Chapter 15 Flashcards
2 methods of signal transduction
1) activation of receptors can transmit a signal ( g protein) to activate an enzyme (effector) that creates second messengers
2) activation of a receptor can cause it to change into a recruiting and docking station for other signalling proteins.
in most signaling pathways, proteins are activated by
phosphorylation/dephosphorylation
draw the mrna syntheiss signal transduction pathway
involves three PKs and a transcription factor
Activation of Receptor protein Tyr Kinases often results in ____ followed by activation of a protein kinase domain
dimerization
GPCRs interact with ____ proteins to activate an effect
G proteins
how is the inactive version of a GPCR stabilized? what happens when a ligand bind to the GPCR?
inactive conformation is stabilized by noncovalent interactions between AAs in the 7 helices. ligand disturbs the non covalent interactions, changing the conformation to Active State.
In what state does G protein bind to GPCR
GDP-Gprotein state
where does GDP/GTP bind to on the G protein
on G alpha subunit, causes dissociation and it binds to the effector to activate it, making the effector create second messengers
GPCRS bind specifically to ____ G proteins
heterotrimeric
when will G alpha subunit remove itself from the effector that it is activating?
when GTP hydrolysis occurs, amknig the Glpha back into GDP-Galpha. It will return back to the heterotrimeric form of G protein.
2 steps to GPCR de-sensitization
1) GRKs phosphorylate the G protein RECEPTOR, tagging it with a phosphate
2) arrestin proteins bind with the phosphorylated G protein receptor and compete with the actual G proteins for a spot on the GPCR.
Arrestin can also bind with AP2 adaptor proteins that are situated on RME clathrin coated pits, promoting the uptake of GPCR via endocytosis.
How does arrestin cause the GPCR to be absorbed into the cell?
In addition to acting as a competitive inhibitor at the binding site of the G protein on the GPCR,
Arrestin can also bind with AP2 adaptor proteins that are situated on RME clathrin coated pits, promoting the uptake of GPCR via endocytosis and end up in the endosome
How do Regulators of G protein signalling (RGSs) help with de-sensitization?
they help terminate the response of the effector by speeding up GTP hydrolysis of the G alpha subunit, deactivating the effector.
how does cholera target G proteins?
they inhibit the G alpha ATPase activity, and thus Atp is never hydrolyzed- the effector is always on and the intestinal tract will continue to secrete muscus, resulting in dehydrateion
2 main types of second messengers we studied
1) caMP
2) phosphatidyl inositol 2nd messengers
how are phoshatidyl inositol groups converted into second messengers
when ACh binds onto a GPCR resulting in G protein activation, the G alpha subunit activates a PHOSPHOLIPASE (PILC BETA), which can cleave a phosphatidyl insotiol phosphate molecule into DAG and IP3. DAG and IP3 are second messengers that trigger change in the cell
PI is phosphorylated by ___, creating PIP(4). PIP is phosphorylated by ____, creating PIP2(4,5). PIP2 is phosphorylated by ____,creating PIP3 (3,4,5).
PI is phosphorylated by PI4K, creating PIP(4). PIP is phosphorylated by PI5K, creating PIP2(4,5). PIP2 is phosphorylated by PI3K,creating PIP3 (3,4,5).
where are the phosphotidyl inositoll groups located when they are being phoshphorylated?
located in the membrane.
Which phosphatidyl inositol derivative is located broken down into DAG and IP3? Which PI derivative is responsible for the insulin response?
PIP2, PIP3.
