Exam 2: Topic 6 Flashcards
what are the 3 classes of signaling molecules? (not types of neurotransmitters)
- cell impermeable
- cell permeable
- cell associated molecules
cell impermeable molecules
Signal NT can be contained in a lipid vesicle
- Receptors must be on the cell surface on the postsynaptic cell
- Most NTs ⇒ ligand gated or GPCRs
cell permeant molecules
Signal can pass through lipid bilayer and can not be contained in a lipid vesicle
- Receptors are intracellular or in the nucleus of the cell
- These can bind to receptors when they are in the membrane of the cell
examples of cell permeant molecules
Endocannabinoids, NO, estrogen (hormones)
cell associated molecules
Cell adhesion molecules ⇒ integrins, cadherins, eph/ephrin
- Binds to a receptor on the postsynaptic cell
- Keeps the cells attached to one another
T/F cell associated molecules signal monodirectionally?
False
Can signal bi-directionally
- designation is not straightforward for which is presynaptic or postsynaptic
3 types of chemical signals
- synaptic
- paracrine
- endocrine
synaptic chemical signals
Cells are very close to one another from presynaptic axon terminal and postsynaptic density region
- Ligand can be cell permeant, cell impermeant, or cell associated (most NTs)
- Things can diffuse from the first cell through to the second cell on surface receptors or receptors internally
paracrine chemical signals
Cells are nearby one another but don’t share an active zone/PSD
- Released in the extracellular area and binds to any receptor with a receiving membrane in the neurons around it
what is essential for paracrine signaling?
Ligand can be cell permeant or cell impermeant, but MUST be secreted
types of paracrine signal molecules?
Neuropeptides, endocannabinoids, some hormones
endocrine chemical signaling
Cells are far away from one another ⇒ long distance signaling
- Signals travel through the bloodstream ⇒ has an effect on a tissue or neurons far away from the presynaptic site
- Ligand can be cell permeant or cell impermeant, but must be secreted
types of endocrine signaling molecules
hormones
what are the 3 main types of effector pathways?
- Increase protein phosphorylation
- Increase protein phosphorylation and activate calcium binding proteins
- Decrease protein phosphorylation
what is the general pathway for a signal? (6)
- signal binds to receptor (first messenger)
- activates GPCR
- activates effector
- generates a second messenger (cAMP, etc.)
- turns on or off protein kinases/phosphatases that have a target
- affect a target protein by phosphorylating or dephosphorylating the final protein (like a channel)
signal amplification
activation of a few receptors can cause a late change
- receptor activates multiple G proteins ⇒ these each activate 1 effector protein each
what steps amplify the signaling process and which are neutral?
- receptor to G protein (amplification)
- G protein activates an adenylyl cyclase
- adenylyl cyclase makes cAMP (amplification)
- each cAMP activates protein kinases
- protein kinases transfer phosphates to target proteins (amplification)
what are the two classes of GTP binding proteins (G proteins)?
- heterotrimeric G proteins
- monomeric G proteins
heterotrimeric G proteins (trimeric)
3 proteins bind to the GPCR
- alpha, beta, gamma
monomeric G proteins
Don’t actually bind to G protein coupled receptor but are activated through an intermediary called a GEF
T/F both types of G proteins are only active when bound to GTP?
True
what does hydrolysis of GTP to GDP do?
turns off signaling ⇒ when GTP is bound to trimeric structure its activated but if this is removed and replaced with GDP then it becomes deactivated
what are properties of each component of a trimeric G protein?
- Alpha subunit is a weak GTPase ⇒ enzyme that will take GTP and attach it where GDP was
- binds GTP ⇒ conformational change ⇒ interacts with the effector
- Hydrolyze GTP ⇒ conformational change ⇒ can’t bind effector - Beta and Gamma subunits are less well understood
what have monomeric G proteins been studied in?
cell growth, motility, and cancer
Ras
identified in a virus that causes rat sarcoma tumors
RhoGTPase
regulate cytoskeletal dynamics
GAP proteins
GTPase activating protein
- Activates (strong) the GTPase activity of the alpha subunit of the trimeric G protein or the monomeric G protein
- Prevents the alpha subunit from interacting with the effector ⇒ when activated it finds GTP which allows binding to the effector protein
- reduces/shortens effect of ligand binding to GPCR
does GAP turn the signaling pathway on or off? What about GEF?
