ap bio power point ch. 11

7/24/2019 ap bio power point ch. 11

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Evolution of Cell Signaling

A signal transduction pathway is a series ofsteps by which a signal on a cells surface isconverted into a specific cellular response


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Local and Long-Distance Signaling

Cells in a multicellular organism communicateby chemical messengers

Animal and plant cells have cell junctions that

directly connect the cytoplasm of adjacent cells

In local signaling, animal cells may

communicate by direct contact, or cell-cell

recognition

Copyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings


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Fig !!-"

Plasma membranes

Gap junctionsbetween animal cells

(a) Cell junctions

Plasmodesmatabetween plant cells

(b) Cell-cell recognition


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In many other cases, animal cells communicateusing local regulators, messenger molecules

that travel only short distances

In long-distance signaling, plants and animalsuse hormones



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Fig !!-#

Local signaling

Target cell

Secretingcell

Secretoryvesicle

Local regulator

diuses through

e!tracellular luid

(a) Paracrine signaling (b) Synaptic signaling

Target cell

is stimulated

"eurotransmitter

diuses across

synapse

#lectrical signal

along nerve cell

triggers release o

neurotransmitter

Long-distance signaling

#ndocrine cell $loodvessel

%ormone travelsin bloodstreamto target cells

Targetcell

(c) %ormonal signaling


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The Three Stages of Cell Signaling:A Preview

Cells receiving signals go through threeprocesses$

&eception

Transduction &esponse



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Fig !!-%-!

&eception'

#T&C#LL*L&+L*,

Signalingmolecule

Plasma membrane

C.T/PLS0

'

&eceptor


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Fig !!-%-&

'

#T&C#LL*L&+L*,

Signalingmolecule

Plasma membrane

C.T/PLS0

Transduction1

&elay molecules in a signal transduction pathway

&eception'

&eceptor


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Fig !!-%-'

#T&C#LL*L&+L*,

Plasma membrane

C.T/PLS0

&eceptor

Signalingmolecule

&elay molecules in a signal transduction pathway

ctivationo cellularresponse

Transduction &esponse1 2&eception'


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https$((wwwyoutubecom(watch)v*+dn!./01A


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Reception: A signal molecule binds to a receptorprotein, causing it to change shape

2he binding between a signal molecule3ligand4 and receptor is highly specific

A shape change in a receptor is often the initial

transduction of the signal

5ost signal receptors are plasma membrane

proteins


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Receptors in the lasma !embrane

2here are three main types of membranereceptors$

6 protein-coupled receptors

7eceptor tyrosine 8inases Ion channel receptors


!!


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Fig !!-9b

G protein-coupledreceptor

Plasmamembrane

#n3ymeG protein(inactive)

GP

C.T/PLS0

ctivateden3yme

GTP

Cellular response

GP

P i

ctivatedreceptor

GP GTP

Signaling molecule,nactiveen3yme

' 1

2 4


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Fi !! 9d


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Fig !!-9d

Signaling

molecule

(ligand)

Gateclosed ,ons

Ligand-gatedion channel receptor

Plasmamembrane

Gate open

Cellularresponse

Gate closed2

1

'


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"ntracellular Receptors

:ome receptor proteins are intracellular, foundin the cytosol or nucleus of target cells

:mall or hydrophobic chemical messengers

can readily cross the membrane and activatereceptors

;+amples of hydrophobic messengers are the

steroid and thyroid hormones of animals


Fig !! < !


