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Cellular and Molecular Biology > Final: Ch 15 G-Protein Coupled Receptors > Flashcards

Final: Ch 15 G-Protein Coupled Receptors Flashcards

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1
Q

what is a G-protein

A

GTP-binding protein

bind GTP/GDP

active when bound to GTP, inactive when bound to GDP

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2
Q

regulation of G-protein genes

A

transcriptional regulation using TF (binds to promoter)

post-translational regulation/modification

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3
Q

examples of post-transcriptional regulation of G-protein genes

A

alternative splicing

capping

polyadenylation

RNAi

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4
Q

G-proteins are anchored in the cell membrane when…

A

GDP bound –> ligand binds –> GTP binds to alpha subunit

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5
Q

4 things GPCR signal transduction pathways have in common

A

receptor with 7 transmembrane alpha helices

coupled trimeric G-protein switch

membrane-bound effector protein

proteins for feedback regulation and desensitization of the pathway

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6
Q

where are the N and C termini of GPCR

A

N-terminus on extracellular face

C-terminus on cytosolic face

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7
Q

B-adrenergic receptors

A

bind hormones like epi and nor-epi

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8
Q

can different subtypes of GPCR bind the same hormone and have different effects?

A

yes

ex. epinepherine (in heart increases contraction, in smooth muscle relaxes)

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9
Q

what happens in fight or flight

A

adrenal gland releases Epi to bind B-adrenergic GPCR in liver/muscle cells

stimulate glycogen breakdown to glucose

high epi in blood

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10
Q

trimeric G-proteins 3 subunits

A

alpha

beta + gamma (complexed together)

linked to membrane by lipids

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11
Q

in resting state, G-alpha subunit has a bound ___ and is complexed to _____

A

GDP, complexed to G-betagamma

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12
Q

binding of ligand to GPCR changes conformation of the receptor and allows…

A

the receptor to bind to G-alpha subunit –> release GDP

GTP binds G-alpha –> release of receptor and G-betagamma

G-alpha binds effector protein

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13
Q

how to detect GPCR-mediated dissociation of the G protein

A

FRET - fluorescence energy transfer

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14
Q

all effector proteins in GPCR pathway are either…

A

membrane bound ion channels

membrane bound enzymes that catalyze formation of 2nd messengers

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15
Q

which subunit of the G-protein determines its function?

A

G-alpha

ex. G-alpha S activates adenylyl cyclase to increase cAMP

G-alpha i inhibits adenylyl cyclase to decrease cAMP

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16
Q

one of the simplest cellular responses to a signal is the opening of…

A

ion channels

ex. open ligand-gated ion channels for neurotransmitters

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17
Q

many nt receptors are…

A

GPCR whose effector proteins are Na or K channels

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18
Q

mAChR are a type of GPCR found in _____ muscle

A

cardiac muscle

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19
Q

what happens when mAChR are activated

A

G-betagamma opens K+ channel (usually G-alpha)

slow heart rate when K+ channels open

efflux of K+ causes hyperpolarization and slows contraction

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20
Q

cones are for ____, rods are for ____/______

A

color, black/white

found in retina, signals processed by visual cortex

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21
Q

rhodopsin

A

light-sensitive GPCR (opsin) that helps rods sense light

G-protein called Transducin (G-alpha-t)

photon-absorbing pigment called retinal

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22
Q

how does rhodopsin differ from other GPCRs

A

absorption of a photon of light is the signal (by retinal), not binding of ligand

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23
Q

what happens when rhodopsin absorbs a photon of light

A

cis –> trans in retinal form causes conformational change in GPCR opsin

rhodopsin binds G-alpha-t subunit and exchanges GDP for GTP

G-alpha-t removes inhibitory gamma segments from phosphodiesterase (PDE), which turns cGMP –> GMP

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24
Q

activation of rhodopsin by light leads to the closing of ____-gated cation channels

A

cGMP

causes membrane potential to become more inside negative (hyperpolarization-less nt released)