GAP turns off the signaling pathway => Can turn off signaling even when ligand is still bound to the GPCR
- GEF turns on the signaling pathway
GEF
GTP exchange factor ⇒ takes GTP and binds it to the ras protein to activate it
- Activates the monomeric G protein (ras)
- Exchanges GDP for GTP
increases/prolongs effect of ligand binding to GPCR
- Can turn on signaling in the absence of ligand
How many transmembrane domains do GPCRs have?
7 domains, 1 subunits
- Can also function as a hetero or homo dimer
which side of a GPCR is associated with the G protein?
the cytoplasmic side
- Receptor binds to trimeric G protein
- Trimeric G protein gets activated
what is the typical signaling pathway for a heterotrimeric G protein? (5)
- chemical signal binds to the extracellular side of the receptor
- GDP on the alpha subunit (beta and gamma are also there) activates and obtains GTP
- alpha unit binds to the effector protein
- GAP takes off a Pi from the alpha subunit so it only has GDP on it again
- this and the beta-gamma subunit all go back on to the GPCR
what is the typical signaling pathway for a monomeric G protein? (3)
- the chemical signal binds to the GPCR on the extracellular side
- an adaptor protein and GEF on the intracellular side activate Ras (which has a GDP on it) by exchanging the GDP for GTP
- Ras is active until GAP takes off a Pi and then Ras becomes inactive again
what types of effector molecules does the alpha subunit interact with from the G protein? (3)
- Adenylyl cyclase (AC)
- Guanylyl cyclase (GC)
- Phospholipase C (PLC)
how many trimeric G proteins does each GPCR bind?
only 1
- Each type of trimeric G protein triggers a different type of signaling
T/F a ligand may have more than 1 type of GPCR?
True
what are trimeric G proteins named for?
their alpha subunits
- alpha s
- alpha i
- alpha q
what is the alpha s G protein subunit pathway?
it activates adenylyl cyclase to convert ATP ⇒ cAMP (2nd messenger) to activate protein kinase A
what is the alpha i G protein subunit pathway?
inhibits adenylyl cyclase => no ATP is turned to cAMP => no Protein kinase A is activated
what is the alpha q G protein subunit pathway?
activates phospholipase C => converts PIP2 into either DAG or IP3
1. DAG activates protein kinase C
2. IP3 => activates calcium => activates protein kinase C or CaMK (calcium does a lot of activating)
neurons with dopaminer receptors typically express which types of receptors?
mostly D1 or mostly D2, but may express low amount of the other receptors
how do dopamine receptors form the Gq?
When D1-D2 act as a heterodimer, they signal to Gq
what type of pathway does D1R initiate?
the alpha s pathway activating kinase A
what inhibits cAMP and therefore protein kinase A activity?
cAMP phosphodiesterase
what pathway does D2R activate?
the alpha i pathway to inhibit protein kinase A
what pathway do D1-D2R complexes activate?
the alpha q pathway initiating Kinase C activity and also CaMK activity as a secondary product (calcium binding proteins)
what happens with too much cyclase AMP and protein kinase?
a dysfunctional nervous system
what pathway does norepinephrine activate?
the Gs pathway increasing kinase A
- called a beta-adrenergic GPCR
what pathway does glutamate activate?
Gq pathay
- called a mGluR GPCR
what pathway does dopamine activate?
Gi pathway deceasing kinase A
- called a D2 GPCR
what are types of second messenger molecules?
- Ca2+
- cAMP
- cGMP
- IP3
- Diacylglycerol
what are sources of calcium? (2 main w/ subcomponents)
- plasma membrane (extracellular)
- VG Ca2+ channels
- Ligand gated Ca2+ channels - ER membrane (intracellular)
- IP3 gated Ca2+ Channel
- Ryanodine gated Ca2+ channel
how is calcium removed? (3)
- Na+/Ca2+ exchanger in the plasma membrane
- Ca2+ pumps
- Plasma membrane
- ER
- Mitochondria - Calcium binding proteins (calbindin)
IP3 receptor has what kind of pathway?
