Cell Communication. Cell-to-cell communication is important for multicellular organisms.
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Transcript of Cell Communication. Cell-to-cell communication is important for multicellular organisms.
Cell Communication
Cell-to-cell communication is important for multicellular organisms
Exchange ofmating factors
Mating
Receptor
a
factor
a
a factorYeast cell,mating type a
Yeast cell,mating type
a/
New a/ cell
https://www.youtube.com/watch?v=TfpOKWdOolM
(Start at 3:40 - ~ 6:00) https://www.youtube.com/watch?
v=DY3SQA79ZVo (only 1 second)
chemical messengerscell junctions directly connect adjacent cells
In local signaling, animal cells may communicate by direct contact
Plasma membranes
Gap junctionsbetween animal cells
Cell junctions
Cell-cell recognition
Plasmodesmatabetween 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)
Paracrine signaling
Local regulatordiffuses throughextracellular fluid
Secretoryvesicle
Secretingcell
Target cell
Local signaling
Electrical signalalong nerve celltriggers release ofneurotransmitter
Neurotransmitter diffuses across synapse
Endocrine cell Bloodvessel
Long-distance signaling
Hormone travelsin bloodstreamto target cells
Synaptic signaling
Target cellis stimulated
Hormonal signaling
Target cell
http://www.bozemanscience.com/037-cell-communication
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
EXTRACELLULARFLUID
Reception
Plasma membrane
Transduction
CYTOPLASM
Receptor
Signalmolecule
EXTRACELLULARFLUID
Reception
Plasma membrane
Transduction
CYTOPLASM
Receptor
Signalmolecule
Relay molecules in a signal transductionpathway
EXTRACELLULARFLUID
Reception
Plasma membrane
Transduction
CYTOPLASM
Receptor
Signalmolecule
Relay molecules in a signal transductionpathway
Response
Activationof cellularresponse
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
EXTRACELLULARFLUID
Plasmamembrane
The steroidhormone testosteronepasses through theplasma membrane.
Testosterone bindsto a receptor proteinin the cytoplasm,activating it.
The hormone-receptor complexenters the nucleusand binds to specificgenes.
The bound proteinstimulates thetranscription ofthe gene into mRNA.
The mRNA istranslated into aspecific protein.
CYTOPLASM
NUCLEUS
DNA
Hormone(testosterone)
Receptorprotein
Hormone-receptorcomplex
mRNA
New protein
https://www.youtube.com/watch?v=qOVkedxDqQo (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 receptors2. Receptor tyrosine kinases3. 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
Segment thatinteracts withG proteins
Signal-binding site
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
Signalmolecule
Helix in themembrane
Signal-binding site
Tyr
Tyr
Tyr Tyr
Tyr
TyrTyrosines
Receptor tyrosinekinase proteins(inactive monomers)CYTOPLASM
Tyr
Tyr
Tyr Tyr
Tyr
Tyr Tyr
Tyr
Tyr Tyr
Tyr
Tyr
Tyr
Tyr
Tyr Tyr
Tyr
Tyr
Activated tyrosine-kinase regions(unphosphorylateddimer)
Signalmolecule
Dimer
Fully activated receptor tyrosine-kinase(phosphorylateddimer)
Tyr
Tyr
Tyr Tyr
Tyr
TyrPPP
PPPATP 6 ADP
Tyr
Tyr
Tyr Tyr
Tyr
TyrP
PP
PPP
Inactiverelay proteins
Cellularresponse 2
Cellularresponse 1
Activated relay proteins
6
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
Signalmolecule(ligand)
Gateclosed Ions
Ligand-gatedion channel receptor
Plasmamembrane
Gate closed
Gate open
Cellularresponse
https://www.youtube.com/watch?v=_GraY9A8N4Q
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
Activated relaymolecule
Receptor
Inactiveprotein kinase
1 Activeprotein kinase
1
Inactiveprotein kinase
2 Activeprotein kinase
2
Inactiveprotein kinase
3 Activeprotein kinase
3
ADP
Inactiveprotein
Activeprotein
Cellularresponse
Phosphorylation cascade
ATP
PPP i
ADPATP
PPP i
ADPATP
PPP i
P
P
P
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
ATP Cyclic AMP AMP
Adenylyl cyclase
PyrophosphateP P i
Phosphodiesterase
H2O
Many signal molecules trigger formation of cAMP
cAMP
ATPSecondmessenger
First messenger(signal moleculesuch as epinephrine)
G-protein-linkedreceptor
G protein
Adenylylcyclase
Proteinkinase A
Cellular responses
GTP
Calcium ions (Ca2+) act as a second messenger in many pathways
Calcium is an important second messenger because cells can regulate its concentration
ATP
EXTRACELLULARFLUID
ATP
Mitochondrion
Ca2+
pump
Plasmamembrane
CYTOSOL
Endoplasmicreticulum (ER)
Ca2+
pump
Ca2+
pump
High [Ca2+]Key
Nucleus
Low [Ca2+]
CYTOSOL
Ca2+Endoplasmicreticulum (ER)
IP3-gatedcalcium channel
IP3 (secondmessenger)
DAG
PIP2G-protein-linkedreceptor Phospholipase C
G protein
Signal molecule(first messenger)
EXTRACELLULARFLUID
GTP
CYTOSOL
Ca2+Endoplasmicreticulum (ER)
IP3-gatedcalcium channel
IP3 (secondmessenger)
DAG
PIP2G-protein-linkedreceptor Phospholipase C
G protein
Signal molecule(first messenger)
EXTRACELLULARFLUID
GTP
Ca2+ (secondmessenger)
CYTOSOL
Ca2+Endoplasmicreticulum (ER)
IP3-gatedcalcium channel
IP3 (secondmessenger)
DAG
PIP2G-protein-linkedreceptor Phospholipase C
G protein
Signal molecule(first messenger)
EXTRACELLULARFLUID
GTP
Ca2+ (secondmessenger)
Variousproteinsactivated
Cellularre-sponses
Binding of epinephrine to G-protein-linked receptor (1 molecule)
Reception
Transduction
Inactive G protein
Active G protein (102 molecules)
Inactive adenylyl cyclase
Active adenylyl cyclase (102)
ATP
Cyclic AMP (104)
Inactive protein kinase A
Inactive phosphorylase kinase
Active protein kinase A (104)
Active phosphorylase kinase (105)
Active glycogen phosphorylase (106)
Inactive glycogen phosphorylase
Glycogen
Response
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
ReceptionGrowth factor
Receptor
Phosphorylationcascade
Transduction
CYTOPLASM
Inactivetranscriptionfactor
Activetranscriptionfactor
PResponse
Gene
mRNA
DNA
NUCLEUS
Signalmolecule
Receptor
Relaymolecules
Response 1 Response 2 Response 3
Cell B. Pathway branches,leading to two responses
Cell A. Pathway leads to a single response
Cell C. Cross-talk occursbetween two pathways
Response 4 Response 5
Activationor inhibition
Cell D. Different receptorleads to a different response
LE 11-16
Signalmolecule
Plasmamembrane
Receptor
Scaffoldingprotein
Threedifferentproteinkinases
LE 11-16
Signalmolecule
Plasmamembrane
Receptor
Scaffoldingprotein
Threedifferentproteinkinases
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=D-usAds_-lU