Formation and transport Vesicle (biology and chemistry)

1 formation , transport

1.1 vesicle coat , cargo molecules
1.2 vesicle docking
1.3 vesicle fusion
1.4 in receptor downregulation
1.5 preparation

1.5.1 isolated vesicles


1.6 artificial vesicles

formation , transport

some vesicles made when part of membrane pinches off endoplasmic reticulum or golgi complex. others made when object outside of cell surrounded cell membrane.

vesicle coat , cargo molecules

the vesicle coat collection of proteins serve shape curvature of donor membrane, forming rounded vesicle shape. coat proteins can function bind various transmembrane receptor proteins, called cargo receptors. these receptors select material endocytosed in receptor-mediated endocytosis or intracellular transport.

there 3 types of vesicle coats: clathrin, copi , copii. various types of coat proteins sorting of vesicles final destination. clathrin coats found on vesicles trafficking between golgi , plasma membrane, golgi , endosomes , plasma membrane , endosomes. copi coated vesicles responsible retrograde transport golgi er, while copii coated vesicles responsible anterograde transport er golgi.

the clathrin coat thought assemble in response regulatory g protein. protein coat assembles , disassembles due adp ribosylation factor (arf) protein.

vesicle docking

surface proteins called snares identify vesicle s cargo , complementary snares on target membrane act cause fusion of vesicle , target membrane. such v-snares hypothesised exist on vesicle membrane, while complementary ones on target membrane known t-snares.

often snares associated vesicles or target membranes instead classified qa, qb, qc, or r snares owing further variation v- or t-snares. array of different snare complexes can seen in different tissues , subcellular compartments, 36 isoforms identified in humans.

regulatory rab proteins thought inspect joining of snares. rab protein regulatory gtp-binding protein , controls binding of these complementary snares long enough time rab protein hydrolyse bound gtp , lock vesicle onto membrane.

vesicle fusion

vesicle fusion can occur in 1 of 2 ways: full fusion or kiss-and-run fusion. fusion requires 2 membranes brought within 1.5 nm of each other. occur water must displaced surface of vesicle membrane. energetically unfavorable , evidence suggests process requires atp, gtp , acetyl-coa. fusion linked budding, why term budding , fusing arises.

in receptor downregulation

membrane proteins serving receptors tagged downregulation attachment of ubiquitin. after arriving endosome via pathway described above, vesicles begin form inside endosome, taking them membrane proteins meant degradation; when endosome either matures become lysosome or united one, vesicles degraded. without mechanism, extracellular part of membrane proteins reach lumen of lysosome , part degraded.

it because of these vesicles endosome known multivesicular body. pathway formation not understood; unlike other vesicles described above, outer surface of vesicles not in contact cytosol.

preparation
isolated vesicles

producing membrane vesicles 1 of methods investigate various membranes of cell. after living tissue crushed suspension, various membranes form tiny closed bubbles. big fragments of crushed cells can discarded low-speed centrifugation , later fraction of known origin (plasmalemma, tonoplast, etc.) can isolated precise high-speed centrifugation in density gradient. using osmotic shock, possible temporarily open vesicles (filling them required solution) , centrifugate down again , resuspend in different solution. applying ionophores valinomycin can create electrochemical gradients comparable gradients inside living cells.

vesicles used in 2 types of research:

to find , later isolate membrane receptors bind hormones , various other important substances.
to investigate transport of various ions or other substances across membrane of given type. while transport can more investigated patch clamp techniques, vesicles can isolated objects patch clamp not applicable.

artificial vesicles

phospholipid vesicles have been studied in biochemistry. such studies, homogeneous phospholipid vesicle suspension can prepared extrusion or sonication, injection of phospholipid solution aqueous buffer solution membranes. in way aqueous vesicle solutions can prepared of different phospholipid composition, different sizes of vesicles.