Molecular Signaling in Neurons Flashcards
3 classes of cell signaling molecules
Cell impermeant molecules
Cell permeant molecules
Cell associated molecules
Most neurotransmitters are ___ ____ molecules.
Cell impermeant
In cell impermeant molecules, the signal (neurotransmitter) can be contained in a lipid ____.
Vesicle
Cell impermeant molecule receptors must be on the cell _____.
Surface
3 examples of cell permeant molecules (2 unconventional neurotransmitters, 1 hormone)
Endocannabinoids
NO
Estrogen
Can cell permeant molecules be contained in a vesicle? Why or why not?
No- are lipid soluble so can pass through vesicle
Cell permeant molecules can bind receptors on the cell ___ or ____ the cell.
Surface
Inside
Cell associated molecules include adhesion molecules such as ____ or _____.
Integrins
Ephrins
Cell associated molecules can signal (uni-/bi-directionally). Why?
Bi-directionally
Molecules in both cells could be considered receptor or ligand
4 types of cellular receptors
Channel-linked receptors
Enzyme-linked receptors
G-protein coupled receptors
Intracellular receptors
Channel-linked receptors include the _____-_____ ____ channels and are gated by _____, or secreted molecules.
Ligand gated ion
Ligands
With enzyme-linked receptors, binding on the _____ side induces _____ change that activates ____ on the ____ side.
Extracellular
Conformational
Enzyme
Intracellular
Enzyme-linked receptors bind what 2 types of cell signaling molecules? What is an example of each?
Cell-impermeant molecules (neurotrophin)
Cell-associated molecules (integrins)
With G protein-coupled receptors, binding on the _____ side induces _____ change that enables association with ____ _____ on the ____ side.
Extracellular
Conformational
G proteins
Intracellular
G protein-coupled receptors usually bind ___ ____ molecules, but can bind other types of ligands.
Cell impermeable
Intracellular receptors bind only _____ _____ molecules because they are located only on the intracellular side.
Cell permeant
What are the best known type of intracellular receptors?
Estrogen receptors
What 2 types of cellular receptors are considered to be “typical” neurotransmitter receptors, and which 2 are not?
“Typical”: channel-linked, G protein-coupled
Not “typical”: enzyme-linked, intracellular
3 types of signaling
Synaptic
Paracrine
Endocrine
In which type of signaling are the cells located the closest to each other?
Synaptic
In synaptic signaling, the ligand can be how many of the 3 types of cell signaling molecules?
All (cell permeant, impermeant, or associated)
Most neurotransmitter signaling falls under which of the 3 categories?
Synaptic
In paracrine signaling, are the cells located close, intermediate, or far away from each other? This is because the cells are ____ each other, but don’t share an ____ ____.
Intermediate
Near
Active zone
3 examples of molecules that use paracrine signaling (2 are neurotransmitter types)
Hormones
Endocannabinoids
Neuropeptides
Paracrine and endocrine signaling can use either cell ___ or ___ molecules, but not cell ____ molecules for signaling.
Permeant
Impermeant
Associated
In which type of signaling are the cells the farthest away from each other?
Endocrine
In endocrine signaling, the signal travels through the ____ ____. What type of molecules are used in this type of signaling?
Blood stream
Hormones
Second messengers are (intracellular/extracellular) signaling molecules that are released by the cell in response to (intracellular/extracellular) signaling molecules, the first messengers.
Intracellular
Extracellular
Second messengers include _____, ____, and ____.
Nucleotides (ATP, etc)
Ions (Ca+2, etc)
Phospholipids (PIP2, etc)
Binding of a second messenger induces a conformational change in the ____, which is downstream in the signaling pathway. This could cause (activation/inactivation/both) of this molecule.
Effector
Both
In phosphorylation, ____ is used as the source of phosphate.
ATP
What is the name of the enzyme that takes the phosphate group off of ATP? What type of bond does it use to attach the phosphate to its target?
Kinase
Covalent
Phosphorylation of a target induces ____ change that (activates/inhibits/both) the target.
Conformational
Both
What is the name of the enzyme that breaks the covalent phosphate bond and removes the phosphate from the target, inducing a conformational change in the target?
Phosphatase
Phosphate groups are normally added to which 3 amino acids of a target protein?
Serine, threonine, tyrosine
Signal amplification: ____ (number) ligand(s) binding to a receptor activates (one/many) downstream effectors.
