BBS1 FL K7 Komunikasi Antar Sel

8/14/2019 BBS1 FL K7 Komunikasi Antar Sel

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Intercellular Communication

&

Signal Transduction Mechanism

Department of Physiology

School of Medicine

University of Sumatera Utara


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and Signal Transduction

The ability of cells to communicate with

each other is essential for coordination of

their diverse activities to maintain

homeostasis as well as to control growth and

development of the body as a whole


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These signals come from distant cells

(known as endocrine signals, like hormones

and growth factors); they come from

neighboring cells (known as paracrine

signals); they even come from within the

same cell (known as autocrine signals)


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Signaling Types

Local signaling

Gap junction

Paracrine--signaling that affects neighboring cells

Autocrine--secretion that affects same cell

Long Distance

Endocrine--secretion of a substance that is released

into the blood and affects a distant target


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Gap Junction

A g p junctionor nexusis a junctionbetween certain cell-types that allowsdifferent moleculesand ionsto pass freelybetween cells.

The junction connects the cytoplasmofcells. One gap junction is composed of twoconnexons(or hemichannels) which

connect across the intercellular space.
http://www.answers.com/topic/cellhttp://www.answers.com/topic/moleculehttp://www.answers.com/topic/ionhttp://www.answers.com/topic/cytoplasmhttp://www.answers.com/topic/connexonhttp://www.answers.com/topic/connexonhttp://www.answers.com/topic/cytoplasmhttp://www.answers.com/topic/ionhttp://www.answers.com/topic/moleculehttp://www.answers.com/topic/cell


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Gap JunctionAt gap junctions, the intercellular spaces narrows from 2nm to 3nm

and unit connexonsin the membrane of each cell are lined up with one

another
http://www.answers.com/topic/connexonhttp://www.answers.com/topic/connexonhttp://www.answers.com/main/Record2?a=NR&url=http%3A%2F%2Fcommons.wikimedia.org%2Fwiki%2FImage%3AGap%2520cell%2520junction.svg


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Gap Junction

Allows for chemical communicationbetween cells, through the transmission ofsmall second messengers, such as Ca++,although different connexin subunits canmake selectivity for particular small

molecules.

Generally allows molecules smaller than1,000 Daltons to pass through,


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Gap junctions are particularly important in

the cardiac muscle: the signal to contract is

passed efficiently through the gap junctions,

allowing the heart muscle cells to contract

in tandem.
http://www.answers.com/topic/hearthttp://www.answers.com/topic/heart


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ParacrineThe signal chemical is

called the paracrine agent.They are secreted into the

interstitial fluid and diffuse

to adjacent cells, where

they have their biologic

action


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Paracrine


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utocrineAutocrine is a form of hormonal

signalling in which a cell secretes a

hormone, or chemical messenger(called the autocrine agent) that binds

to autocrine receptors on the same cell,

leading to changes in the cell


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utocrine


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The endocrine system

The other communication system in the

body is made up of endocrine glandsthatproduce hormones, chemical substances

released into the bloodstream to guide such

processes as metabolism, growth, etc.


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The endocrine system is an information

signaling system much like the nervous

system. However, the nervous system uses

nerves to conduct information, whereas the

endocrine system uses blood vessels as

information channels


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Glands located in many regions of the bodyrelease into the bloodstream specific chemical

messengers called hormones, which regulate themany and varied functions of an organism.


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The typical endocrine organ is a ductless glandthat secretes chemical mediators directly into local

blood vessels which circulate within the body viathe bloodstream. These hormones travel to distant

organs to regulate the target organ's function.
http://k/wiki/Ductless_glandhttp://k/wiki/Bloodhttp://k/wiki/Bloodhttp://k/wiki/Ductless_gland


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Major endocrine glands. (Male left,

Female on the right.)

1. Pineal gland

2. Pituitary galnd3. Thyroid galnd

4. Thymus

5. Adrenal gland

6. Pancreas

7. Ovary

8. Testes


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Gap

junctions

Synaptic Paracrine &

Autocrine

Endocrine

Message

transmission

Directly

from cell

to cell

Across

synaptic

cleft

By diffusion

in interstitial

fluid

By

circulating

body fluids

Local or

general

Local Local Locally

diffused

General

Specificitydepends on

Anatomiclocation

Anatomiclocation &

receptors

Receptors Receptors


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Signal Transduction in Cells

Cells in our body are surrounded by a

lipid membrane. The "water-loving"

heads of the phospholipid molecules

(blue) are directed towards the outerand inner surfaces of the membrane.

