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Intracellular transport is the movement of vesicles and substances within the cell. Eukaryotic cells transport packets of components (membrane‐bounded vesicles and organelles, protein rafts, mRNA, chromosomes) to particular intracellular locations by attaching them to molecular motors that haul them along microtubules and actin filaments. This method of tranport is often confused with intercellular transport, which deals solely with the movement of cargo between cells not the net movement within a cell. Since intracellular transport heavily relies on microtubules for movement, the components of the cytoskeleton play a vital role in trafficking vesicles between organelles and the plasma membrane. The cell is not a static structure; it is akin to a large city with an intricate highway system connecting one area to the next. In order to properly maintain cell growth utilization of these “cellular highways” is achieved through intracellular transport. Through this pathway it is possible to facilitate the movement of essential molecules such as membrane‐bounded vesicles and organelles, protein rafts, mRNA and chromosomes. In addition to the various organelles, the cytoskeleton plays a key role in intracellular transport by providing the mechanical support necessary for the cell to divide and facilitates movement. It is composed of actin, intermediate filaments and microtubules which each have a role in locomotion, intracellular transport of organelles, cell shape and chromosome separation. Intracellular transport is unique to eukaryotic cells because they possess organelles enclosed in membranes that need to be mediated for exchange of cargo to take place. Conversely, in prokaryotic cells there is no need for this specialized transport mechanism because there are no membranous organelles and compartments to traffic between. Prokaryotes are able to subsist by allowing materials to enter the cell via simple diffusion. Intracellular transport is more specialized than diffusion, it is a multifaceted process which utilizes transport vesicles. Transport vesicles are small structures within the cell consisting of a fluid enclosed by a lipid bilayer, that have the capacity to hold cargo. These vesicles will typically execute cargo loading and vesicle budding, vesicle transport, the binding of the vesicle to a target membrane and the fusion of the vesicle membranes to target membrane. To ensure that these vesicles embark in the right direction and to further organize the cell, special motor proteins attach to cargo-filled vesicles and carry them along the cytoskeleton. It is helpful to think of these vesicles as cars and the components of the cytoskeleton as the roadways they travel upon. The selectivity of these vesicles is a key component in keeping the cell organized, for example they have to ensure that lysosomal enzymes are transferred specifically to the Golgi Apparatus not to another part of the cell which could lead to deleterious effects. ==Fusion== Small membrane bound vesicles responsible for transporting proteins from one organelle to another are commonly found in endocytic and secretory pathways. Vesicles bud from their donor organelle and release the contents of their vesicle by a fusion event in a particular target organelle. The net movement of proteins from the Endoplasmic Reticulum (ER) to the Golgi Apparatus represents one form of intracellular transport through this mode of vesicle budding. Since the ER is the site of protein synthesis it would serve as the parent organelle and the cis face of the golgi, where proteins and signals are received, would be the acceptor. In order for the transport vesicle to accurately undergo a fusion event it must first recognize the correct target membrane then fuse with that membrane. This fusion event allows for the delivery of the vesicles contents mediated by proteins such as SNARE proteins.SNAREs are small, tail-anchored proteins which are often post-translationally inserted into membranes that are responsible for the fusion event necessary for vesicles to transport between organelles in the cytosol. There are two forms of SNARES, the t-SNARE and v-SNARE which fit together similar to a lock and key. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Intracellular transport」の詳細全文を読む スポンサード リンク
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