Bipn 140 Midterm 2

Front 1

Describe the function of the following proteins in NT release. Synapsin and CaMKII

Back 1

CAMKII mobilizes synaptic vesicles from the reserve pool by phosphorylating synapsin and thereby undoing the link that synapsin provides between synaptic vesicles and the restraining actin cytoskeleton

Front 2

Describe the function of the following proteins in NT release. Synaptotagmin

Back 2

A synaptic SNARE that contains binding sites for calcium. When it binds calcium, it enables the SNARE complex to twist in a way that forces fusion of the SV and plasma membrane bilipid layers, causing the release of transmitter.

Front 3

Describe the function of the following proteins in NT release. Synaptobrevin

Back 3

This snare, embedded in the membrane of the synaptic vesicle, binds to the PM snares, keeping the vesicle docked for NT release

Front 4

What is SNARE assembly regulated by?

Back 4

SNAPs and NSF (proteins

Front 5

What happens when toxins cleave the SNARE proteins?

Back 5

it blocks NT release because the SNARE protein does not bind Ca2+, still other molecules must be responsible for Ca2+ regulation of NT release.

Front 6

What is the importance of CAMKII?

Back 6

It binds to calmodulin in the presence of Ca2+ to stabilize the unfolded state which can phosphorylate substrates.

Front 7

During signal transduction, what happens to the receptor if there is no ligand?

Back 7

The receptor is off (α/β/γ are bound together in an inactive state with GDP in bound state)
-adenylate cyclase(makes cAMP) is also off.

Front 8

During signal transduction what happens when ligand binds to receptor?

Back 8

Causes receptor to change conformation--> attracts α subunits of G protein--> α subunit exchanges GDP for GTP and dissociates from β/γ--> α subunit conformation and binds to adenylate cyclase, activating it--> adenylate cyclase turns ATP into cAMP (2nd messenger).

Front 9

How do you reverse the signal transduction pathway?

Back 9

1. α subunit cleaves GTP to GDP--> α subunit dissociates from adenylate cyclase, turning it off--> α binds to β/γ--> signal is off

Front 10

Why is there a need for 2nd messengers and G proteins?

Back 10

for amplification

Front 11

What does cAMP do?

Back 11

turns on kinase which causes glycogen phosphorylase to phosphorylate itself and become active, therefore, creating glucose.

Front 12

How do you reverse the signal from adrenaline?

Back 12

1. Alpha hydrolyzes GTP to GDP

2.Active receptor (ligand bound), is than inactive, the receptor becomes desensitized.

3. cAMP is degraded to 5' AMP by cAMP phosphodiesterase

4. cAMP activates PKA which phosphorylates target proteins, but protein phosphatase dephosphorylates protein and target proteins are converted back to original form.

Front 13

What is the signal transduction for adrenaline?

Back 13

1. no ligand, G proteins and AC is off

2. Adrenaline (1st messenger, ligand) binds to B-adrenergic receptor. the receptor has affinity for alpha subunit, which causes it to exchange GDP for GTP. This causes alpha to leave B/y and leads to a conformational change

3.alpha-GTP activates AC and AC concerts ATP to cAMP

4.alpha cleaves GTP to GDP, which reverses the conformational change and alpha dissociates from AC. AC turns off and alpha associates with B/y

Front 14

What does G stimulatory do?

Back 14

stimulates AC (cholera toxin changes the alpha subunit so that it is always bound to GTP

Front 15

What does phospholipase C do?

Back 15

PLC cleaves PIP2 into (DAG) and (IP3).

*PIP2 is a special rare phospholipid used for cell signaling.

-DAG is hydrophobic so stays in PM
-IP3 is hydrophilic so it is in the cytoplasm.

Front 16

When IP3 binds what happens?

Back 16

it opens the channel, and Ca 2+ rushes out of the ER into cytoplasm.
-so before the signal [Ca2+]=10^-7 M and
-after the signal [CA2+]=10^-5 M

Front 17

What is the affect of the Ca 2+ released into the cytoplasm by IP3?

Back 17

Ca2+ activates Kinases.
1. 4 calcium binds to calmodulin, and creates a calcium/calmodulin complex
2. binds to calcium/calmodulin dependent protein kinase (CAM kinases)
3. phosphorylates specific target proteins and targets become activated or inactivated

Front 18

What does DAG do?

