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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
Minzenmayer AP Biology Sig
nal
ing
wit
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
Minzenmayer AP Biology
e.g., interferon release by viral-infected cells
Local Signaling w/o ____________________
Minzenmayer AP Biology ____
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Sig
nalin
g
AP Biology Lo
ng
-Dis
tan
ce _
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_ Note how specificity is determined by presence/absence of receptor protein
AP Biology
___________________________________
In this case the receptor protein is a membrane proteinLigan
d
Often turning on or off enzyme
activity
Wrap-Up
•How are receptor ligand interactions similar to enzyme substrate interactions?
AP Biology
Warm Up
AP Biology
In picture A, label the following:-cell-ligand-receptor-membrane channel
Warm Up
AP Biology
Which diagram depicts communication between cells that are in close proximity?
Warm Up
AP Biology
Which diagram depicts long distance communication between cells?
Warm Up
AP Biology
In which type of communication would the ligand need to have the longest “life”?
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
AP Biology
Receptors in Plasma Membrane• three main types of membrane receptors:
• _______________________________________________
• _______________________________________________
• _______________________________________________
AP Biology
STEP 1: __________________________
____________________________________•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
Minzenmayer AP Biology ____
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G proteins bind GTP
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
Tyrosine Kinases•Receptor tyrosine kinases
• membrane receptors that attach _________________ to tyrosines
• can trigger multiple signal transduction pathways at once
AP Biology
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
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
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
Minzenmayer AP Biology
Ion
-Ch
ann
el R
ecep
tor
Reversibility is assured by
pumping ions back out again (using separate
protein)
AP Biology
Wrap-UpWould a hydrophobic molecule be expected to have an internal
or membrane receptor?
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
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
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
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
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
Cyclic AMP
•cAMP •widely used _________________________ messengers
•Adenylyl cyclase•converts _________________ to ________________ in response to extracellular signal
AP Biology
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
First messengerFig. 11-11
G protein
Adenylylcyclase
GTP
ATP
cAMPSecondmessenger
Proteinkinase A
G protein-coupledreceptor
Cellular responses
cAM
P a
s a
____
____
____
_
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
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
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
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
Fig. 11-14
Growth factor
Receptor
Phosphorylationcascade
Activetranscriptionfactor
P
Inactivetranscriptionfactor
CYTOPLASM
DNA
NUCLEUS mRNA
GeneNu
clea
r R
esp
on
se
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
Minzenmayer AP Biology Sig
nal
Am
plif
icat
ion
(C
asca
de)
Minzenmayer AP Biology Sig
nal
Am
plif
icat
ion
(C
asca
de)
WRAP-UP