PILC, and effector that gets activated by a G protein, cleaves PIP2 into ___ and ____
DAG and IP3
What does IP3 do?
binds to an IP3 receptor in the smooth ER which triggers to outflux of Ca2+ ions into the cytosol, which can trigger different events in a cell (muscle contraction, exo and endocytosis, etc)
What does DAG do?
remains in the plasma membrane and activates the PKC effect, to phosphorylate other target proteins
glucagon and epinephrine bind onto _____ receptors
Different types of GPCRs (ex/ beta adrenergic receptors)
the binding of glucagon or epinephrine onto a GPCR triggers the activation of a ____ (effector), which produces cAMP.
the G protein activates adenylyl cyclase, which produces cAMP from ATP.
glycogen synthase converts ____ into ____
glycogen phosphorylase converts ____ into ____
glycogen synthase converts UDP-Glucose into Glycogen
glycogen phosphorylase converts Glycogen into GLucose-1-Phosphate
glucagon is produced in the ____ cells of the ____, whereas insulin is produced in the ____ of the ____
glucagon is produced in the ALPHA cells of the PANCREAS, whereas insulin is produced in the BETA of the PANCREAS
anabolic enzymes are ____ when phosphorylated. Catabolic enzymes are ____ when phoshphorylated
anabolic enzymes are DEACTIVATED when phosphorylated. (EX/ GLYCOGEN SYNTHASE
Catabolic enzymes are ACTIVATED when phoshphorylated (PHOSPHORYLASE KINASE, GLYCOGEN PHOSPHORYLASE)
CAMP is broken down into AMP via
phosphodiesterase
Draw the pathway from glucose metabolism in response to glucagon
1) glucagon binds to GPCR, which recruits GDP-Gprotein. 2) GDP-G protein gets converted to GTP-G protein, and the alpha subunit dissociates and binds to adenylyl cyclase effect
3) adenylyl cyclase catalyzes ATP to cAMP
4) cAMP activates PKA
5) PKA can do three things:
- move to nucleus and phosphorylate CREB TF, which gets activated to create proteins involved with gluconeogenesis
- phosphorylate glycogen synthase, which de activates it and thus there is no more glycogen synthesis
- phosphorylate phosphorylase kinase, which will activae it. phosphorylase kinase will phosphorylate glycogen phosphorylase, activating it, thus triggering glycogen breakdown.
3 things that activated PKA can d0
- move to nucleus and phosphorylate CREB TF, which gets activated to create proteins involved with gluconeogenesis
- phosphorylate glycogen synthase, which de activates it and thus there is no more glycogen synthesis
- phosphorylate phosphorylase kinase, which will activae it. phosphorylase kinase will phosphorylate glycogen phosphorylase, activating it, thus triggering glycogen breakdown.
3 things that activated PKA can do
- move to nucleus and phosphorylate CREB TF, which gets activated to create proteins involved with gluconeogenesis
- phosphorylate glycogen synthase, which de activates it and thus there is no more glycogen synthesis
- phosphorylate phosphorylase kinase, which will activae it. phosphorylase kinase will phosphorylate glycogen phosphorylase, activating it, thus triggering glycogen breakdown.
what enzyme would be needed in order to increase glycogen synthesis
glycogen phosphatase would DE PHOSPHORYLATE glycogen synthase, activating it, thus allowing for glycogen synthesis.
in the liver, cAMP triggers ____
in the fat cells, cAMP triggers ____
in the smooth muscle cells, cAMP _____
in the liver, cAMP triggers GLYCOGEN BREAKDOWN and INCREASED GLUCONEOGENESIS
in the fat cells, cAMP triggers TAG BREAKDOWN
in the smooth muscle cells, cAMP Decreased relaxation
How are PKAs held down to specific regions of the cell?
using PKA anchoring proteins called AKAPs. AKAPs concentrate PKA to a certain region and concentrates its substrates to the same region so that
rhodopsin is an example of a
GPCR, and is responsible for black and white vision because it interacts with transducin g protein
when a GPCR is too active, it is considered a _____
gain of function mutation
when a GPCR is too insensitive to a ligand and cannot recruit G proteins when activated, it is considered a ____-
loss of function mutation
enzymes that phosphorylate tyrosine resides on target proteins
protein tyrosine kinases
example of a protein tyrosine kinase
receptor tyrosine kinases
ligand mediated dimerization versus receptor mediated dimerization
ligand mediated: a BIVALENT ligand attaches to 2 RTKs at the same time, causing the two receptors to dimerize. Dimerization exposes the kinase sites of the two receptors and they trans autophosphorylate each other.
receptor mediated: binding of one monovalent ligand to each of the 2 RTK’s triggers dimerization. Dimerization exposes their kinase site and they trans auto-phosphorylate each other.
the RTK dimers are now phosphorylated and active. they can act as recruiting stations for proteins to bind onto or they can phosphorylate other molecules
which type of domain is required in order for a protein to be able to bind onto a tyrosine kinase?