Many proteins stretch through the entire

membrane.


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Extracellular signaling molecules(usually hormones, neurotransmitters,cytokines, growth factorsor cell

recognition molecules) attach to thereceptor, triggering changes in thefunction of the cell

The binding initiates a chemicalchange on the intracellularside of themembrane
http://en.wikipedia.org/wiki/Signaling_moleculehttp://en.wikipedia.org/wiki/Hormonehttp://en.wikipedia.org/wiki/Neurotransmittershttp://en.wikipedia.org/wiki/Cytokineshttp://en.wikipedia.org/wiki/Growth_factorshttp://en.wikipedia.org/wiki/Cell_adhesion_moleculehttp://en.wikipedia.org/wiki/Cell_adhesion_moleculehttp://en.wikipedia.org/wiki/Receptor_(biochemistry)http://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Intracellularhttp://en.wikipedia.org/wiki/Intracellularhttp://en.wikipedia.org/wiki/Cell_(biology)http://en.wikipedia.org/wiki/Receptor_(biochemistry)http://en.wikipedia.org/wiki/Cell_adhesion_moleculehttp://en.wikipedia.org/wiki/Cell_adhesion_moleculehttp://en.wikipedia.org/wiki/Growth_factorshttp://en.wikipedia.org/wiki/Cytokineshttp://en.wikipedia.org/wiki/Neurotransmittershttp://en.wikipedia.org/wiki/Hormonehttp://en.wikipedia.org/wiki/Signaling_molecule


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Extracellular signal molecule: an extracellular signalmolecule is produced by one cell and is capable of travelingto neighboring cells, or to cells that may be far away.

Receptor protein: the cells in an organism must have cellsurface receptor proteins that bind to the signal moleculeand communicate its presence inward into the cell.

Intracellular signaling proteins: these distribute the signal tothe appropriate parts of the cell. The binding of the signalmolecule to the receptor protein will activate intracellularsignaling proteins that initiate a signaling cascade (a seriesof intracellular signaling molecules that act sequentially).

Target proteins: the conformations or other properties of thetarget proteins are altered when a signaling pathway isactive and changes the behavior of the cell


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A first messenger (1), a molecule of adrenaline,

binds to a specific adrenaline receptor (2), a

discriminator. Thereby, the transducer (3), a G

protein - composed of alpha-, beta- and gamma

subunits - is activated, This, in turn, stimulates the

amplifier (4), adenylate cyclase, which produces (5)

the second messenger, cyclic AMP, from (6)ATP

(adenosine- triphosphate).

(7)A cascade of enzymatic reactions alters the

behaviour of the cell and (8)via phosphorylation (9)

glycogen is transformed to (10)glucose, which the

cell uses to generate ATP.

Phosphorylation can also alter membrane proteins,

for example, ion channels (11)


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Activation and Inactivation of the G Protein

1.The G protein, composed of alpha-, beta- and

gamma-subunits, in its resting state with bound GDP


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2.The receptor with bound hormone activates

the G protein and replaces GDP...


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3....with GTP and the G proteins is

activated. The subunits separate.


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4.Some seconds later the GTP, bound

to the alpha-subunit, is hydrolysed to

GDP. The subunits recombine.


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Membrane receptors

specialized integral membrane proteins

that take part in communication

between the cell and the outside world

play a unique and important role in

cellular communications and signal

transduction
http://en.wikipedia.org/wiki/Integral_membrane_proteinhttp://en.wikipedia.org/wiki/Integral_membrane_protein


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Membrane receptors

Membrane receptors generally function

by binding the signal, or ligand and

causing the production of a second

signal (second messenger) that causesa cellular response. The diagram shows

how the receptor for insulin functions.


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Membrane receptors
http://en.wikipedia.org/wiki/File:Transmembrane_receptor.svg


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A pair of insulin molecules bind toreceptors, causing a change in theprotein structure that exposes akinase or phosphate transferringenzyme inside the cell

The activated receptor kinasetransfers a phosphate group toadjacent receptor molecules,leading to the activation of

subcellular proteins and a cellularresponse to insulin

The receptors must be integralmembrane proteins that passthrough the lipid bilayer. Through

this system, an insulin molecule cancause a response inside the cellwithout passing through the lipidbilayer


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Cellular response


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