One
Many
2 types of GTP binding proteins (think number of subunits)
Heterotrimeric G proteins
Monomeric G proteins
Are the heterotrimeric or monomeric G proteins used more in neurotransmitter signaling? Which one plays a greater role in cell cycle?
Heterotrimeric
Monomeric
In a heterotrimeric G protein, are the subunits encoded by the same or different genes?
Different
Inactive heterotrimeric G proteins bind to (GTP/GDP).
GDP
Both heterotrimeric and monomeric G proteins bind to ____ to become activated and have _____ activity that enables them to hydrolyze ____ to ____.
GTP
GTPase
GTP
GDP
Hydrolyzing GTP to GDP turns a G protein ___.
Off
When ligand binds to a G protein coupled receptor (GPCR), a ____ change in the receptor occurs that enables interaction with a ____ _____. That interaction enables a ______ change to occur in the _____ subunit of that protein, causing it to exchange ____ for ___, which activates it. The activated subunit interacts with the ____ protein, which activates it. Next, the ____ ____ ____ (___) activates _____ activity of the activated subunit, which causes it to hydrolyze ____ to ____ and become inactivated.
Conformational G protein Conformational Alpha GDP GTP Effector GTPase Activating Protein (GAP) GTPase GTP GDP
What are the names of the 3 subunits in a heterotrimeric G protein? Which subunits are required for binding to the G protein coupled receptor? Which two have functions different from the third? Which subunit has GTPase activity?
Alpha, beta, gamma
All 3
Beta and gamma
Alpha
Can the G protein coupled receptor activate more than 1 G protein as long as the ligand is bound?
Yes
Is GDP removal from the G protein a slow or fast process?
Slow
Is adding GTP to the G protein a slow or fast process?
Fast
How does the activated G protein coupled receptor affect the rate of G protein activation?
Speeds it up
Trimeric and monomeric G proteins are only active when?
When bound to GTP
Each G protein coupled receptor binds how many type(s) of G protein?
1
Which is considered to be an amplification step: the neurotransmitter binding to receptor, or the receptor binding to G protein? Why?
Receptor binding to G protein
Receptor can activate multiple G proteins per neurotransmitter bound
What are the 3 types of heterotrimeric G proteins?
Gs, Gi, Gq
Gs and Gi trimeric G proteins act on the effector protein ____ _____. Which one triggers inhibition, and which one triggers stimulation?
Adenylyl cyclase
Gs- stimulation
Gi- inhibtion
Following binding to a Gs or Gi coupled receptor and activation of the corresponding G protein, adenylyl cyclase turns ____ into ____, which acts on ____ ____ ___, which _____ proteins.
ATP
cAMP
Protein kinase A
Phosphorylates
Gq trimeric G proteins (activate/inhibit) the effector protein _____ ____.
Activate
Phospholipase C
Following binding to a Gq coupled receptor and activation of the corresponding G protein, phospholipase C turns ______ into ____ and _____.
PIP2
DAG
IP3
In the Gq trimeric protein pathway, DAG acts on ____ ____ ____ and IP3 stimulates _____ release by binding to a ligand-gated ion channel. Release of this ion acts on ___ ____ ____ (same as above) and ____ ____ ___.
Protein kinase C
Ca+2
Protein kinase C
Calcium calmodulin kinase
Both the Gs and Gq trimeric G proteins _____ protein phosphorylation, whereas the Gi protein _____ it. In addition, the Gq protein activates ____-binding proteins.
Increase
Decreases
Calcium
With Designer Receptors Exclusively Activated by Designer Drugs (DREADDs), the (G protein coupled receptor/G protein) is mutated so that it cannot bind endogenous ligands. Instead, it binds the artificial ligand ____-___-____ (___). The (G protein coupled receptors/G proteins) still bind normally.
G protein coupled receptor
Clozapine-N-oxide (CNO)
G protein
A given neurotransmitter can bind (one/ more than one) type of G protein coupled receptor. In contrast, a G protein coupled receptor can bind (one/ more than one) type of trimeric G protein. The trimeric G protein can bind (one/any) G protein coupled receptor with the appropriate intracellular domain.
More than one
One
Any
A GTPase activating protein (GAP) activates the ___ activity of the ____ subunit of the trimeric G protein.
GTPase
Alpha
A GTPase activating protein (GAP) has what effect on the alpha subunit’s ability to interact with the effector protein? Why?