Back 18

DAG acts to bind protein kinase c (PKC) to the membrane and activate its kinase activity. results in phosphorylation of specific targets.

Front 19

Describe the function of the following proteins in NT release. Syntaxin and SNAP-25

Back 19

Can form macromolecular complex that spans the two membranes, thus bringing them into close apposition. Such arrangement binds the snares of the synaptic vesicle, keeping it docked for NT release

Front 20

What does clathrin do and how does it work with dynamin?

Back 20

Clathrin is forcing the membrane to bend, dynamin causes it to pinch/cut off, and then binds to actin.

Front 21

What is the difference between Ionotropic and metabotropic receptors?

Back 21

1. Ionotropic NT receptors are ligand-gated ionic channels. They are made of transmembrane proteins that only allow specific ions to cross through the internal pore

2. Metabotropic NT receptors are G protein0coupled receptors that can activate downstream signaling. They amplify the signal, exert multiple different actions in response to activation, and offer specificity via compartmentalization of the downstream signaling machinery.

Front 22

Suppose a presynaptic neuron were to fire, release glutamate, and elicit an EPSP at the same time as the PSP shown above. Further, suppose that, normally, the EPSP depolarizes the cell by 10 mV when acting alone. Would you expect the postsynaptic neuron to reach threshold when this EPSP is combined with the PSP above?

Back 22

No. One would expect perhaps a minor depolarization on top of the IPSP
shown above, but the magnitude of the additional depolarization due to the EPSP
would not be 10 mV due to the countercurrent produced by the ions that are responsible for the IPSP. That is, this is not simple summation, rather the IPSP
would in effect subtract from the depolarization elicited by the EPSP. The IPSP here is mediated by an outward flowing ICl- -> the exit of negative ions makes the inside of the cell a little more positive; how positive? only up to -50 – more positive than that and the Cl- will start flowing in again in order to keep the cell at it’s Eion. When glutamate is released at the same time, glutamatergic receptors allow Na+ to enter, but only a few channels are open. When the weak, inward INa+ tries to depolarize the cell (trying to reach its own ENa of +50), the ICl- will respond by driving Cl- inside the cell, making it more negative – an inward countercurrent. How could the excitatory current overcome the inhibitory current? The release of more glutamate would result in the opening of more Na+
channels, strengthening the INa until it is sufficient to overcome ICl- and reach threshold.

Front 23

What happens when the NMJ is bathed in a solution that has low [Ca2+]?

Back 23

When the neuromuscular junction is bathed in a solution that has a low [Ca++], stimulating the motor neuron evokes EPPs whose amplitudes are reduced to about the size of MEPPs.

Front 24

What is the usual means of eliminating muscle contractions?

Back 24

is either to lower Ca++ concentration in the extracellular medium or to partially block the postsynaptic Ach receptors with the drug curare. Lowering the Ca++ concentration reduces NT secretion, thus reducing the magnitude of the EPP below the threshold for postsynaptic AP production and allowing it to be measured more precisely. As you see, stimulation of the motor neuron produces very small EPPS that fluctuate in amplitude from trial to trial.

Front 25

What is spatial summation?

Back 25

two action potentials from two different synapses add together.

Front 26

What is temporal summation?

Back 26

two action potentials that come right after one another from one neuron in a rapid succession. The two EPSPs adds together

Front 27

Define quantal release. What physical structure is thought to correspond to a quantum?

Back 27

In response to depolarization, NT’s are released into the synapse in multiples of
individual-unit fixed amounts of NTs. The smallest unit is one quantum of NTs.
Individual synaptic vesicles each contain one quantum of NTs and are released in
large quantities following depolarization --> 1 quantum per vesicle exocytosed yields
quantal release of NTs.

Front 28

What is LTP?

Back 28

Stands for long-term potentiation, meaning a long-lasting increase in the size of the EPSP

Front 29

How can you induce an LTP?

Back 29

You stimulate the presynaptic neuron 2 times in close succession with a tetanic stimulus of 100 Hz for the duration of 1 second each time

Front 30

What is meant by LTP being pathway-specific? Given this pathway-specific feature of LTP, how can heterosynaptic LTP be induced?

