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