Prevents it
Turns off alpha subunit by inducing hydrolysis of GTP to GDP
How does the GTPase activating protein (GAP) moderate the effect of ligand binding to G protein coupled receptors? Can it turn off signaling even when ligand is still bound to the G protein coupled receptor?
Reduces
Yes
A GTP exchange factor (GEF) enables the ____ subunit of the trimeric G protein to exchange ___ for ____.
Alpha
GDP
GTP
A GTP exchange factor (GEF) has what effect on the alpha subunit’s ability to interact with the effector protein? Why?
Enables it
Turns on alpha subunit by replacing GDP with GTP
How does the GTP exchange factor (GEF) moderate the effect of ligand binding to G protein coupled receptors? Can it turn on signaling in the absence of ligand?
Increases
Yes
Both GTPase activating proteins (GAPs) and GTP exchange factors (GEFs) uncouple G protein ____ from ____ binding.
Signaling
Ligand
The G protein coupled receptor itself acts as a (GAP/GEF) because it activates the G protein.
GEF
Reduction of signaling by the alpha subunit of a trimeric G protein can be accomplished by increasing (GAP/GEF) activity and (GTPase activity/GTP binding).
GAP
GTPase activity
Increased signaling by the alpha subunit of a trimeric G protein can be accomplished by increasing (GAP/GEF) activity and (GTPase activity/GTP binding).
GEF
GTP binding
Dopamine has what 2 G protein coupled receptors? Which one couples to Gs and which one couples to Gi?
D1R (Gs)
D2R (Gi)
When dopamine binds to a D1 receptor, protein X is phosphorylated. Which kinase is likely phosphorylating protein X? (Think about adenylyl cyclase pathway.)
Protein kinase A
In the adenylyl cyclase pathway, _____ breaks down cyclic AMP.
Phosphodiesterase
Which is the most important neuronal second messenger?
Ca+2
5 neuronal second messengers
Ca+2 Cyclic AMP (cAMP) Cyclic GMP (cGMP) IP3 Diacylglycerol (DAG)
What are two plasma membrane-based sources of Ca+2?
Voltage-gated Ca+2 channels
Various ligand-gated channels
What are two endoplasmic reticulum-based sources of Ca+2?
IP3 receptors
Ryanodine receptors
6 intracellular targets for Ca+2
Calmodulin Protein kinases Protein phosphatases Ion channels Synaptotagmin Other Ca+2 binding proteins
2 plasma membrane-based removal mechanisms for Ca+2
Na+/Ca+2 exchanger
Ca+2 pump
1 endoplasmic reticulum based removal mechanism for Ca+2
Ca+2 pump
Organelle (in addition to endoplasmic reticulum) that is involved in removal of Ca+2
Mitochondria
Source of cAMP: ____ ____ acts on ____
Adenylyl cyclase
ATP
2 intracellular targets of cAMP
Protein kinase A
Cyclic nucleotide-gated channels
What enzyme is responsible for removal of cAMP?
cAMP phosphodiesterase
Source of cGMP: ____ ____ acts on ____
Guanylyl cyclase
GTP
2 intracellular targets of cGMP
Protein kinase G
Cyclic nucleotide-gated channels
What enzyme is responsible for removal of cGMP?
cGMP phosphodiesterase
Source of IP3: ______ ____ acts on _____
Phospholipase C
PIP2
Intracellular target of IP3 (molecule type, location)
IP3 receptors on endoplasmic reticulum
What type of enzyme is responsible for removal of IP3?
Phosphatase
Source of diacylglycerol (DAG): ____ ____ acts on _____ (same as for IP3)
Phospholipase C
PIP2
Intracellular target of diacylglycerol (DAG)
Protein kinase C
Removal of diacylglycerol (DAG): various ____
Enzymes
4 types of proteins regulated by binding Ca+2 and what they do
Protein kinase C (phosphorylates)
Calcineurin (phosphatase- dephosphorylates)
Calmodulin (Ca+2 buffering, activates CaMKII)
Calcium calmodulin kinase II (CaMKII; phosphorylates)
2 targets of CaMKII (talked about earlier in lecture; many more targets than just these 2)
GAPs
GEFs
cAMP and cGMP are both considered ____ _____. They target what type of channels? On which side of the channels do they bind? Both activate a protein _____.
Cyclic nucleotides
Cyclic nucleotide gated channels
Cytoplasmic side
Kinase
PIP2 is the precursor of both _____ and _____.
