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22 Cards in this Set
- Front
- Back
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What are the ends of the actin filament? What is the fuel?
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Actin found in spine. Polarised:
Barbed end - addition of actin monomers. Pointed end - removal of monomers. ATP-dependant addition. Actin removed is ADP bound. |
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Give some properties of microtubules.
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Mostly found in dendrite. Also polarised: have a plus and minus end. In axons, all point the same way: plus side points towards the end (presynaptic terminal/growth cone), minus side always points to the soma. In dendrites this varies (but distal dendrites are more similar to axons). Use GTP hydrolysis to recruit dimers of alpha and beta tubulin to plus end. Tubulin in microtubule is tyrosinated, detyrosinated when detached. Can be quickly dismantled - 'catastrophe'. Microtubules under constant turnover.
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What are the two microtubule motors? Give their properties.
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Kinesins and Dyneins. Kinesins go to plus side (end), Dyneins go towards soma. Each molecule has 2 "hands", 2 "feet". Hands hold molecule, feet walk along the filament.
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What are the different types of kinesins called? What is different about them?
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KIFs. Different KIFs bind different cargos. Phosphorylation of KIF can lead to release, as can calcium elevation.
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What are the motors for actin? Describe a specific function.
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Myosin II, V, VI. II and V have 2 legs, VI has one but forms a dimer in order to 'walk'. Myosin V has been shown to be involved in vesicular trafficking. Involved in local transport from microtubules.
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Name drugs which stabilise/destabilise actin.
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Prolifin increases addition. Cytochalasin inhibits addition. Lactrunculin increases breakdown at pointed end.
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Name 2 actin arrangements.
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Actin bundles: linked by alpha-actinin.
Actin gels: linked by filamin. |
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What joins receptors to the cytoskeletion?
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PSD-95 joins AMPARs and NMDARs to the actin cytoskeleton.
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What is the effect of latrunculin on synapses?
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Increase in mEPSC frequency. This indicates that actin, rather than transporting vesicles to the active zone, is preventing vesicles from fusing with the membrane. Therefore when actin is destabilised, vesicles are more free to fuse with the active zone, leading to mEPSC frequency increase.
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Describe a hypothesis regarding actin and myosin at the presynaptic terminal.
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Myosin VI is highly present. Perhaps involved in increased recruitment of vesicles from the reserve pool to the active zone in evoked release. When vesicles are endocytosed, they are removed by myosin VI. Therefore actin inhibits spontaneous release, but aids evoked release.
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Where is actin most present?
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Dendritic spines.
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What is the stability of actin in spines?
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Fluorescent actin bleached in dendritic spines. This recovers on a minute time scale, indicating a constant, slow turnover of actin.
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How does actin change in plasticity?
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In LTD, actin decreases.
In LTP, actin increases. This increases the gain of the synapse by recruiting more channels. Myosin V is involved in this. |
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What are the AMPAR accessory proteins?
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TARPs. Transmembrane AMPAR regulatory protein. They are crucial for stabilisation and fusion on the postsynaptic membrane.
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What is the stability of AMPARs.
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At rest, there is constant recycling (endo/exo-cytosis) of AMPARs between the cytoplasm and membrane. Therefore there is a fast time constant for exocytosis and endocytosis, allowing fast modulation of receptor numbers.
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What are the two routes of AMPAR recycling?
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Fast: NMDA-dependant Ca2+ release causes endocytosis of AMPARS into an endosome, and then fast transport back to the surface.
Slow: New receptors formed, gradually make their way to PSD. |
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How specific is receptor delivery?
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Does not necessarily occur at the PSD: quantum dot labelling of individual receptors has shown that receptor movement is random. Outside the PSD movement is fast, inside the PSD movement is slow. Therefore on average sites with slow movement will have a higher concentration of receptors.
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How is actin linked to the membrane in the AIS? How is it organised?
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Through interaction with beta-IV spectrin - Ankrin-G. Organised in circles.
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Describe the role of actin at the AIS, with 2 experiments.
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Fluorescent labelling of channels at the AIS again showed random movement. However, there is a highly focussed distribution at the AIS. The membrane is therefore much less fluid at the AIS than other areas of the axon/dendrite. The low membrane mobility of the AIS is absent in immature neurons. Destabilisation of the actin cytoskeleton (latrunculin) greatly increased high motility in the AIS.
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What is the evidence for the presence of a cytosolic diffusion barrier?
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Diffusion of a protein of sizes 10-kD and 70-kD was compared in young neurones before and after formation of the AIS. In the immature neuron there was equal diffusion of both sizes. In the neuron with a developed AIS there was diffusion of the 10-kD but not the 70-kD protein. This suggests that there is a meshwork in the AIS which restricts the movement of larger molecules.
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Experiment on specificity of the diffusion barrier?
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Experiment: Does generation of (for example) KIF(5B-17) chimeras cause the KIF to change direction depending on which molecule is the 'feet'? 17 goes to dendrite, 5B goes to axon. Swapping KIFs allows a previously blocked NMDAR to travel through the AIS (seen with fluorescence). Therefore changing the KIF confers selectivity. KIF5B are able to cross AIS, KIF17 (dendritic) is unable. Not just about size. Thought to be due to large microtubule/actin network. This determines polarity of neuron.
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What is the importance of Ankrin G? What binds it?
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AnkG is restricted to the AIS in neurons. There is an AIS-targeting motif in the cytoplasmic loop between domains II and III of Na+ channels that binds to AnkG. Channels not anchored by AnkG are removed from the membrane by endocytosis. Silencing AnkG blocks the formation of the AIS.
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