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Microtubule Based Movement
By V F Murphy,
05/12/2004
Cellular Motility is the movement of a cell, or the movement of environment past a cell. In simple unicellular organisms, the movement of cells through their environment is generally the focus, however, for larger more complex, multicellular organisms, the movement of the environment past the cell is more prevalent, such as the beating of cillia within the lung.
Cellular Motility can be movement of a cell through its environment, or the movement of environment through (or past) a cell
Becker et al
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Whilst there are a number of methods with which a cell may generate force, we will concentrate on force generation which involves the use of microtubles.
Kinesin and Dynein lie at the heart of
Microtubule-Based Movement. These are termed Microtubule Associated Proteins (MAPs). These motor MAPs attach both to intracellular components, and to microtubles (MTs), and by moving along the MT they are able to transport the intracellular components, which could be organelles, or vesicles, to where they are required. In this way, MAPs can be visualised as trains running along MT tracks.
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ATP powers the movement of Kinesin or Dynein (MAPs) along the Microtubles, to which is attached intracellular components
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Motility is driven by ATP (Adenosine-Tri-Phosphate), the hydrolysis of which acts through specific proteins to mediate movement. Dynein has been differentiated from kinesin based upon its direction of movement - kinesin moves away from the negative end of a MT, i.e. away from the MTOC or centrosome, and towards the distal portion, termed retrograde axonal transport. Dynein however moves in the opposite direction, acting to move items closer to the MTOC, termed anterograde axonal transport.
Dyein Decends toward the MTOC, wherease Kinesin Klimbs away from the MTOC
MedicalEngineer.co.uk
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In the case of neurons, clearly defined axons are characterised by bundles of MTs. Here it can be demonstrated that the combination of kinesine and dynein act to move proteins to the end of the axons, the synaptic knobs. In the case of the squid giant axon, this distance can be up to a meter - allowing for proteins to reach areas far from possible protein synthesis apparatus. This is known as fast axonal transport - a mechanism very similar to that which is generally accepted to be displayed within other cells.
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