Back 30

It is the phenomenon where you get an LTP at a neighboring synapse can be explained by looking at the activity of that synapse. If the synapse is also being stimulated at the same time that we are inducing an LTP in another close synapse you will have an LTP at both synapses.

Front 31

Explain how NMDA receptors work and what they contribute to LTP.

Back 31

There are 3 conditions that need to be met for NDMA receptors to activate. Glutamate (agonist) and glycine (co-agonist) need to be present as well the Mg2+ block which is voltage-dependent has to be relieved. Once NMDA receptors activate, they let in Ca2+ to flow in to the postsynaptic cell and Ca2+ activates Protein Kinase C as well as Ca2+/Calmodulin kinase II and these two kinases activity leads to inserting more AMPA receptors into the postsynaptic membrane.

Front 32

What are the 3 advantages of IC second messenger signaling pathways?

Back 32

1. Molecular pathway from receptor to a target: provides access to the target (rather, say, than a wave of depolarization or an influx of calcium that unspecifically will affect anything voltage gated in the area)

2.Amplification: one molecule of glutamate can turn on several receptors, which will release, for example, a G protein, which can individually activate several kinases, which can stay on for a while and phosphorylate several targets

3. Compartmentalization: one can have signal transduction in one part of the cell, w/o turning on the rest of the cell; can keep the signaling pathways physically separate, for example, restricting effects to one single synapse while leaving the synapses of the rest of the cell alone)

Front 33

Describe 4 sources of intracellular calcium, and 4 ways in which calcium is absorbed or removed from the cell.

Back 33

Sources of intracellular calcium: coltage gated calcium channels, ligand gated calcium channels, IP3 receptors on mitochondria, ryanodine receptors on mitochondria.

Calcium is removed or absorbed by: Na+/Ca2+ exchangers on cell membrane, Ca2+/H+ pumps on the cell membrane and mitochondria, Ca2+ binding buffer proteins, simple absorption by the mitochondria.

Front 34

What happens when AMPA receptors are tetanically stimulated?

Back 34

Mg2+ blocking the NMDA receptor is removed. They provide a persistent depolarization that repels the Mg2+ and all Ca2= to flow through the NMDA receptors and cause intracellular changes below.

Front 35

True or False, second time you stimulate the presynaptic membrane, you get a bigger second PSP due to the piling up of calcium.

Back 35

True, this causes a higher probability of vesicles coming out.

Front 36

What happens when their is a big interval between the pulses (post-tetanic potentiation)?

Back 36

The bigger the interval between the pulses the more calcium cleared out and the less the facilitation. Depends on how quickly the terminal can get rid of the previous calcium.

Front 37

One form of short-term synaptic plasticity involves that of normal calcium. What happens?

Back 37

Normal calcium leads to a tetanus which causes a strong and fast depression because of the use up of the vesicle pool faster than you can use it and when you release it it goes back to normal

Front 38

What happens if you decrease the calcium concentration for short-term synaptic plasticity?

Back 38

If you really decrease the [Ca2+] you keep getting a release of vesicles and neurotransmitter, but you don't get that depression because even though you're firing very fast, you never sufficiently deplete those release sites.

Front 39

What happens when you release fewer vesicles?

Back 39

The fewer vesicles that you release from the presynaptic terminal, the less the depression

Front 40

LTP's are pathway specific so if tetanus occurs in one synapse and not in the other, what will happen?

Back 40

Tetanus in one synapse will result in LTP only at that synapse, not all the synapses in the area (even the ones that are really close by). So if pathway 1 is tetanized and gets stimulated and stays up there for about an hour, but pathway 2 never got anything, stays always about the same.

Front 41

What does state-dependent mean?

Back 41

pairing of pre and post synaptic events which must have postsynaptic depolarization while stimulating the EPSP. If the schaffer collateral fired but it wasn't strong enough to depolarize the membrane, no LTP.

Front 42

What is the role of calcium in molecular mechanisms of LTP?

Back 42

Ca2+ is needed in the postsynaptic cell. Put Ca2+ chelater BAPTA (a very good chelator of calcium) and it will block LTP formation.