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Fig !!-


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Fig !!-


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Fig !!-


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Fig !!-


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http$((bcswhfreemancom(thelifewire(content(chp!#(!#=&=html


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Transduction: Cascades of molecular interactionsrela# signals from receptors to target molecules in

the cell :ignal transduction usually involves multiple

steps

5ultistep pathways can amplify a signal$ A fewmolecules can produce a large cellular

response

5ultistep pathways provide more opportunitiesfor coordination and regulation of the cellular

response


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rotein hosphor#lation and Dephosphor#lation

In many pathways, the signal is transmitted by acascade of protein phosphorylations

Protein 5inases transfer phosphates from A2 to

protein, a process called phosphorylation

Protein phosphatases remove the phosphates

from proteins, a process called dephosphorylation

2his phosphorylation and dephosphorylationsystem acts as a molecular switch, turning

activities on and off


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Small !olecules and "ons as Second !essengers

2he e+tracellular signal molecule that binds tothe receptor is a pathways >first messenger?

Second messengers are small, nonprotein,

water-soluble molecules or ions that spreadthroughout a cell by diffusion

Cyclic A5 and calcium ions are common

second messengers

Fig !!-!!
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+irst messenger

Fig !! !!

G protein

denylyl

cyclase

GTP

TP

c0PSecondmessenger

Protein5inase

G protein-coupled

receptor

Cellular responses


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Response: Cell signaling leads to regulation oftranscription or c#toplasmic activities



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$uclear and C#toplasmic Responses

/ltimately, a signal transduction pathway leadsto regulation of one or more cellular activities

regulation of a cytosolic en0yme

! @r

7egulation of a gene


Fig !!-!#


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g

&eception

Transduction

&esponse

$inding o epinephrine to G protein-coupled receptor (' molecule)

,nactive G protein

ctive G protein ('61molecules)

,nactive adenylyl cyclase

ctive adenylyl cyclase ('61)

TP

Cyclic 0P ('64)

,nactive protein 5inase

ctive protein 5inase ('64)

,nactive phosphorylase 5inase

ctive phosphorylase 5inase ('67)

,nactive glycogen phosphorylase

ctive glycogen phosphorylase ('68)

Glycogen

Glucose-'-phosphate

('69

molecules)


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%ine-Tuning of the Response

5ultistep pathways have two importantbenefits$

Amplifying the signal 3and thus the response4

! At each step, the number of activatedproducts is much greater than in the

preceding step

Contributing to the specificity of the response! ;ach step is specific- remember the

specificity of each en0yme for its substrate



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The Specificity of Cell Signaling and Coordinationof the Response

ifferent 8inds of cells have different collections ofproteins

ifferent A e+pressed in different types of

cells

2hese different proteins allow cells to detect and

respond to different signals

;ven the same signal can have different effects incells with different proteins and pathways

athway branching and >cross-tal8? further help

the cell coordinate incoming signalsCopyright 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings


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Signaling Efficiency: Scaffolding Proteins andSignaling Complexes

Scaolding proteins are large relay proteinsto which other relay proteins are attached

:caffolding proteins can increase the signal

transduction efficiency by grouping togetherdifferent proteins involved in the same pathway


Fig !!-!


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Signalingmolecule

&eceptor

Scaoldingprotein

Plasmamembrane

Threedierentprotein

5inases


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Termination of the Signal

Inactivation mechanisms are an essentialaspect of cell signaling

Bhen signal molecules leave the receptor, the

receptor reverts to its inactive state


A t i d ll d th


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Apoptosis- programmed cell death


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Apoptosis &programmed cell death' integratesmultiple cell-signaling path(a#s

poptosis is programmed or controlled cellsuicide

A cell is chopped and pac8aged into vesicles

that are digested by scavenger cells

Apoptosis prevents en0ymes from lea8ing out

of a dying cell and damaging neighboring cells


Fig !!-!


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1 :m

;+tracellular signals result in formation of blebs


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Apoptotic ath(a#s and the Signals That TriggerThem

Apoptosis can be triggered by$ An e+tracellular death-signaling ligand

A damage in the nucleus

rotein misfolding in the endoplasmicreticulum

Apoptosis may be involved in some diseases

3for e+ample, ar8insons and Al0heimers4Dinterference with apoptosis may contribute to

some cancers

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ap bio power point ch. 11