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Intercellular Communication
&
Signal Transduction Mechanism
Department of Physiology
School of Medicine
University of Sumatera Utara
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Intercellular Communication
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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Intercellular Communication
and Signal Transduction
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.
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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
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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The endocrine system
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 endocrine system
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.
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The endocrine system
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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The endocrine system
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Intercellular Communication
and Signal Transduction
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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Signal Transduction in Cells
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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Signal Transduction in Cells
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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Signal Transduction in Cells
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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Signal Transduction in Cells
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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Signal Transduction in Cells
Activation and Inactivation of the G Protein
2.The receptor with bound hormone activates
the G protein and replaces GDP...
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Signal Transduction in Cells
Activation and Inactivation of the G Protein
3....with GTP and the G proteins is
activated. The subunits separate.
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Signal Transduction in Cells
Activation and Inactivation of the G Protein
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
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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
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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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