cell communication.pdf

8/13/2019 cell communication.pdf

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Cell Communication

Wednesday, June 1, 2011


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Cell Communication

Communication between cells requires:



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Cell Communication




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Cell Communication


ligand: the signaling molecule



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receptor protein: the molecule to which the

receptor binds



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receptor protein: the molecule to which thereceptor 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)



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Cell Communication



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Cell Communication

There are four basic mechanisms for cellularcommunication:



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1. direct contact



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1. direct contact

2. paracrine signaling



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1. direct contact


3. endocrine signaling



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Cell Communication


1. direct contact


3. endocrine signaling

4. synaptic signaling



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Direct contact molecules on the surfaceof one cell are recognized by receptors onthe adjacent cell



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Figure 15-4a Molecular Biology of the Cell( Garland Science 2008)



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Paracrine signaling signal released froma cell has an effect on neighboring cells



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Endocrine signaling hormones releasedfrom a cell affect other cells throughout thebody



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Synaptic signaling nerve cells releasethe signal (neurotransmitter) which bindsto receptors on nearby cells



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Cell Communication



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When a ligand binds to a receptor protein,the cell has a response.



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signal transduction: the events within thecell that occur in response to a signal



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Different cell types can respond differently tothe same signal.



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Cells respond to specific combinations of extracellular signals


iff f ll d diff l h


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Different types of cells respond differently to the same

extracellular signal molecule



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Figure 15-9b Molecular Biology of the Cell( Garland Science 2008)



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Figure 15-9c Molecular Biology of the Cell( Garland Science 2008)



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Figure 15-9d Molecular Biology of the Cell( Garland Science 2008)



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A cells response to a signal often involvesactivating or inactivating proteins.



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Phosphorylation is a common way to

change the activity of a protein.


C ll C i i


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change the activity of a protein.protein kinase an enzyme that adds a

phosphate to a protein


C ll C i ti


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change the activity of a protein.protein kinase an enzyme that adds a

phosphate to a protein

phosphatase an enzyme that removes aphosphate from a protein



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R t T


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Receptor Types


R t T


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Receptor Types

Receptors can be defined by their location.


R t T


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Receptor Types



Receptor Types


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Receptor Types


intracellular receptor located within the

cell


Receptor Types


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Receptor Types



cell


Receptor Types


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Receptor Types



cell

cell surface receptoror membrane

receptor located on the plasmamembrane to bind a ligand outside the cell


Intracellular Receptors


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steroid hormones




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steroid hormones

-have a nonpolar, lipid-soluble structure




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steroid hormones


-can cross the plasma membrane to a

steroid receptor




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steroid hormones



steroid receptor-usually affect regulation of gene expression




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steroid hormones







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steroid hormones




An inhibitor blocks the receptor from bindingto DNA until the hormone is present.



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A steroid receptor has 3 functional domains:




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1. hormone-binding domain




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2. DNA binding domain




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2. DNA binding domain

3. domain that interacts with coactivators toaffect gene expression



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Receptor Types


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p yp


Receptor Types


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p yp

There are 3 subclasses of membranereceptors:


Receptor Types


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p yp


1. channel linked receptors ion channel

that opens in response to a ligand


Receptor Types


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p yp



that opens in response to a ligand2. enzymatic receptors receptor is anenzyme that is activated by the ligand


Receptor Types


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p yp



that opens in response to a ligand2. enzymatic receptors receptor is anenzyme 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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Receptor Kinases


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Receptor Kinases


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receptor tyrosine kinases


Receptor Kinases


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receptor tyrosine kinases-membrane receptor


Receptor Kinases


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-when bound by a ligand, the receptor is

activated by dimerization andautophosphorylation


Receptor Kinases


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-activated receptor adds a phosphate to

tyrosine on a response protein


Receptor Kinases


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-activated receptor adds a phosphate to

tyrosine on a response protein-an example is the insulin receptor



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Receptor Kinases


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Receptor Kinases


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kinase cascade a series of proteinkinases that phosphorylate each other insuccession


Receptor Kinases


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-amplifies the signal because a few signalmolecules can elicit a large cell response


Receptor Kinases


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Receptor Kinases


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mitogen-activated protein (MAP) kinasesare activated by kinase cascades



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G-Protein Coupled Receptors


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G-protein protein bound to GTP




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G-protein protein bound to GTPG-protein-coupled receptor (GPCRs)

receptors bound to G proteins




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G-protein protein bound to GTPG-protein-coupled receptor (GPCRs)

receptors bound to G proteins

-G-protein is a switch turned on by thereceptor



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Once activated, the effector proteinproduces a second messenger.




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-second messenger generates the cellularresponse to the original signal




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For example one common effector proteinis adenylyl cyclasewhich producescAMP as a second messenger.




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For example one common effector proteinis adenylyl cyclasewhich producescAMP as a second messenger.

Other second messengers: inositolphosphates, calcium ions (Ca2+)



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Cell-to-Cell Interactions


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Cells can identify each other by cell surfacemarkers.




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-glycolipids are commonly used as tissue-

specific markers




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-glycolipids are commonly used as tissue-

specific markers-major histocompatibility complex (MHC)proteins are used by cells to distinguishself from non-self




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Cells within a tissue are connected to eachother by cell junctions




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1. tight junctions create sheets of cells




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2. anchoring junctions connect thecytoskeletons of adjacent cells




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3. communicating junctions permit smallmolecules to pass between cells




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a. gap junctions in animal cells




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a. gap junctions in animal cells

b. plasmodesmata in plant cells



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