ap biology cell communication. ap biology communication methods cell-to-cell contact local...
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AP Biology
Cell CommunicationCell Communication
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Communication Communication MethodsMethods Cell-to-cell contact Local signaling Long distance signaling
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Cell-to-Cell Cell-to-Cell CommunicationsCommunications Cell junctions directly connect the
cytoplasm of adjacent cells Ex: cardiac cells for rhythmicity
Surface receptors can give/send information Ex: specific immune response
Plasma membranes
Plasmodesmatabetween plant cells
Gap junctionsbetween animal cells
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Local SignalingLocal Signaling Adjacent cells are signaled.
Chemical messengers released Ex: Neurotransmitters via neurons
(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.
(b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.
Local regulator diffuses through extracellular fluid
Target cell
Secretoryvesicle
Electrical signalalong nerve celltriggers release ofneurotransmitter
Neurotransmitter diffuses across
synapse
Target cellis stimulated
Local signaling
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Long Distance SignalingLong Distance Signaling Use of hormones
Both plants and animals use hormones (e.g. Insulin)
Can affect many cells in Other parts of the body
Protein or Steroid types Hormone travelsin bloodstreamto target cells
(c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells.
Long-distance signaling
Bloodvessel
Targetcell
Endocrine cell
Figure 11.4 C
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How Do Cells How Do Cells Communicate?Communicate? Signal Transduction Signal Transduction
PathwaysPathways Convert signals on a cell’s surface
into cellular responses Are similar in microbes and
mammals, suggesting an early origin
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EXTRACELLULARFLUID
Receptor
Signal molecule
Relay molecules in a signal transduction pathway
Plasma membraneCYTOPLASM
Activationof cellularresponse
Figure 11.5
3 Phases of Signal Transduction3 Phases of Signal Transduction
Reception1 Transduction2 Response3
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Step One - ReceptionStep One - Reception Reception occurs when a signal molecule
(ligand) binds to a receptor protein.Receptor protein is on the cell surface Ligand and receptor have a unique bonding
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Step Two - TransductionStep 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
Second messengers involved
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Signal molecule
Activeproteinkinase
1
Activeproteinkinase
2
Activeproteinkinase
3
Inactiveprotein kinase
1
Inactiveprotein kinase
2
Inactiveprotein kinase
3
Inactiveprotein
Activeprotein
Cellularresponse
Receptor
P
P
P
ATPADP
ADP
ADP
ATP
ATP
PP
PP
PP
Activated relaymolecule
i
Phosphorylation cascade
P
P
i
i
P
A phosphorylation cascade
Figure 11.8
A relay moleculeactivates protein kinase 1.
1
2 Active protein kinase 1transfers a phosphate from ATPto an inactive molecule ofprotein kinase 2, thus activatingthis second kinase.
Active protein kinase 2then catalyzes the phos-phorylation (and activation) ofprotein kinase 3.
3
Finally, active proteinkinase 3 phosphorylates aprotein (pink) that brings about the cell’s response tothe signal.
4 Enzymes called proteinphosphatases (PP)catalyze the removal ofthe phosphate groupsfrom the proteins, making them inactiveand available for reuse.
5
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ATP
GTP
cAMP
Proteinkinase A
Cellular responses
G-protein-linkedreceptor
AdenylylcyclaseG protein
First messenger(signal moleculesuch as epinephrine)
Cyclic AMP example…
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321
IP3 quickly diffuses throughthe cytosol and binds to an IP3–gated calcium channel in the ERmembrane, causing it to open.
4 The calcium ionsactivate the nextprotein in one or moresignaling pathways.
6 Calcium ions flow out ofthe ER (down their con-centration gradient), raisingthe Ca2+ level in the cytosol.
5
DAG functions asa second messengerin other pathways.
Phospholipase C cleaves aplasma membrane phospholipidcalled PIP2 into DAG and IP3.
A signal molecule bindsto a receptor, leading toactivation of phospholipase C.
EXTRA-CELLULARFLUID
Signal molecule(first messenger)
G protein
G-protein-linkedreceptor
Variousproteinsactivated
Endoplasmicreticulum (ER)
Phospholipase C
PIP2
IP3
(second messenger)
DAG
Cellularresponse
GTP
Ca2+
(second messenger)
Ca2+
IP3-gatedcalcium channel
Ex: Inositol P3
and calcium
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Step Three - ResponseStep Three - Response Cell signaling leads to regulation of
cytoplasmic activities or transcription
Signaling pathways regulate a variety of cellular activities
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Pathways can also regulate genes by activating transcription factors that turn genes on or off
Reception
Transduction
Response
mRNANUCLEUS
Gene
P
Activetranscriptionfactor
Inactivetranscriptionfactor
DNA
Phosphorylationcascade
CYTOPLASM
Receptor
Growth factor
Figure 11.14
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There are three main types of plasma membrane receptors:G-protein-linkedTyrosine kinasesIon channel
Types of ReceptorsTypes of Receptors
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G-protein-linked receptorsG-protein-linked receptors Very common, diverse functions Only results in single pathway
response
G-protein-linkedReceptor
Plasma Membrane
EnzymeG-protein(inactive)CYTOPLASM
Cellular response
Activatedenzyme
ActivatedReceptor
Signal molecule Inactivateenzyme
GDP
GDP
GTP
GTP
P i
GDP
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Receptor tyrosine kinasesReceptor tyrosine kinases Multiple pathway response Regulates/coordinates many cell
functionsSignalmolecule
Signal-binding site
CYTOPLASM
Tyrosines
Signal moleculeHelix in the
Membrane
TyrTyrTyr
TyrTyr
Tyr TyrTyrTyr
TyrTyr
Tyr
TyrTyrTyr
TyrTyr
Tyr TyrTyrTyr
TyrTyr
Tyr
TyrTyrTyr
TyrTyr
Tyr
DimerReceptor tyrosinekinase proteins(inactive monomers)
PPP
PP
P TyrTyrTyr
TyrTyr
TyrPPP
PP
PCellularresponse 1
Inactiverelay proteins
Activatedrelay proteins
Cellularresponse 2
Activated tyrosine-kinase regions(unphosphorylateddimer)
Fully activated receptortyrosine-kinase(phosphorylateddimer)
6 ATP 6 ADP
Figure 11.7
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Ion channel receptorsIon channel receptors
Cellularresponse
Gate open
Gate close
Ligand-gatedion channel receptor
Plasma Membrane
Signalmolecule(ligand)
Figure 11.7
Gate closed Ions
When ligand binds, channel can open or close.
Ex: neurotransmitters bind as ligands for ion channels
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Hormone(testosterone)
EXTRACELLULARFLUID
Receptorprotein
DNA
mRNA
NUCLEUS
CYTOPLASM
Plasmamembrane
Hormone-receptorcomplex
New protein
Figure 11.6
*Intracellular Receptors*Intracellular Receptors Target protein is INSIDE the cell Must be hydrophobic molecule
1 The steroid hormone testosterone passes through the plasma membrane.
The bound proteinstimulates thetranscription ofthe gene into mRNA.
4
The mRNA istranslated into aspecific protein.
5
Testosterone bindsto a receptor proteinin the cytoplasm,activating it.
2
The hormone-receptor complexenters the nucleusand binds to specific genes.
3
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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)
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Yeast Sexual ReproductionYeast Sexual Reproduction
factorReceptor
Exchange of mating factors. Each cell type secretes a mating factor that binds to receptors on the other cell type.
1
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.
2
3
factorYeast cell,mating type a
Yeast cell,mating type
a/
a
a
Yeast cells identify their mates by cell
signaling.
Suggests early evidence of cell
signaling.