SH2 or PTB domain
RTKS contain ________ which allows a dimer to phosphorylate itself via trans autophosphorylation
intrinsic Tyr kinase activity
GRB2 contains a ____ domain and interacts with ____kinase . GRBs functions as an _____ protein for _____
GRB2 contains a SH2 domain and interacts with RTK . GRBs functions as an ADAPTOR protein for SOS
What is SOS?
SOS is a guanine nucleotide exchange factor (GEF) for RAS, an enzyme involved in the MAP protein cascade for transcription factors.
IRS (insulin receptor substrate) contains a ____ domain and interacts with ______ receptors, a type of RTK. IRS functions as both an adaptor protein and a ______station for other proteins, such as _____
IRS (insulin receptor substrate) contains a PTB domain and interacts with IR receptors, a type of RTK. IRS functions as both an adaptor protein and a DOCKING station for other proteins, such as SHP2, Grb2, P13K.
What is SHP2?
a protein that is capable of binding to IRS, which is bound to an RTK. Binding of SH2 activates it into a protein tyrosine phosphatase.
T/F: PIPLC, P13K and Shp2 can bind directly to RTK without binding to IRS or anything
True. Also, Grb2 can bind to IRS, which binds to an RTK (IR), or directly to an RTK itself.
STAT is a ____ with a ____ domain that allows it to interact with RTKs. How does RTK activate STAT?
STAT is a TRANSCRIPTION FACTOR with a SH2 domain that allows it to interact with RTKs.
After RTK phosphorylates itself in dimer form (gets activated), it can phosphorylate a tyr residue on STAT molecules, resulting in phosphorylated STAT molecules dimerizing together and entering the nucleus to act as a transcription factor.
RTK activation can also lead to the breakdown of PIP2 into DAG and IP3. How?
activated RTK can bind PILC GAMMA phospholipase, activating it. Phospholipase gamma can then break apart PIP2, just like how phospholipase beta can (PILC B is activated by a G protein)
What is ras and how is it connected to an RTK?
Ras is a G protein that is embedded into the membrane. Its activation is involved with setting the stage for the Map kinase pathways.
It is connected to an RTK by GRb2. when RTK is activated, Grb2, which contains an SH2 domain, is recruited and binds to RTK. Grb 2 acts as an adaptor protein which binds SOS, SOS is a GEF for Ras, and SOS can activate Ras.
the _____ cycle uses _____ proteins to mediate Ras activity.
the G protein cycle uses accessory proteins to mediate Ras activity.
3 main accessory proteins used in the G cycle to maintain G proteins such as Ras
1) GDI: guanine nucleotide dissociation inhibitor. Prevents GDP from being exchanged to GTP. makes protein remain in inactive form
2) GAP: GTPase activating protein: speeds up the rate of GTP hydrolysis on a G protein.
3) GEF: guanine nucleotide exchange factor. helps dissociate GDP in exchange to GTP, activating the enzyme.
if GDI binds to a G protein, would it get activated?
no. GDI prevents activation by inhibiting the exchange o GDP to GTP
Ras MAP kinase pathway activates ______ that are involved in ___
transcription factors involved in cell proliferation and differentiation
How does the Ras Map kinase pathway get activated?
by a growth factor like EGF when it binds to an RTK
How does an RTK get activated to initiate the MAP kinase pathway?
