320SummerHomework6-answers - Cell Biology (BIO 320), Summer...

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Cell Biology (BIO 320), Summer 2008, Dr. Bushart Homework for quiz 6 1. Kinesin-14 walks towards the minus end of microtubules due to the arrangement of the two motor head-regions relative to one another. Would altering the relative positioning of the two head-regions of myosin II cause it to move towards the minus ends of actin? Explain. The directional movement of kinesins involves the coordinated movement of the motor domains, but the head domains of myosin II function independently from one another. The orientation of one head to the other should not impact the normal function of either. [To take this further, what process could you reverse to get the myosin to walk to the other end (even if it’s not exactly plausible to do so)? See end for answer.] 2. Crawling cells (lamellipodia-based) sometimes exhibit “ruffled” edges when they fail to properly attach to the substrate they have protruded over. Why would a failure in attachment result in the backward movement of the protrusion instead of the desired action of normal traction? The problem here is that forward movement of the lagging cell body requires that the myosin pulls on the established actin mesh. Normally, the lamellipodium extended forward through polymerization of the actin network at the leading edge. That still occurs in this case. What is missing is the connection of this new protrusion to the underlying substrate. This attachment gives an anchor for the myosin to pull against and the lagging cell body moves forward. If the new protrusion isn’t anchored, the
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This note was uploaded on 08/31/2009 for the course BIO 320 taught by Professor Staff during the Summer '08 term at University of Texas at Austin.

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320SummerHomework6-answers - Cell Biology (BIO 320), Summer...

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