2.8: Signaling via Small Molecules Flashcards
state the three mechanisms of small molecule signaling
- independent on plasma membrane proteins
- through ions channels
- downstream of g-protein coupled receptors
give examples of small hydrophobic molecules that can diffuse into the cell
steroid hormones, nitric oxide (NO)
out of the following, list from fastest to slowest diffusion into a cell (without tm channel or receptor): hydrophobic molecules, large uncharged polar molecules, ions, small uncharged polar molecules
hydrophobic molecules, small uncharged polar molecules, large uncharged polar molecules (not super readily by themselves), ions (don’t cross)
ic receptors bind small hydrophobic signaling molecules, what transports them through hydrophilic ec space
carrier proteins
small hydrophobic signaling molecules are released from the carrier and diffuse into target cell, what are they often bound by inside the cell
often bound by nuclear receptor superfamily
t/f all members of nuclear receptor superfamily are in the nucleus
false! they got the name bc everything that they bind eventually end up in the nucleus
describe the structure. of the nuclear super family protein structure (the receptors are specific but structures are common)
- n terminal transcription activating domain activates transcription of target genes
- middle dna-binding domain binds promoters of specific target genes
- c terminal ligand binding domain binds to small hydrophobic signaling molecules
why are orphan nuclear receptors called that
bc they bind to unknown ligand
nuclear receptor superfamily proteins are both the ________ and the _______
receptor and effector
describe how nuclear receptor superfamily proteins act as both the receptor and effector
- ligand binding causes a conformational change in the protein
- dna binding domain (middle section of receptor) is now free to bind promoters of target genes
- inhibitory proteins are released and coactivator proteins are recruited (the cooh on the receptor is like a latch to keep the ligand in)
NO is made from?
arginine
explain the actions of NO
- NO is fast and locally acting due to instability (half life is 5-10 seconds)
- NO can diffuse out of endothelial cells and activate signaling in smooth muscle cells
- acetylcholine activates the receptor on endothelial cells. leads to IP3 and Ca2+ activation to activate NO synthase, arginine is made into NO, there is rapid diffusion of NO across the membrane
- NO binds to guanylyl cyclase in smooth muscle cells to turn GTP to cyclic GMP which leads to rapid relaxation of muslce cells
describe endothelial cells
they are the epithelial cells lining the lumen of BV
state the ligand that activates the receptor on endothelial cells
acetylcholine
state the name of the enzyme that 1. converts arginine into NO
2. that NO binds to to convert gtp to cyclic GMP
- NO synthase
- guanylyl cyclase
where are the following enzymes located
1. NO synthase
2. guanylyl cyclase
- endothelial cells
- smooth muscle cells
state the effect of guanylyl cyclase
rapid relaxation of smooth muscle cells after turning gtp to cyclic gmp
light is not considered a ligand but what can it do
it can initiate signaling events in some cells after affecting a cryptochrome
As part of your CSB498 project, you have replaced the C-terminus of the
nuclear receptor superfamily protein for cortisol with the C-terminus of the
nuclear receptor superfamily protein for vitamin D; what do you expect to
observe in cells that express this chimeric receptor?
a) Cells will activate cortisol responsive genes when exposed to cortisol.
b) Cells will activate cortisol responsive genes when exposed to vitamin D.
c) Cells will activate vitamin D responsive genes when exposed to cortisol.
d) There will be no changes to transcription in response to any signal since
the chimeric nuclear receptor superfamily protein will not bind DNA.
B. B bc of the binding domain and transcription activating domain
A is normal, C is the wrong way
a _________ gradient exists across the plasma membrane
electrochemical
for Na and K ions, which goes more in and which is more out
more K in (higher cytoplasmic [C]) more Na out (higher ec [C])
ion-channel-coupled receptors are _______ by a signaling molecule and are usually closed until a signal is received
gated
describe the events are a ion-channel-coupled receptors are activated
the channels open and mediate passive transport, their ions will flow down their electrochemical gradient
list the 4 ion channels and what is means to be open or closed
- voltage gated: charged AA may move depending on charges of ions of other sides. When closed the ec is + and cytosol is -, when open cytosol is + and ec is -
- ligand gated (ec ligand)
- ligand gated (ic ligand)
- mechanically gated: like a stretch
ion channels are important during ___________ signaling
synaptic
explain how ion channels are important during synaptic signaling, in POV of ion channel
resting synapse:
1. synaptic vesicles of NT are waiting near the PM of the pre-synaptic cell
2. gated ion channels in the target cell are closed
active chemical synapse:
3. a nerve impulse causes NT release by vesicle fusion to the PM
4. NT in the ec space open the ligand gated ion channels in the target cell
5. ions move into the target cell down their [C] gradient, triggering responses in the target cell
what type of ion channel is on the post-synaptic neuron
ec ligand gated ion channel
how many gpcr in humans and what are they activated by
over 800 in humans, activated by small molecules, light, proteins etc
how many tm domains do gpcrs have
7 tm domains
list the subunits of a heterotrimeric large g prot complex
Ga, Gb, Gγ