when a growth factor binds to the RTK, triggering dimerization and transautophosphorylation
Steps of the RAS MAP kinase pathway
1) growth factor binds to RTK and it undergoes dimerization and transautophoshphorylation to activate
2) activated RTK recruits adaptor protein Grb2 to attach SOS and Ras to the RTK
3) SOS is activated and acts as a GEF, activating ras by giving it GTP
3) GTP-ras activates Raf (MAPKKK), bringing it to the membrane and phosphorylates it, making it activated membrane-bound raf
4) membrane raf activates MEK, a MAPKK, activating it via phosphorylation
5) P-MEK activates ERK into P-ERK, (MAPK), activating it
6) MAPK/P-ERK phosphorylates a transcription factor, which activates and enters the nuclues, causing the production of proteins in volved in cell splitting, cell proliferation (D1 protein production) as well as MPK-1 to turn off the MAPkinase pathway
MAPKKK aka ____
MAPKK aka ____
MAPK aka____
MAPKKK aka Raf
MAPKK aka Mek
MAPK aka ERK
how is the map kinase pathway turned off?
the transcription factors triggers the production of an MKP1 protein, which de phosphorylates MAPK/ERK, de activating the map kinase pathway
An insulin receptor is an _____
RTK
Insulin receptors bind ____
IRS (insulin receptor substrates)
structure of IR. which chain does insulin bind to? which chain does IRS bind to?
1) alpha chain. where insulin binds on the extracellular space
2) beta chain. where IRS binds on the cytosolic space
alpha and beta chains are held together by disulfide bonds
T/F: Insulin receptors dimerize like other RTKs
false. they are already held together by disulfide bonds. However, they do trans autophosphorylate themselves like other RTKs
T/F: Insulin receptors dimerize like other RTKs
false. they are already held together by disulfide bonds. However, they do trans autophosphorylate themselves like other RTKs
IRS’s bind to IRs by their ____ domain. When bound, they act as both ___ and ___ proteins. What types of proteins can IRS’s bind to once they are on the IR?
IRS’s bind to IRs by their PTB domain. When bound, they act as both adaptor and docker proteins. When bound, shp2, PI3K, and Grb2. the most notable is the P13K protein, which helps induce glucose uptake.
How does P13K get activated and what does it do?
When an IR gets activated, IRS binds to it via its PTB domain and gets phosphorylated at its tyrosine sites. IRS acts as a docking station and P13K can bind to it, getting activated. when P13K gets activated, it catalyzes the reaction from PIP2 to PIP3, and also activates PDK1.
PDK 1 and another enzyme called Mtorc2 can phosphorylate PKB at its T308 and S473 residues, activating PKB. once PKB/AKT gets activated, it can regulate GLUCOSE transport from the blood into the cells by making glut 4 receptos fuse to the plasma membrane.
PKB drives glucose back into the cells from the blood stream in response to insulin. What protein kinase is inhibited by the presence of PKB?
PKA or GSK-3. With no PKA activity, glycogen synthase can get activated.
What two proteins are needed to activate PKB? where do they phosphorylate
PDK 1 phosphorylates T308
MTORC 2 phosphorylates S473
phosphorylation activates PKB.
4 main processes of activated AKT/PKB
1) drives GLUT4 to fuse to the plasma membrane
2) inhibits PKA and activates glycogen synthase
3) Apoptosis
4) Cell proliferation
Diabetes is caused by defects in ____ signalling. Type 2 is the body cannot bring glucose out of the blood stream due to ______
Diabetes is caused by defects in INSULIN signalling. Type 2 is the body cannot bring glucose out of the blood stream due to INSULIN INSENSITIVITY
plants DO NOT have RTKS. What’re their versions of RTKs?
they can phosphorylate their HISTIDINE RESIDUES instead of TYROSINE residues, triggering simliar pathway to MAPkinase pathways
in resting state, calcium concentration in cytosol is __
low
ways calcium channels can be opened
1) by an action potential
2) by Na+ channels opening and causing cell depolarization, opening voltage gated Ca2+ channels
3) by the presence calcium (rynodine receptors)
____ can get cleaved by PILC B or PILC G, forming DAG and IP3. Ip3 can trigger _____ release from the SR to the cytosol
PIP2 can get cleaved by PILC B or PILC G, forming DAG and IP3. Ip3 can trigger Ca2+ release from the SR to the cytosol
How does the normal concentrations of the cytosol stay low?