Gq type pathway because IP3 is a second messenger that will activate the channel to let ER calcium come into the cytoplasm
Ca2+ targets (6)
- CaM (Calmodulin)
- protein kinases
- protein phosphatases
- ion channels
- synaptotagmins
- other Ca2+ binding proteins
what are sources of cAMP?
adenylyl cyclase converts ATP to cAMP
intracellular targets of cAMP
- protein kinase A
- cyclic nucleotide gated channels
removal of cAMP
cAMP phosphodiesterase
- cAMP back to AMP
sources of cGMP
guanylyl cyclase converting GTP to cGMP
intracellular targets of cGMP
- protein kinase G
- cyclic nucleotide gated channels
removal mechanisms of cGMP
cGMP phosphodiesterase
- converts cGMP to GMP
IPs sources
phospholipase C acts on PIP2 to make IP3
intracellular targets for IP3?
IP3 receptors on ER
removal mechanisms of IP3
phosphatases
sources of DAG
phospholipase C on PIP2
intracellular targets of DAG
protein kinase C
removal mechanisms of DAG
various enzymes
what are AMPA and NMDA involved in?
long term depression and long term potentiation
what do IP3 receptors do?
release Ca2+ into the cytoplasm
what are the structure and function of target proteins altered by? (2)
- Protein kinases (phosphorylating proteins)
- Protein phosphatases (dephosphorylating proteins)
what type of protein is kinase A (PKA)?
a heterotetramer
- 2 regulatory units
- 2 catalytic units
what happens to the structure of PKA when camp molecules bind?
the regulatory subunits the conformation of the protein will change and the catalytic subunits are released
- The catalytic subunit will go and phosphorylate substrates Ser or Thr residues on proteins
how many cAMP molecules must bind to PKA?
4
how is CaMKII activated?
by a rise in the intracellular concentration of Ca2+ through calmodulin
- Calcium binds to calmodulin and when bound it becomes activated (CaM)
- When CaM is activates it takes CaMKII and binds to it which causes a conformational change ⇒
what happens to the subunits when CaMKII is activated?
the regulatory and catalytic subunits extend outward from the middle linker (green)
- there is a string between the main domain and the upper and lower catalytic subunits that extend off of it
- The catalytic subunits phosphorylate Ser and Thr
how is PKC activated? What happens?
by Ca2+ and DAG
- the regulatory and catalytic domains will separate when activated to phosphorylate Ser and Thr residues
- the catalytic subunits are connected to the regulatory unit which have a lipid binding domain attached to it
how is calcineurin (PP2B) activated?
by Ca2+ and Calmodulin (CaM)
- like CaMKII
what does PP2B do?
Instead of phosphorylating a target protein it dephosphorylates the target protein
- This keeps the phosphorylation in check
what proteins increase current conductance through NMDA and AMPA receptors? (3)
- PKC
- PKA
- CaMKII
what protein deceases current conductance through NMDA and AMPA receptors?
Calcineurin (PP2B)
what protein decreases conductance through VG K+ channels?
PKA => probably alpha i G protein subunit
what protein increases conductance through VG Ca2+ channels?
PKA => probably alpha S G protein
CREB
in the nucleus and is a cAMP response element binding protein => activates transcription of CRE/CaRE
CRE
a sequence in the gene protein that regulates transcription
pCREB
protein kinase active form that is found in the nucleus and binds DNA ⇒ phosphorylates CREB
what is the G protein coupled pathway to activate CREB and then CRE? (7)
- GPCR and ligand bind
- G protein comes off and activates adenylyl cyclase
- Adenylyl cyclase produces cAMP from ATP
- cAMP activates protein kinase A
- Protein kinase A catalytic domains migrate to the nucleus and bind/activate CREB
- CREB translates transcription of DNA
- The mRNA resulting can make new proteins
what is the Ca2+ channel pathway to activate CREB and then CRE? (4)
- CamKIV can be activated by calcium coming in from the extracellular space
- This will then activate CREB
- CREB translates transcription of DNA
- The mRNA resulting can make new proteins
end card
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