cell signaling a __________________________is a series of steps by which a signal on a cell’s...
TRANSCRIPT
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Cell Signaling• A __________________________is a series of steps by
which a signal on a cell’s surface is converted into a ________________________________________________
• Signal transduction pathways convert _________________ on a cell’s surface into _____________________________
AP Biology
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Minzenmayer AP Biology Sig
nal
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h _
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Local vs. Long Distance Signaling
•Animal cells communicate using _____________________.•messenger molecules that travel only short distances
•long-distance signaling•plants and animals use chemicals called ____________________.
AP Biology
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Minzenmayer AP Biology
e.g., interferon release by viral-infected cells
Local Signaling w/o ____________________
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Minzenmayer AP Biology ____
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Sig
nalin
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AP Biology Lo
ng
-Dis
tan
ce _
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_ Note how specificity is determined by presence/absence of receptor protein
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AP Biology
___________________________________
In this case the receptor protein is a membrane proteinLigan
d
Often turning on or off enzyme
activity
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Wrap-Up
•How are receptor ligand interactions similar to enzyme substrate interactions?
AP Biology
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Warm Up
AP Biology
In picture A, label the following:-cell-ligand-receptor-membrane channel
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Warm Up
AP Biology
Which diagram depicts communication between cells that are in close proximity?
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Warm Up
AP Biology
Which diagram depicts long distance communication between cells?
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Warm Up
AP Biology
In which type of communication would the ligand need to have the longest “life”?
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What’s the point of Cell Communication??
Examples:• Epinephrine stimulates the breakdown of glycogen in
mammals• Temperature determines sex of some vertebrate
organisms• DNA repair mechanisms
AP Biology
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AP Biology
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Receptors in Plasma Membrane• three main types of membrane receptors:
• _______________________________________________
• _______________________________________________
• _______________________________________________
AP Biology
STEP 1: __________________________
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____________________________________•G protein-coupled receptor
• plasma membrane receptor that works with the help of a G protein
•G protein acts as an on/off switch: • If GDP is bound to the G protein, G protein is
_____________________
AP Biology
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Minzenmayer AP Biology ____
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G proteins bind GTP
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Fig. 11-7b
G protein-coupledreceptor
Plasmamembrane
Enzyme
G protein(inactive)
GDP
CYTOPLASM
Activatedenzyme
GTP
Cellular response
GDP
Pi
Activatedreceptor
GDP GTP
Signaling molecule
Inactiveenzyme
1 2
3
4
G-Protein-Linked ReceptorThe more __________ binding, the greater the cellular response
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Tyrosine Kinases•Receptor tyrosine kinases
• membrane receptors that attach _________________ to tyrosines
• can trigger multiple signal transduction pathways at once
AP Biology
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AP Biology Pro
tein
Kin
ase
& P
ho
sph
atas
e
P r o te in O H + A T P P r o te in O P
O
O
O
+ A D P
P i H 2 O
P r o te in K in a s e
P r o te in P h o s p h a t a s e
reversibility of phosphorylation makes
signaling reversible
responses tend to continue (or
expand) only so long as signaling
continues
reversibility contributes to the dynamic nature of
cells
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Minzenmayer AP Biology
Tyrosine Kinase Receptor
Liga
nd R
ecep
tion
Rece
ptor
dim
eriz
ation
Phos
phor
yliz
ation
Protein
Activation
Tran
sduc
tion
Resp
onse
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Ligand Gated Ion Channel
•ligand-gated ion channel receptor •acts as gate when __________________________ changes _______________.
•When signal molecule binds as a ligand to receptor, gate allows specific ions, such as Na+ or Ca2+, through a channel in receptor
AP Biology
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Minzenmayer AP Biology
Ion
-Ch
ann
el R
ecep
tor
Reversibility is assured by
pumping ions back out again (using separate
protein)
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AP Biology
Wrap-UpWould a hydrophobic molecule be expected to have an internal
or membrane receptor?
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Intracellular Receptors• Some receptor proteins are intracellular
• found in ________________ or _________________of target cells
• Examples of messengers • steroid and thyroid _______________________ of animals
• An activated hormone-receptor complex can act as a _____________________________________________• turning on specific ____________________
AP Biology
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Minzenmayer AP Biology
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Transduction•molecules that relay a signal from receptor to response are mostly ________________________.