Na+/Ca2+ channels pumps Ca2+ out for every 3 Na+ inside the cell.
_____ receptors in the SER is involved in the phenomenon of calcium induced calcium release
Rynodine receptors. they open in response to Ca2+ in the cytosol, releasing even more Ca2+ to flow from the SEr into the cytosol
the influx of cytosolic Ca2+ allows Ca2+ to bind to troponin, which binds to tropomyosin, exposing the myosin binding sites on actin, allowing for muscle contraction.
3 receptors that will increase cytosolic ca2+ concentration
1) voltage gated Ca2+ channels
2) IP3 receptors
3) Rynodine receptors
____ is a dye that would allow for Ca2+ visualization
Flura-2
purpose of having calcium in the cytosol
1) neurotransmitter transmission (allows transmitter vesicels to fuse)
2) fertilization
3) muscle contraction
SOCE
store operated calcium entry
What happens during SOCE
Ca2+ levels in the smooth ER are deteced and triggesr a response to the opening of Ca2+ channels in the plasma membrane, allowing Ca2+ to enter the cytosol, where a pump can pump cytosolic ca2+ into the SER to replete its stores
Mechanism of SOCe
1) ER depletion of calcium triggers STIM1 proteins to move onto SER membrane regions that are near the plasma membrane
2) STIM 1 on the SER recruits ORAI I on the plasma membrane, triggering calcium channels to open
3) Contact between STIM1 and ORAI 1 open the calcium cahnnels and calcium ions flow into the cell to be pumped into the SER
Convergence
when signals from unrelated receptors trigger the same sort of response
examples of convergence
1) ACh Binding to a GPCR, triggering G proteins to activate PILC-B effector causes PIP2 to breakdown into DAG and IP3
Activated RTK can recruit PILC GAMMA, activating the phospholipase and triggering PIP2 to breakdown into DAG and IP3
2) GPCR, Integrins and RTKs can all get activated by their respective ligands, and Grb2 can bind to any of these activated receptors to activate the Map Kinase Cascade by attaching SOS to Ras
Examples of Divergence.
1) Insulin receptor substrate can bind to an IR, which is a type of RTK, but, it can trigger different pathways afterwards:
- IRS can dock Grb2, which triggers the MAP kinase cascade
- IRS can dock PI3K, which triggers glucose uptake
2) RTK can activate three difference pathways:
- can activate PLC-G, causing PIP2 –> IP3 and DAG
- IRS can bind to RTK, allowing Grb2 to bind and signal the map kinase casade
- IRS can bind to RTK (IR) and PI3K can bind to IRS, causing glucose uptake
- STAT could bind to RTK and cause transcription factors to promote protein synthesis
examples of cross talk
cAMP can block signals transmitted through MAP kinase cascade. PKA inhibits Raf of the MAPKinase, preventing Map kinase from activating transcription factors like CREB
BUT
cAMP can activate the transcription factor CREB without the MAP kinase pathway by activating PKA, which can phosphorylate KREB direcly while inhibiting MAPKKK
how does Ca2+ and cAMP influence each others pathways? Which kind of pathway interaction is this considered to be?
Ca2+ can bind to calmodium calcium receptor to activate it, similar to how cAMP can bind to PKA to activate it. this both results in activation of CREB. this is considered Convergence because two different receptors can trigger the same response.
Ca2+ increase from IP3 can inhibit PKC activity that was induced by DAG, which is considered cross talk.
NO is produced by ___ synthase, using ___ (AA) and O2 as starting material.
NO is produced by nitric oxide synthase, using ARGININE (AA) and O2 as starting material.
