Cel Communication

8/3/2019 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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