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Lecture 3

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University of Toronto St. George
Jennifer Harris

Tuesday, March 3, 2009 - This week were going to be discussing cell junctions & adhesion bw cells. - They connect cells together or they connect cells to the matrix that underlies cells. Mechanically attach cells to cells or the extracellular matrix Seal the contacts bw the cells Allow chemical or electrical signals to pass from cell to cell (through these channels) - Today well focus on anchoring junctions. - Anchoring junctions hold cells together mechanically it attaches them to one another or to the matrix. - On this diagram, hes drawn to scale a typical size of a mammalian cell, ~50 microns wide & the tiny little dotspeck is a 50 nm long cell adhesion molecule. How can these individual molecules deal with these relatively massive cells? - We heard about this a little bit when we talked about the actin cytoskeleton & how actin molecules, which are also very small, similar to the size in the diagram, we saw that they could impact cell structure by assembling huge networks inside the cell & pushing against the plasma membrane, pushing the plasma membrane outwards to change cell shape. Here that same principle applies. - These cell adhesion molecules, these tiny cell adhesion molecules, assemble larger complexes & these complexes have 2 features that overcome this challenge of size (as listed in the slide). - Diagram: Here is one single cell & here is a cell-cell adhesion complex these would be a large number of cell adhesion molecules clustered together in that complex & they connect to the cytoskeletal networks. - So you can follow protein-protein interactions bw the cell adhesion complex through the cytoskeleton to another cell adhesion complex through the cytoskeleton of that cell, through another cell adhesion complex & so on so you have a huge assembly of proteins within these cells supporting the tissue support. - How can clustering cell adhesion molecules increase the strength of
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