Motor proteins are generally considered to move cellular components along microt

Question

Motor proteins are generally considered to move cellular components along microtubules. However, some kinesin family motors may have other functions as described below. a) In one set of experiments, microtubules were observed in a microscope chamber in which the solution could be rapidly exchanged. Part (a) of the accompanying figure depicts the effect on microtubule length as a function of time when the tubulin and buffer in the chamber were replaced first by an identical tubulin and buffer solution and then by buffer alone. Part (b) depicts the results when the tubulin and buffer solution in the chamber was replaced with a solution containing tubulin and the M-typc kinesin motor protein Kin I. What conclusions can you draw from these experiments? b) In another assay, taxol-stabilized microtubules were incubated alone (Ctrl), with kinesin heavy-chain (KHC) and ATP, with Kin I and ATP, or with Kin 1 and AMPPNP, and then centrifuged to pellet polymerized tubulin. Supernatant (s) and pellet (p) fractions were then separated by SDS-PAGE. and the gel was stained to reveal the position of tubulin, as shown in part (c). What conclusions can you draw from these experiments? What is the significance of the nucleotide present for Kin I activity? Would you expect ATP to be present in the experiments depicted in part (b) of the figure? Why or why not? c) Similar results to those shown in part (c) were also obtained when GMPCPP, a nonhydrolyzable GTP analog, was used to assemble stabilized microtubules. What docs this result suggest about the action of Kin I?

Explanation / Answer

Motor proteins are generally considered to move cellular components alongmicrotubules. However, some kinesin family motors may have other functions asdescribed below.a.In one set of experiments, microtubules were observed in a microscope chamber inwhich the solution could be rapidly exchanged.

Part (a) of the accompanying figuredepicts the effect on microtubule length as a function of time when the tubulin and bufferin the chamber were replaced first by an identical tubulin and buffer solution and then bybuffer alone.

Part (b) depicts the results when the tubulin and buffer solution in thechamber was replaced with a solution containing tubulin and the M-type kinesin motorprotein Kin I

What conclusions can you draw from these experiment

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In another assay, taxol-stabilized microtubules were incubated alone (Ctrl), withkinesin heavy chain (KHC) and ATP, with Kin I and ATP, or with Kin I and AMPPNP,and then centrifuged to pellet polymerized tubulin. Supernatant (s) and pellet (p) fractionswere then separated by SDS-PAGE, and the gel was stained to reveal the position oftubulin, as shown in the figure below What conclusions can you draw from these experiments?

Answer

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