SIGNAL TRANSDUCTIONSIGNAL TRANSDUCTION
IRAWAN YUSUFDepartment of Physiology
Faculty of Medicine Hasanuddin University
Makassar
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INTRODUCTIONINTRODUCTION
WHAT IS IT ?Signal transduction is a series of steps by which external stimuli are converted into chemical signals and than into cellular responses. A hormone or neurotransmitter binds to a specific receptor in the cell wall. This stimulates cell to produce second messengers which relay the hormonal signal to intracellular sites triggering the cell’s various responses.
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INTRODUCTIONINTRODUCTION
WHAT HAPPENS? A signal transduction pathway can be divided into three nain steps
Perception – perception of the environment Transduction – the first messenger trigger the
increase of second messenger Induction – the cellular response to the stimulus
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INTRODUCTIONINTRODUCTION
Cells communicate with each other via chemical messengers Signal transduction.
There are three general types of intercellular communication:– Paracrine communication– Autocrine communication– Endocrine communication
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The Component of Signal TransductionsThe Component of Signal Transductions
Ligands (hormones, neurotransmitters, drugs)
ReceptorsSecond MessengersEffectors
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Structure and function of receptorsStructure and function of receptors Chemical MessengersChemical Messengers
Neurotransmitters: Chemicals released from Neurotransmitters: Chemicals released from nerve endings which travel across a nerve nerve endings which travel across a nerve synapse to bind with receptors on target cells, synapse to bind with receptors on target cells, such as muscle cells or another nerve. Usually such as muscle cells or another nerve. Usually short lived and responsible for messages short lived and responsible for messages between individual cellsbetween individual cells
Hormones: Chemicals released from cells or Hormones: Chemicals released from cells or glands and which travel some distance to bind glands and which travel some distance to bind with receptors on target cells throughout the with receptors on target cells throughout the bodybody
Chemical messengers ‘switch on’ receptors Chemical messengers ‘switch on’ receptors without undergoing a reactionwithout undergoing a reaction
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Nerve 1
Nerve 2
Hormone
Bloodsupply
Neurotransmitters
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Receptors for LigandsReceptors for Ligands
Many of the receptors for chemical messengers have now been isolated and characterized
There are three types of receptor; membrane receptor, cytoplasmic receptor and nuclear receptor
Their propertis change quantitatively (down-regulation or up-regulation) or qualitatively (desensitization or hypersensitization) with changes in physiologic conditions
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Second MessengerSecond Messenger
Molecules that transmit and amplify signal Several second messengers have now been
isolated and characterized– cAMP (cyclic adenosine monophosphate)– cGMP (cyclic guanosine monophosphate)
– IP3 (inositol triphosphate)
– DAG (diacylgliserol)– Ca2+
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EffectorsEffectors
Molecules affected by second messengers Effectors affected by second messenger through
phosphorylation or transcription Effectors concits of:
– Ion channels– Genes– Enzymes
M
Gs ACGi
ATP cAMP PKAphosphorylation
Ca2+ ChannelK+ Channel ACh NE
PS S
(-)
3,5-AMP
PDE
AC, adenylate cyclase enzymeACh, acetylcholine3,5-AMP, 3,5-adenin monophosphateATP, adenin triphosphatecAMP, cyclic adenin monophosphateGi, G protein inhibitoryGs, G protein stimulatoryNE, norepinephrinePDE, phosphodiesterase enzymePKA, protein kinase A Gene transcriptions
NMDA
Ca2+
Ca2+ ChannelNa+ Channel
G l u t a m a t e
NK1
Subs P
PKC
PKA
IP3
AMPA
(Phosphorylation)
(Phosphorylation)
C-fibers terminal
Cornu Posterior Axon
Na+
Dark state Light state
Mechanism of Light ExcitationMechanism of Light Excitation
Mechanism of Light ExcitationMechanism of Light Excitation