Front 43

When NMDA receptors are blocked with APV then no LTP occurs. How does it affect AMPA's or GABA?

Back 43

Doesn't block AMPA's or GABA or other; quite specific

Front 44

What are the three conditions for activation of NMDA receptors?

Back 44

1. Glutamate
2. Glycine (co-agonist)
3. Relieve the magnesium block; voltage dependent.

Front 45

What is the postsynaptic mechanism of LTP?

Back 45

1. Ca2+ entry activates postsynaptic CaMKII and PKC
2. recruit intracellular AMPA receptors which move to surface at postsynaptic sites

Front 46

What is the role of Mg2+ in regards to NMDA receptors?

Back 46

Mg2+ blocks NMDA receptors. It is removed when AMPA receptors are tetanically stimulated they provide a persistent depolarization that repels the Mg2+ and allows calcium to flow through the NMDA receptors and cause intracellular changes below.

Front 47

Name three major categories of receptors and provide an example of each, explaining which feature is characteristic of each class

Back 47

-Surface receptors activated by CELL IMPERMEANT AGONISTS: Examples include ligandgated ion channels, G protein-coupled receptors, and enzyme-linked receptors (receptor protein kinases), all of which have EXTRACELLULAR surface BINDING SITES for specific ligands. NOTE: enzyme-linked receptors have external binding sites but INTERNALLY-bound enzymes
(kinases)
-Surface receptors activated by CELL ATTACHED (OR TRANSMEMBRANE) AGONISTS: These receptors activate only in close proximity (or direct contact) with adjacent cells. Examples include EPHRIN, integrins, and NCAMS.
-Intracellular receptors activated by CELL PERMEANT AGONISTS: Examples include numerous hydrophobic molecules such as steroid and thyroid hormones, which have the ability to freely diffuse through the plasma membrane and bind to intracellular targets

Front 48

What are the 3 main purposes of signal transduction?

Back 48

i) to provide a molecular pathway from receptor to target

ii) amplification: to increase the molecular response possibly by orders of magnitude Starting Material Acetyl CoA + Choline Glutamine Glutamate Enzyme Responsible for synthesis Choline acetyltransferase Glutaminase Glutamic acid decarboxylase Neurotransmitter Acetylcholine Glutamate GABA Vesicle Pump VAChT VGLUT VGAT Enzyme Responsible for break down acetylcholinesterase Glutamine synthase None. Recycled as GABA

iii) compartmentalization: to separate downstream signals and allow them to exert specific
influences in various locations

Front 49

Indicate the three most common categories (examples) of second messengers

Back 49

i) Ca++
ii) cyclic nucleotides (such as cAMP)
iii) diacylglycerol (& IP3)

Front 50

What is LTP?

Back 50

Stands for long-term potentiation, meaning a long-lasting increase in the size of the EPSP.

Front 51

How can you induce an LTP?

Back 51

You stimulate the presynaptic neuron (e.g. the CA3) 2 times in close succession with a tetanic stimulus of 100 Hz for the duration of 1 second each time

Front 52

Define PSD95.

Back 52

a scaffold protein that crosslinks and anchors various players (receptors, second messengers) that are desired at the postsynaptic membrane

Front 53

Define “calcium bottle”

Back 53

The calcium that enters a dendritic spine will stay sequestered at that spine, although the current
may be able to leave and affect other synapses. (the result is a high, local concentration at a very
specific compartment) This can be visualized through calcium fluors that light up in the presence
of calcium.

Front 54

List 4 functions of glia that demonstrate their involvement in neuronal signaling. Which type of glia does this?

Back 54

Glial Astrocytes perform the following:

Recycle NTs
Receive synaptic input
Release NTs (ex. glutamate)
Release “synaptogenic components,” compounds that are used in generating synapses

Front 55

(a) What compound can be produced from arginine that can exert retrograde signaling at synapses? How can it do this, i.e. what unique physical feature does the component have and how does that help? (b) Name another class of retrograde signaling compounds at synapses.

Back 55

a) NO synthase converts Arginine into citrulline and the transmitter, Nitric oxide (NO), which is unique because it occurs in the gaseous phase and can diffuse out of the cell through the plasma membrane, as illustrated in Figure 6.2.

b) Endocannabinoids