Key Concepts of Section 18.4

• Kinesin-1 is a microtubule (+) end–directed ATP-dependent motor protein that transports membrane-bounded organelles (see Figure 18-19).

• Kinesin-1 consists of two heavy chains, each with an N-terminal motor domain, and two light chains that associate with cargo (see Figure 18-18).

• The kinesin superfamily includes motors that function in interphase and mitotic cells, transporting organelles and sliding antiparallel microtubules past each other. The superfamily includes one class, kinesin-13, that is not motile, but instead destabilizes microtubule ends (see Figure 18-20).

• Kinesin-1 is a highly processive motor because it coordinates ATP hydrolysis between its two heads so that one head is always firmly bound to a microtubule (see Figure 18-21).

• Kinesin-1 can exist in an inactive folded conformation or in a cargo-associated extended conformation (see Figure 18-22).

• Cytoplasmic dynein is a microtubule (−) end–directed ATP-dependent motor that associates with the dynactin complex and cargo adapters to transport cargo (see Figures 18-24 and 18-26).

• Kinesins and dyneins associate with many different organelles to organize their locations in cells (see Figure 18-28).

• Post-translational modifications of tubulin can affect the stability of microtubules and regulate their ability to interact with microtubule-based motors.