cell adhesion Flashcards
what is epithelia?
sheets of bound cells found in epithelial tissues
what is epical basal polarity?
something that epithelial cells have resulting from distribution of components
how are cells attached in the epithelium?
directly by cell-cell junctions
what are three main types of cell-cell junctions?
tight junctions, adherens junctions, gap junctions
what type of junctions are associated with actin cytoskeleton?
adherens junction
what is the main component of adherent junctions/
cadherin/catenin complex
what is caherin?
transmembrane protein belonging to cadherin superfamily (all have extracellular portions with cadherin domain)
what do cadherin domains do?
forms rigid unit joined to each other by hinges with Ca2+ ions bound (to prevent flexing)
are caherins homophilic or heterophilic?
typical cadherins are homophilic, atypical cadherins are heterophilic
what is the purpose of caherins?
mediate highly selective recognition (enabling cells to stick to similar cells and stay away form different cells)
what does assembly of strong cell-cell adhesions require?
changes in actin cytoskeleton
what do catenins do?
link classical cadherins to actin cytoskeleton
what is planar cell polarity?
collective alignment of cell polarity across tissue plane
what is required for selectively permeable epithelia
adjacent cells to be sealed together by tight junctions
how are tight junctions visualized?
freeze-fracture electron microscopy (seen as branching network of sealing strands that encircle apical end of each cell)
what are the main proteins forming strands of tight junctions?
claudins and related proteins occludins
what do claudins do?
form selective channels allowing specific ions to cross tight junction barrier
what are tight junctions in insects?
called septate junctions (organized differently)
what are gap junctions?
clusters of channels to join two cells together
what are gap junctions made of?
building blocks of two connexons or hemichannels (one from each cell)
what are connexons or hemichannels made of?
formed from a complex of 6 connexin proteins
when are connexins/innexins used?
vertebrate -> connexins
invertebrate -> innexins
how big are gap junctions and why?
pore size ~ 1.4nm, allows exchange of inorganic ions and small molecules but NOT macromolecuels