Diacylglycerol
IP3
PIP2 and diacylglycerol (DAG) are both located in the ____ ____. What enzyme breaks PIP2 down into DAG?
Plasma membrane
Phospholipase C
While PIP2 is located in the plasma membrane, IP3 is located in the _____. IP3 binds the IP3 receptor, a ligand-gated ion channel for what ion?
Cytosol
Ca+2
_____ (enzyme type) breaks IP3 into _____.
Phosphatases
Inositol
Most enzymes are regulated so that they have ____ or ____ forms. Why is this?
Active
Inactive
Easier to inactivate or activate enzyme than to synthesize it every time it is needed
Regulation of enzyme activity is usually accomplished by binding to ____ ____ and/or altering the _____ state of the enzyme.
Second messengers
Phosphorylation
Activating conformational change of an enzyme will separate its _____ and _____ domains/subunits.
Catalytic
Regulatory
What part of the enzyme has enzymatic activity? What part inhibits the enzyme?
Catalytic
Regulatory
Regulatory and catalytic parts of enzyme: domains of same protein, separate protein subunits, or either?
Either
Protein kinase A has how many regulatory subunits? How many catalytic subunits?
2
2
What molecule activates protein kinase A? How many molecules per regulatory subunit?
cAMP
2 molecules per subunit, 4 total
How is protein kinase A activated?
4 molecules of cAMP bind to regulatory subunits (2 per subunit), which triggers conformational change that activates protein kinase A
Ca+2 calmodulin kinase II (CaMKII) has how many regulatory domains? How many catalytic domains?
6
6
For protein kinase A and calcineurin, each subunit comes from a separate _____.
Protein
What 2 molecules activate CaMKII?
Ca+2
Calmodulin
In the absence of Ca+2 and calmodulin, what does CaMKII look like? After activation, how does its shape change?
Folded up
Opens up
How is CaMKII activated?
Ca+2 and calmodulin bind to CaMKII, causing a conformational change that opens it up and activates it
How many regulatory domains does protein kinase C have? How many catalytic domains?
2
1
What 2 molecules activate protein kinase C?
Ca+2
Diacylglycerol (DAG)
How is protein kinase C activated?
Ca+2 and DAG interact with regulatory domains (located near plasma membrane, since DAG is plasma membrane bound), which triggers conformational change that activates protein kinase C
MAP kinases are activated by _____, which involves covalently binding a _____ group from _____.
Phosphorylation
Phosphate
ATP
2 ways that MAP kinases are phosphorylated (and thus activated)
Auto-phosphorylation
Phosphorylation by other kinases
The phosphatase calcineurin requires which 2 molecules to become activated? What kinase is activated in a similar way?
Ca+2
Calmodulin
CaMKII
cAMP Response Element Binding (CREB) has what function?
Transcription factor
What effect does CREB have on transcription? (Increase, decrease, either)
Either increases or decreases
CREB is activated by ____ through many different ____. What is the name of the active form found in the nucleus that binds DNA?
Phosphorylation
Kinases
pCREB (phosphorylated CREB)
CREB can be activated through G-protein mediated activation of ____ ____, which activates ____, which activates ___ ___ ___, which phosphorylates CREB. CREB can also be activated by ____, which enters through ion channels and activates ____ ____ ____ or _____ ____, either of which can phosphorylate CREB.
Adenylyl cyclase cAMP Protein kinase A Ca+2 Calcium calmodulin kinase MAP kinase
Of the 4 types of cellular receptors, which one has direct phosphatase and kinase abilities?
Enzyme-linked receptors
In the G-protein pathway, what are the 3 amplification steps?
Receptor activates G protein
Effector protein activates second messengers
Later effectors (protein kinases, etc.) perform target action (phosphorylation, etc.)
(GAPs/GEFs) promote dissociation of G protein subunits, whereas (GAPs/GEFs) promote re-association of G protein subunits. (Remember which is associated with activation and which is associated with inactivation)
GEFs
GAPs
What kinase is active in long-term depression (LTD), and which is active in long-term potentiation (LTP)? These kinases phosphorylate which 2 receptors? What is the effect of phosphorylation in LTD and what is the effect of phosphorylation in LTP?
LTD: protein kinase C LTP: CaMKII AMPA, NMDA LTD: decreased depolarization LTP: increased depolarization
