9 Poisons, Drugs, and the Cytoskeleton CASE STUDY: Actin Dynamics and Cell Motil

Question

9 Poisons, Drugs, and the Cytoskeleton CASE STUDY: Actin Dynamics and Cell Motility The cytoskeleton plays a major role in both the organization of cell shape as well as with cell movement. Underlying these processes is the dynamic actin cytoskeleton that can be reorganized to control different processes. Cell movement is crucial to the functioning of many cell types, but cell motility is not always beneficial. For example, cell migration is a major step in metastasis of cancer from one place in the body to other places. In addition, many pathogenic bacteria co-opt the actin cytoskeleton during the infection process and utilize it to propel themselves through cells and into the adjoining cells, which is necessary to propagate the infection. Thus, understanding the basic molecular mechanisms of actin cytoskeleton function has implications in multiple physiological processes. Key to both of the above processes is the ability of the actin to polymerize at distinct places in the cell and produce force. Just like with dynamics of microtubules, the dynamics of the actin cytoskeleton can be followed using fluorescently labeled actin subunits. Below are a series of experimental data that can be used to interpret the dynamics of the actin filaments. Earlier in this chapter (Fig. 9.8) it was demonstrated that fluorescently labeled tubulin subunits in a microtubule could be bleached with a laser. An alternative method is that proteins can be injected into cells, and then a certain wavelength of light is shone on them to make them become fluorescent (photoactivatable). This process is illustrated in the figure below in which photoactivatable actin (PA- actin) is injected into cell and allowed to equilibrate into the actin cytoskeleton. Laser light is illuminated in a small box near the leading edge of the cell so that only a small number of the actin subunits are labeled. The subsequent cartoons illustrate the results of this experiment where the researcher follows the edge of the cell as well as the fluorescent bar. -Actin Filaments (Only leading edge shown) of Movement ta O: photoactivate actin filaments t-1, follow activated zone versus leading edge te 2 follow activated zone versus leading edge te3 follow activated zone versus leading edge

Explanation / Answer

Answer

1) actin polymerisation is occuring towards the leading edge or end of the moving cell

2) As actins are contractile protein, their polymerisation must occur at leading point of the cell so that large actin polymer form at at that point and contraction of that pulls the part of the cell behind it towards the direction of movement of cells

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