pathogens
• A plant’s first line of defense against infection is the
barrier presented by the epidermis and periderm
• If a pathogen penetrates the dermal tissue, the
second line of defense is a chemical attack that kills
the pathogen and prevents its spread
• This second defense system is enhanced by the
plant’s ability to recognize certain pathogens
© 2011 Pearson Education, Inc.
Figure 39.29
Infected tobacco leaf with lesions
4
3
Signal
5
Hypersensitive
response
Signal
transduction
pathway
6
2 Signal transduction pathway
7
Acquired
resistance
1
R protein
Avirulent
pathogen
Avr effector protein
R-Avr recognition and
hypersensitive response
Systemic acquired
resistance