•Like falling dominoes, receptor activates another protein, which activates another, …..until protein producing response is activated
•At each step, signal is _____________________ into a different form, usually a __________________ change in a protein
AP Biology
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Protein Phosphorylation & Dephosphorylation
• In many pathways, signal is transmitted by cascade of protein ___________________________.
• Protein ____________________ transfer phosphates from ATP to protein, a process called ________________________________.
• Protein ____________________________ remove phosphates from proteins, a process called _____________________________.
• phosphorylation and dephosphorylation system acts as molecular switch, turning activities on and off
AP Biology
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Signaling molecule
Receptor Activated relaymolecule
Inactiveprotein kinase1
Activeproteinkinase1
Inactiveprotein kinase2
ATPADP
Activeproteinkinase2
P
PPP
Inactiveprotein kinase3
ATPADP Active
proteinkinase3
P
PPP
i
ATPADP P
ActiveproteinPP
P i
Inactiveprotein
Cellularresponse
Phosphorylation cascade
i
______________________ Cascade
Activates protein kinase
Active PK1 transfers PFrom ATP to inactive PK2
Protein phosphatases (PP) catalyze removal of P to make them inactive again
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Small Molecules & Ions Second Messengers• extracellular signal molecule that binds to receptor is a pathway’s
“___________________________________”
• _________________________________are
• small, nonprotein, water-soluble molecules or
• ions that spread throughout a cell by ____________________
• participate in pathways initiated by G protein-coupled receptors and receptor tyrosine kinases
• _____________________and __________________ ions are common second messengers
AP Biology
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Cyclic AMP
•cAMP •widely used _________________________ messengers
•Adenylyl cyclase•converts _________________ to ________________ in response to extracellular signal
AP Biology
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cAMP• Many signal molecules trigger formation of cAMP
• Other components of cAMP pathways are • ________________________
• G protein-coupled receptors
• ____________________________________
• cAMP usually activates protein kinase A, which phosphorylates various other proteins
• Further regulation of cell metabolism is provided by G-protein systems that inhibit adenylyl cyclase
AP Biology
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First messengerFig. 11-11
G protein
Adenylylcyclase
GTP
ATP
cAMPSecondmessenger
Proteinkinase A
G protein-coupledreceptor
Cellular responses
cAM
P a
s a
____
____
____
_
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Cell Signaling - Disease • Cholera
• Caused by Vibrio cholerae in contaminated water• Toxin secreted by V. cholerae in small intestine• Toxin modifies ______________________involved in salt/water
secretion • Can no longer hydrolyze GTP• Always __________________ - stimulates cAMP production
• Intestinal cells secrete water/ions• Severe diarrhea
• often lethal due to dehydration and salt imbalance
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Cell Signaling - Cholera
H2O, ions
H2O, ionsGDPGTP
Toxinactive inactive
Intestinal Cell
Ext
Int
Net Effect
Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings
cAMP
Intestinal Lumen
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Calcium Ions & Inositol Triphosphate (IP3)
•Calcium ions (Ca2+) •act as a second messenger in many pathways
•Calcium is an important second messenger because cells can regulate its concentration
AP Biology
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Nuclear & Cytoplasmic Responses• signal transduction pathway leads to
__________________ of one or more cellular activities• response may occur in
• cytoplasm or • may involve action in nucleus
• Many signaling pathways regulate synthesis of _________________• usually by turning genes on or off in nucleus
• final activated molecule may function as _________________________________
AP Biology
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Fig. 11-14
Growth factor
Receptor
Phosphorylationcascade
Activetranscriptionfactor
P
Inactivetranscriptionfactor
CYTOPLASM
DNA
NUCLEUS mRNA
GeneNu
clea
r R
esp
on
se
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Fine Tuning Response
•Multistep pathways have two important benefits:• _________________________ signal
• and therefore the response• Contributing to ____________________ of response
•Signal Amplification• Enzyme cascades amplify cell’s response• At each step, number of activated products is much
greater than in preceding stepAP Biology
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Minzenmayer AP Biology Sig
nal
Am
plif
icat
ion
(C
asca
de)
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Minzenmayer AP Biology Sig
nal
Am
plif
icat
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(C
asca
de)
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WRAP-UP