Thursday, April 23, 2009

31.2) Distributed Brownian Motion Machinery: Clathrin Coated Pits

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Learn the particular kind of Brownian motion machinery that cells exploit to explore possibilities and make patterns and solve problems. show the mechanism of clathrin coated pits that cells use to ingest food packets.

some forms of endocytosis in cells is done as follows: receptor molecules randomly swim around on the cell membrane. when one bumps into the thing it's supposed to sense outside of the cell, it attaches, and rearranges it's butt sticking into the cell. clathrin molecules swim around just beneath the cell membrane inside. when one bumps into an activated receptor's butt it holds on with it's center while it holds out its 3 arms which are arranged symmetrically and bent INTO the membrane a little bit. well eventually another receptor swims by and bumps into the thing that's got to be brought into the cell, it activates and another clathrin attaches. the clathrins hold each other's arms. each molecule only "knows" about its neighbors. as more of this happens, aided by Brownian motion of all molecules involved, a cage is formed around a piece of cell membrane enclosing the stuff to be brought in and eventually pinches off. very clever. look:

Receptor-mediated endocytosis by clathrin-coated vesicles
By Dr Tony Jackson *

A review of how research into the components of the clathrin coat has provided insights into the operation of these molecular machines

mechanism of forming clathrin coated vesicles:

The clathrin machine is not like a computer program at all. the processing is totally distributed. furthermore I suspect we could isolate the molecules involved and get them to work without the whole live cell shebang. have to probably supply the proteins ready phosphorylated though.

why not call it a machine? what's your definition of a machine? something with gears, pulleys and integrated circuits? I think of machines as things you can understand by seeing how the separate parts interact.

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