NO stimulates ____, making ____ (secondary messenger)
NO stimulates Guanylyl cyclase, making cGMP (secondary messenger)
how is NOS activated to crease NO?
activated by increased calcium ions in the cytosol when ACh binds, triggering the opening of voltage dependent Na+ ions, which flow in and open calcium ion channels.
when cGMP is produced in response to NO, it activates ____, which causes smooth muscle and blood vessel dilation
when cGMP is produced in response to NO, it activates PKG, which causes smooth muscle and blood vessel dilation
How does NO help with angina?
giving NO pushes out cytosolic Ca2+. relaxing smooth muscle in the heart whos constriction is resulting in angina
How does NO help with penile erection? What does viagra do?
NO is created by the penile glands to relax blood vessels and increase blood flow by creating cGMP. cGMP created by NO activating guanylyl cyclase. Viagra deactivates guanylyl phosphodiesterase and prevents the breakdown of cGMP, which allows the blood vessels to stay open longer.
How does nitric oxide aid as a messenger?
1) Ach binds to receptor, causing Na+ to increase in the cell, triggering Ca2+ channels to open
2) rise in Ca2+ concentration
3) ca2+ activates Nitric oxide synthase
4) NO activates guanylyl cyclase
5) cGMP is produced and binds to PKG
6) PKG causes muscle relaxation
4 characteristics of a cell that died via apoptosis
1) blebs
2) volume loss
3) fragmented DNA
4) loss of adhesion to other cells
Caspase. it is manufactured in its ______ form
a serine protease that carries out cell death. made by the cell in its zymogen/procaspase form
4 main target proteins by caspases
1) focal adhesion kinases (FAK) to disrupt cell adhesion
2) lamin breakdown to begin to fragment the DNA
3) cytoskeleton proteins; IFs, Actin, MTs
4) Caspase activated DNAses: Caspase ACTIVATE enzymes that breakdown DNA
Mechanism for Extrinsic Pathway of Apoptosis
1) external stress is inflicted on the cell (radiation)
2) external stress triggers TNF to bind to TNF receptor
3) TNF receptor contains a death domain that recruits FADD AND TRADD adaptor proteins
4) FADD AND TRAD bind to procaspase 8
5) procaspase 8 activates initiator caspase 8
6) initiator caspase 8 activates the executioner caspases, leading to cell death.
TNF
tumor necrosis factor
TNF1 Receptors are located on the _____ and have specific ____ domains that are involved in apoptosis.
located on plasma membranes and contains a death domain
release of mitochondrial protein _____ can intrinsically trigger apoptosis
cytochrome C
activation of the intrinsic pathway is regulted by _____ family of proteins, which contain BH domains
Bcl-2
3 Main types of Bcl proteins
1) proapoptotic members (Bax and Bak)
2) anti-apoptotic members
3) BH3 members only- promotes Apoptosis (bad, bid, bin, puma)
mechanism for internal apoptosis
1) internal event (ex/ too much calcium in cytosol) activates Bak or Bax on the mitochondria, a group of proapoptotic proteins.
2) Bak or Bax binds to the OMM of the mito and forms leaky mito channels
3) cyt c leaks out from the Bak induced channels and associates with APAF-1 and PROCASPASE-9 to form an APOPTOSOME
4) in the apoptosome, procaspase 9 gets activated to casase 9, which can activate down stream executioner caspases
during the intrinsic pathway of apoptosis, cyt c leaks out from the Bak induced channels and associates with ____and ____ to form an _____, which can activate caspase 9
cyt c leaks out from the Bak induced channels and associates with APAF-1 and PROCASPASE-9 to form an APOPTOSOME
How does the body get rid of dead cells?
macrophased eat the dead cell via phagocytosis
-alive cells have phosphatidyl serine on the inside of the plasma membrane, but during apoptosis, scramblases place phosphatidyl serine on the outside, signalling the macrophages to eat the dead cell.
T/F: during apoptosis, cytosol and organelles of the cell can flow out of the leaky plasma membrane into the extracellular space
false. cytosolic content is held within the plasma membrane of the apoptotic cell. nothing spills out. killed from the inside.
