明朝中后期正值世界地理大发现之时，世界贸易。()A.正确B.错误...

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明朝中后期正值世界地理大发现之时，世界贸易。()

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【多选题】How do the motor proteins kinesins and dyneins work?

The kinesins generally move toward the plus end of a microtubule (outward from the cell body); the dyneins move toward the minus end. Kinesins and cytoplasmic dyneins are generally dimers that have two globular ATP-binding heads and a single tail.

The heads of kinesin and cytoplasmic dynein interact with microtubules in a stereospecific manner, so that the motor protein will attach to a microtubule in only one direction.

The tail of a motor protein generally binds stably to some cell component, such as a vesicle or an organelle, and thereby determines the type of cargo that the motor protein can transport. Each of kinesins is thought to transport a specific set of vesicles, organelles, or molecules. In some cases, the tail of the kinesin binds directly to the cargo, while in other cases, different adaptor proteins allow the same type of kinesin to carry different cargos. Transport toward the minus end is mediated by cytoplasmic dynein, which generally uses adaptor proteins to interact with its selected cargo.

The globular heads of kinesin and dynein are enzymes with ATP-hydrolyzing (ATPase) activity. This reaction provides the energy for driving a directed series of conformational changes in the head that enable the motor protein to move along the microtubule by a cycle of binding, release, and rebinding to the microtubule. ATP hydrolysis and phosphate release by the rear motor head loosens its attachment to the microtubule. ADP release and ATP binding by the front motor head then cause a dramatic conformational change that flips the rear motor head to the front, thereby completing a single step.

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