which g protein subunits have covalently linked lipid tails in the plasma membrane
Ga and Gγ
t/f GPCRs bind diff G proteins
true
what does the activated GPCR act as
GEF to exchange GDP for GTP on Ga subunit
which subunit does GPCR act as a GEF on
Ga subunit
gtp bound Ga is active or inactive
active
what happens when the GPCR gets activated
GTP-Ga dissociates from the Gbγ *depends on the g protein
which subunits of the g protein complex are left together after activation
Gbγ
t/f both Ga and Gbγ CAN activate different targets
true; sometimes a activates, sometimes bγ, sometimes both separately, sometimes both tgt
what is the name of the domain on Ga subunit that interacts with the GPCR during GEF activity
the Ras domain
how do the regulator of G protein signaling act (RGS)
they can act as a GAP to promote GTP hydrolysis by Ga = inactive. overtime the GTPase activity of Ga hydrolyzes GTP to GDP but RGS promotes it
Ga has _________ activity
GTPase
after the hydrolysis of Ga happens, what occurs
this makes Ga inactive and GDP bound Ga will re-associate with Gbγ
will active or inactive Ga re-associate with Gbγ
inactive - GDP bound
different G proteins activate different signaling pathways, state some functions (2)
- some signal through adenylyl cyclase to make cAMP
- some activate phospholipase enzymes to signal through lipids and Ca2+ channels
*these examples are mediated by Ga
what is cAMP
a small molecule secondary messenger
which enzyme synthesizes cAMP and what is the substrate
cAMP is synthesized from ATP by adenylyl cyclase
which enzymes degrades cAMP and what is the product
cAMP is broken down to AMP by cAMP phosphodiesterase
cellular concentrations of cAMP are usually very ______ but large amounts are made in response to _________
low, signals
adenylyl cyclase can be activated by ? subunit and what is the name of the complex
Ga of the Gs complex (heterotrimeric large g protein complex)
explain how Ga can activate adenylyl cyclase
- GPCR activates the heterotrimeric G protein complex Gs
- GTP bound Ga from Gs activates adenylyl cyclase (then it can convert ATP to cAMP)
what can protein kinase A (PKA) be activated by
cAMP
distinguish between inactive and active PKA
inactive PKA: 4 subunits: 2 regulatory subunits and 2 catalytic subunits
Active PKA: 2 molecules of cAMP bind each regulatory subunnts, catalytic subunits are released and are now active kinases
which subunit of PKA bind to cAMP and which turn into kinases when activated
regulatory bind, catalytic = kinases
explain the steps of Gs signaling via cAMP, PKA, and CREB
- Ligand binds and activates the GPCR
- Activated GPCR acts as a GEF to exchange
GDP for GTP on the G⍺ subunit of Gs - GTP-G⍺ activates adenylyl cyclase
- Adenylyl cyclase coverts ATP to cAMP
- cAMP binds regulatory subunits of PKA to
release the catalytic domains from inhibition - Activated PKA moves to the nucleus
- Activated PKA phosphorylates CREB
- CREB-binding protein + phosphorylated
CREB bind cAMP-responsive element (CRE)
to activate transcription of target genes
GPCRs and cAMP mediate sense of _____ for humans
smell
how many GPCRs do humans have to recognize different odarants
~350
each olfactory neuron expresses _____ copies of _____ GPCR type per neuron in the cilia
many, one
explain how GPCRs signal through Golf and cAMP
- odorant recognition (ligand) activates the GPCR which acts as a GEF on Ga of Golf of that neuron
- Golf triggers cAMP production by adenylyl cycles, converts ATP to cAMP
- cAMP opens cAMP gated cation channels
- cation influx triggers an action potential (= sense of smell)
explain why we can or cannot smell pizza, carbon monoxide, and why dogs can smell for cancer
pizza: smell is a compilation of diff odorants
CO: we don’t have the GPCR that binds to CO
cancer: specific chemicals released that dogs can smell
explain how some G proteins can signal by triggering phopholipase C-β
- GPCR activates the heterotrimeric G-protein complex Gq
- GTP bound Ga from Gq activates phopholipase C-β
explain how some G proteins can signal by triggering diacyclglyerol and IP3 production
- Phospholipase C-β (PLCβ)
cleaves PI(4,5)P2 to
produce diacylglycerol
(DAG) & IP3 - DAG diffuses in the
membrane to activate
protein kinase C (PKC) - IP3 diffuses in the
cytoplasm to open Ca2+
channels in the ER - Both DAG & IP3 are small
molecule secondary
messengers
what are DAG and IP3
small
molecule secondary
messengers
which enzyme cleaves PI(4,5)P2 to
produce diacylglycerol
(DAG) & IP3
phospholipase C-β
describe Gq signaling via DAG, IP3, Ca2+, and PKC
- Signal activates GPCR
- GPCR makes GTP-G⍺
on Gq, releasing Gβ𝛾 - GTP-G⍺
activate PLCβ - PLC cleaves PI(4,5)P2
to DAG & IP3 - IP3 opens a gated Ca2+ channel
in the ER - Ca2+ moves into the cytoplasm
- DAG & Ca2+ activate PKC (coincidence detector)
- PKC phosphorylates downstream targets
in the Gq signaling pathway, what acts as a coincidence detector and what does it detect
PKC, detects DAG & Ca2+
Gq activates ? (enzyme) on which of its subunits
Gs activates ? (enzyme) on which of its subunit
Gq = phospholipase C-β on Ga
Gs = adenylyl cyclase on Ga
You have discovered that a particular virus completely destroys the human
sense of smell during infection. How might this occur?
a) The virus causes production of a protein that inhibits a specific GPCR.
b) The virus causes production of a protein that inhibits Gq.
c) The virus causes production of a protein that inhibits CREB
phosphorylation.
d) The virus causes production of a protein that inhibits adenylyl cyclase.
D.
A is wrong bc we still have ~394 GPCRs, you can’t smell ONE thing. B is wrong bc Golf would work. C is wrong bc it’s the cAMP in step 4 for smell, not CREBS (step 8)
