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2 Movement

Figure 2.3: Motor proteins also transport cargo (organelles, chemical compounds) in the cell (adapted

from [9]).

[9] (Figure 2.3). There are different motor proteins for different cargo. Kinesins trans-

port intracellular organelles, move parts of the spindle during spindle formation, and

separate the DNA strands in mitosis and meiosis [14]. Dynein, on the other hand, is re-

sponsible for sliding microtubules against one another to generate ciliar and flagellar

movement (axonemal dyneins), or for most minus end-directed cargo transport along

microtubules (cytoplasmic dyneins).

In summary, transport occurs on microtubule tracks with motor proteins carrying

cargo and moving it in either direction. The kinesin and dynein motor proteins work in

a very similar manner as actin does during muscle contraction: the “stroke” that moves

the fiber forwards is performed by a stiff protein subunit that is powered by ATP. The

subunit then detaches and moves to the next site of the fiber, thus taking a “step” of

8–10 nm. This process proceeds across the fiber.