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25
in the dark the membrane potential of a rod cell is...
-30mV this is a state of depolarization so in the dark, the rod cell is constantly secreting nt
26
why is there a constant state of depolarization of resting rod cells
large number of open nonselective ion channels that let Na and Ca in
27
to close the cation channels, the 2nd messenger _____ is turned into
cGMP --> GMP upon absorbing light, cGMP PDE hydrolyzes cGMP to GMP cGMP releases from gated channels, closing them
28
the ____ level of cGMP in the dark keeps cGMP gated cation channels open, in the light...
high decrease in cGMP concentration by PDE causes closing of channels and less nt release
29
what makes the rhodopsin signal transduction pathway so sensitive?
signal amplification of the photon of light each activated opsin activates 500 G-alpha-t molecules which activate the PDE
30
what GAP proteins inactivate G-alpha-t GTP
RGS-9 and G-beta-5 hydrolyze GTP --> GDP so PDE is inactivated again
31
Rhodopsin kinase
phosphorylates active rhodopsin arrestin binds after 3 phosphates and prevents transducin activation (G-alpha-t)
32
how do rod cells adapt to varying levels of ambient light -- visual adaptation
adjusting trafficking of arrestin and transducin 80% of G-alpha-t and G-betagamma move out of the outer segment and 80% of arrestin moves into outer segment in 10 min of moderate light prevents PDE activation
33
adenylyl cyclase synthesizes ____ from ____
cAMP, ATP
34
cAMP activates a _____
kinase
35
glycogen
a storage polymer of glucose broken down in liver/muscle cells in response to the hormone epinerpherine
36
all of the effects of cAMP are mediated through activation of which kinase
protein kinase A (cAMP dependent protein kinase) binding of cAMP opens catalytic active site
37
degradation of glycogen is called
glycogenolysis stepwise removal of glucose residues from one end of the polymer by glycogen phosphorylase
38
in the liver, glycogen stores are broken down to ....
glucose, which is released into the blood and transported to tissues like muscle and brain for energy
39
2 ways epinerpherine stimulated activation of adenylyl cyclase --> higher cAMP --> PKA activation enhances conversion of glycogen to glucose
inhibit glycogen synthesis enzymes stimulating glycogen degradation enzymes
40
what does PKA do
phosphorylates and inactivates glycogen synthase (GS), the enzyme that synthesizes glycogen phosphorylates the inhibitor of phosphoprotein phosphatase (IP) to inactivate it (so glycogen phosphorylase kinase can break down glycogen)
41
in adipose cells, what does activation of PKA do
phosphorylation of a lipase that hydrolyzes stored triglycerides to FA and glycerol for energy
42
is there signal amplification in the cAMP-PKA pathway?
yes GPC hormone receptors are able to diffuse rapidly in the plasma membrane a single epinerpherine-GPCR complex activates up to 100 G-alpha s molecules --> adenylyl cyclase and so on
43
activation of PKA also stimulates the expression of...
many genes, including CREB leads to long-term effects
44
CRE
cAMP response element binds the phosphorylated form of the TF CREB
45
all genes regulated by PKA have ____
CRE binds the phosphorylated form of the TF CREB
46
CREB TF
CRE-binding protein found in nucleus
47
genomic response of PKA
catalytic subunit of PKA targets CREB in nucleus and phosphorylates it CREB binds to distal promoter (response element) of target gene and recruits co-regulator stimulates gene transcription
48
a ligand (hormone) can have a non ______ response, a ______ response, or both
genomic, genomic
49
what is A kinase-associated protein
an anchoring protein that binds PKA to specific locations so it is activated in only those locations ex. heart muscle cells have AKAP15 near Ca channels
50
AKAP in the outer nuclear membrane
localizes PKA and cAMP PDE to outer nuclear membrane helps catalytic subunits of PKA enter nucleus allows for negative feedback regulation
51
3 ways to down-regulate signaling through the GPCR/cAMP/PKA pathway
affinity of receptor for ligand is decreased when GDP is replaced by GTP in G-alpha intrinsic GTPase activity of G-alpha hydrolyzes GTP --> GDP (hydrolysis rate increased when G-alpha binds adenylyl cyclase) cAMP PDE hydrolyzes cAMP --> AMP to end cellular response
52
most GPCRs are also down-regulated by ______-_________
feedback repression end product blocks early step in pathway
53
B-arrestin
assists endocytosis of cell-surface receptors
54
phospholipase C (PLC)
enzymes that hydrolyze a phosphoester bond to yield 2nd messengers that raise cytosolic Ca2+ levels and remodel actin activate protein kinase C
55
protein kinase C (PKC)
affect cellular growth and differentiation
56
important 2nd messengers are derived from the membrane lipid, ______________
phosphatidylinositol (PI) PI --> PIP2
57
PLC cleaves PIP2 into...
DAG (diacylglycerol) and IP3 (inositol triphosphate)
58
DAG is associated with the ______ while IP3 freely _______ in the cytosol
membrane, diffuses
59
GPCR that activate PLC increase cytosolic ____ concentration even when the ions are absent from the extracellular fluid
Ca2+ concentration PLC cleaves PIP2 into IP3, which opens IP3 gated-Ca channel in ER lumen
60
what does DAG activate
protein kinase C - moves to cytosolic leaflet
61
activation of PKC has what effects
growth and metabolism phosphorylates TF ex. in liver cells, PKC regulates glycogen metabolism
62
calmodulin
small cytosolic switch protein that mediates many cellular effects of Ca ions
63
glycogen breakdown and synthesis is coordinately regulated by which two second messengers
Ca2+ and cAMP levels are regulated by neural and hormonal stimulation
64
why is nitroglycerin used to treat angina
decomposes to nitric oxide (NO), which relaxes smc in the heart
65
what is the allosteric effect (Hb) -- positive cooperativity
Hb binds oxygen -- increased affinity in lungs, less in tissue more binding increases affinity creates a more dramatic switch
66
basic epi GPCR pathway
epi + GPCR --> GTP G-alpha activate adenylyl cyclase --> higher cAMP cAMP activates PKA to stimulate breakdown of glycogen OR phosphorylation of TF in the nucleus (ex. CREB)
67
do G proteins usually have short-term or long-term effects?
short-term modify existing enzymes or ion channels
68
structure of inactive PKA
tetramer of 2 regulatory subunits and 2 catalytic subunits each R subunit binds the active site of a C subunit to inactivate
69
how is inactive PKA turned on
2 cAMP binds each R subunit conformational change causes R subunits to release C subunits
70
glycogen phosphorylase kinase
glycogen --> glucose activates glycogen phosphorylase activated by high [Ca2+], PKA
71
glycogen synthase
stimulates glycogen formation inhibited by PKA, PKC

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