Cel Communication
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Transcript of Cel Communication
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Cell Communication
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Cell Communication
Communication between cells requires:
ligand: the signaling molecule
receptor protein: the molecule to which the
receptor binds-may be on the plasma membrane orwithin the cell
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Figure 15-1 Molecular Biology of the Cell( Garland Science 2008)
Intracellular signaling pathway activated byan extracellular signal molucule
The signal moleculebinds to receptor proteinon target cell.
One or more intracellularsignaling pathway isactivated by signalproteins.
Signaling proteins
activates effector proteinsdictating cell behaviour.
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Figure 15-2 Molecular Biology of the Cell( Garland Science 2008)
Budding yeast cells
responding to a mating factor Normal haploid cells
are spherical.
When ready to matemating factors aresecreted.
In response tomating factors
neighboring cells putout a protrusiontowards source offactor.
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Figure 15-3a Molecular Biology of the Cell( Garland Science 2008)
Binding of signal molecule
Most signal moleculesare hydrophilic
Some small signalmolecules diffuseacross target cell
membrane.
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Cell Communication
There are four basicmechanisms forcellular
communication:1. direct contact
2. paracrine signaling
3. synaptic signaling4. endocrine signaling
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Cell Communication
Direct contact molecules on the surfaceof one cell are recognized by receptors onthe adjacent cell
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Cell Communication
Paracrine signaling signal released froma cell has an effect on neighboring cells
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Cell Communication
Endocrine signaling hormones releasedfrom a cell affect other cells throughout thebody
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Cell Communication
Synaptic signaling nerve cells releasethe signal (neurotransmitter) which bindsto receptors on nearby cells
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Cell Communication
When a ligand binds to a receptor protein,the cell has a response.
signal transduction: the events within thecell that occur in response to a signal
Different cell types can respond differently tothe same signal.
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Cell Communication
A cells response to a signal often involves
activating or inactivating proteins.
Phosphorylation is a common way tochange the activity of a protein.
protein kinase an enzyme that adds aphosphate to a protein
phosphatase an enzyme that removes aphosphate from a protein
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Receptor Types
Receptors can be defined by their location.
intracellular receptor located within thecell
cell surface receptoror membranereceptor located on the plasmamembrane to bind a ligand outside the cell
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Receptor Types
There are 3 subclasses of membranereceptors:
1. channel linked receptors ion channel
that opens in response to a ligand2. enzymatic receptors receptor is an
enzyme that is activated by the ligand
3. G protein-coupled receptor a G-protein (bound to GTP) assists intransmitting the signal
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Intracellular Receptors
steroid hormones
-have a nonpolar, lipid-soluble structure
-can cross the plasma membrane to asteroid receptor
-usually affect regulation of gene expression
An inhibitor blocks the receptor from bindingto DNA until the hormone is present.
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Intracellular Receptors
A steroid receptor has 3 functional domains:
1. hormone-binding domain2. DNA binding domain
3. domain that interacts with coactivators to
affect gene expression
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Receptor Kinases
receptor tyrosine kinases
-membrane receptor
-when bound by a ligand, the receptor isactivated by dimerization andautophosphorylation
-activated receptor adds a phosphate totyrosine on a response protein
-an example is the insulin receptor
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Receptor Kinases
kinase cascade a series of proteinkinases that phosphorylate each other insuccession
-amplifies the signal because a few signalmolecules can elicit a large cell response
mitogen-activated protein (MAP) kinasesare activated by kinase cascades
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G-Protein Coupled Receptors
G-protein protein bound to GTP
G-protein-coupled receptor (GPCRs)receptors bound to G proteins
-G-protein is a switch turned on by thereceptor
-G-protein then activates an effector protein(usually an enzyme)
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G-Protein Coupled Receptors
Once activated, the effector proteinproduces a second messenger.
-second messenger generates the cellular
response to the original signalFor example one common effector protein
is adenylyl cyclase which produces
cAMP as a second messenger.Other second messengers: inositolphosphates, calcium ions (Ca2+)
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Cell-to-Cell Interactions
Cells can identify each other by cell surfacemarkers.
-glycolipids are commonly used as tissue-specific markers
-major histocompatibility complex (MHC)proteins are used by cells to distinguish
self from non-self
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Cell-to-Cell Interactions
Cells within a tissue are connected to eachother by cell junctions
1. tight junctions create sheets of cells
2. anchoring junctions connect thecytoskeletons of adjacent cells
3. communicating junctions permit smallmolecules to pass between cells
a. gap junctions in animal cells
b. plasmodesmata in plant cells
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