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Workin and Actin

Page history last edited by Joe Redish 7 years, 1 month ago

7.2.P2

 

Cells migrate for a large number of reasons.  For example, during development of organs and the nervous system, cells rearrange,  Here we zoom into the inside of one cell to study one of the main mechanisms of motion.

 

Cells migrate by assembling actin into mechanical filaments that push the leading edge of a cell forward.  Away from the leading edge of the cell, the actin filaments dissolve and the individual actin proteins are recycled and diffuse and are thus useable again at the leading edge.  A schematic of this process is shown below (from Dayel et al PLOS Biol (2004).  The grey line indicates the plasma membrane, the boundary of the cell.   Note that it is highlighted in the figure that the assembling filaments generate a force on the membrane

  

The process of assembly and disassembly of actin filaments is often called treadmilling since the filaments as they push the membrane forward also push themselves backward, in a very striking "retrograde flow" shown below, in a video (from Van Goor D, Hyland C, Schaefer A, Forscher P (2012). "The Role of Actin Turnover in Retrograde Actin Network Flow in Neuronal Growth Cones". PLOS ONE. DOI:10.1371/journal.pone.0030959)

Click on the "DOWNLOAD" tabe on TOP of the wiki to view:  The-Role-of-Actin-Turnover-in-Retrograde-Actin-Network-Flow-in-Neuronal-Growth-Cones-pone.003095.ogv

 

Discuss the following statements.  If a statement is true, explain why.  If it is not correct, discuss what foothold idea the statement violates.   If you are not sure, feel free to provide both sides of the argument. 

 

A)     The actin proteins do work

 

B)      The entropy of actin decreases near the plasma membrane as actin forms filaments but this is made up by an increase of entropy as the actin dissolves further behind.

 

C)      The internal energy of the cell decreases during this cell migration process

 

D)     The cell produces heat as well as work during the cell migration process

 

E)      The cell produces work, but does not generate heat since it is in thermal equilibrium with its surroundings  

 

 

W. Losert 2/10/13

 

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