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BIO230 Part.2 Exam Note (with lab notes).docx

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University of Toronto St. George
Tony Harris

Lecture 1Clathrin COPI COPII drive vesicle invagination events o Rmb they transport cargos from eg ER to Golgi by forming a bud on the ER membraneSignaling lipids PIPs o Each PI can be modified by kinasephosphatase to generate different PIPs they go to specific locations in the cell and bind with specific proteinsRab GTPase will be brought to specific places o Rab11recycling endosomes o Rab5Aplasma membrane clathrincoated cesicles early endosomes o Rab7late endosomeRabGDP with its amphoipathic helix inside are recruited to specific membranes by Rab GEFs Rab GEF then exchange the GDP to GTP activating Rab GTPase now its amphipathic hexlis is exposed The Vsnare on the vesicle which has RabGTP will tether with Tsnare on the target membrane At the same time Rab effector tethering protein on the target membrane will also react with RabGTP and bring the vesicle closer to the membrane for more efficient snare protein interaction Vesicle then fuses into the membrane and release cargoSignaling lipids PIPs will also help activate the Rab effector proteinAll together they help direct the vesicle with its protein to specific placesLecture 2Microtubules are polarized from subunits to protofilament to networkEach protofilament is made up of tons of heterodimerstublin tublin They are the subunits and they are polarized ends are differentve endve end They only form a protofilament when GTP is bound When GDP is bound the microtubule starts to deformA centrosome contains 2 centrioles in the centre with tublin nucleation site on the surface tublin ring complex tublinaccessory proteins will bind to ve end of the protofilaments and start forming microtubules 13 protofilaments1 microtuble So they ve end is facing outside and growing away from the nucleation siteMicrotubules show dynamic stability which they grow and shrink instead of being constantGrowing microtubules have a GTP cap Its composed of heterodimer bounded to GTPGfrom that can protect them from being deformed The new heterodimer GTP will be added and the original ones will be hydrolyzed GDP so the heterodimer is now in Tform If GTP hydrolysis is faster than subunit addition then protofilament will start falling apartcatastrophe If GTP cap is added then the protofilament will be rescued and start growing againBecause the centrosome is often close to the nucleus so the ve end of the microtubule is close to nucleus too This makes them able to form a coordinate system inside the cellThere are 2 types of motor 1 Dynein 2 Kinesin Dynein moves to the ve end back to nucleus and kinesin moves to the ve end They carry the cargo vesicles with proteins with them and they drag the cargo across the cell along the microtubules Microtubules help position Golgi bc Glogi is seen to be close to the nucleus So Dynesin is responsible it moves the Golgi towards the nucleus moving towards the ve endThe African fish can change their skin colour depending on which motor is dominant Kinesin and dynein compete for melanosome filled with black pigment If it wants to be white the giant cell will inhibit kinesin and dynein will move all the melanosome towards to ve end nucleus so you get little black dots When it wants to be black both kinesin and dynein are activated so they move melanosomes all over the place and thus the fish appears blackActin cytoskeleton also plays important role in organizing cell structure and controlling cell behaviourActin cytoskeleton is also polarized from subunit to filaments to networkIt has a monomer subunit 1 actin molecule Actin monomers are polarized They bind with ATP and assemble on top of each other to form a polarized filament ActinATP will be hydrolyzed to ActinADP this will decrease affinity of binding to neighbouring subunits and cause dissociation If the rate of addition of ActinATP is faster than the rate of removal of ActinADP a relatively stable cap of ActinATP subunits can be formedWhen the rate of addition and removal is about the same this will cause treadmilling This length of the filament will stay about the sameARP complex is activated by binded with Arp3 Arp2 and other proteins They nucleates actin filaments by stabilizing the ve end So now the ARP complex can be added anywhere along the filament and form a polarized 2D networkEven though actin filaments are treadmilling without traction the grip on the floor they cant push themselves forward And this traction is provided by stationary anchors which anchors to the extracellular matrix eg Basal laminaIntegrin proteins connect the actin filament to the extracellular matrix molecules They are transmembrane heterodimerschain chain that grip onto the extracellular matrix proteins It is linked to the actin cytoskeleton via adaptor proteinsMacrophages use actin polyermization to chase after bacteria When signal changes direction the actin filaments can disassemble and reassemble so they can chase in the right directionLecture 3Cells are organized as epithelial tissue or connective tissue The epithelial tissue are connected by celltocell cytoskeletal filament mechanical stresses are transmitted via these cytoskeletal filaments It forms our skin and coats our organs and right under it theres the basal laminar which counts as extracellular matrix Connective tissues cells eg Muscle cells neurons are dispersed throughout the extracellular matrix providing the overall structure of the cellEach epithelia cell might have micro villi and another layer of epithelia cell at the bottom coating the organ In bw that you have connective tissueThere are junctional complexes throughout the epithelial structure o Occluding junctionEg Tight junction claudinsThey dont let anything pass thru o Cellcell anchoring junctionEg Adherens junction cadherinsThey connect actin filament bundles from one cell to anotherEg Desmosoaml junction cadherins o Channelforming junctionEg Gap junctionAllows the passage of small water soluble molecules from cell to cellAdherens junctions form strong adhesion belts composed of actin filament that link neighbouring cells together to form epithelia There are actin filaments inside the microvillus as well Cadherin clusters are located in bw 2 epithelia cells and they mediate the adhesion by hemophilic interactions bw same type of cadherin proteins There are many different types of cadherin proteins only the same type can interact with each other These cadherin proteins are transmembrane proteins their Nterminus are interacting with each other and Cterminus is inside the cell The interaction bw Nterminus are kept rigid by the presence of Ca2 Their Cterminus are linked to actin filament by some other proteinsAdheren junction function tumour suppression o Cadherinns are tumour suppressor
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