cell adhesion Flashcards

1
Q

what is epithelia?

A

sheets of bound cells found in epithelial tissues

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2
Q

what is epical basal polarity?

A

something that epithelial cells have resulting from distribution of components

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3
Q

how are cells attached in the epithelium?

A

directly by cell-cell junctions

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4
Q

what are three main types of cell-cell junctions?

A

tight junctions, adherens junctions, gap junctions

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5
Q

what type of junctions are associated with actin cytoskeleton?

A

adherens junction

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6
Q

what is the main component of adherent junctions/

A

cadherin/catenin complex

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7
Q

what is caherin?

A

transmembrane protein belonging to cadherin superfamily (all have extracellular portions with cadherin domain)

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8
Q

what do cadherin domains do?

A

forms rigid unit joined to each other by hinges with Ca2+ ions bound (to prevent flexing)

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9
Q

are caherins homophilic or heterophilic?

A

typical cadherins are homophilic, atypical cadherins are heterophilic

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10
Q

what is the purpose of caherins?

A

mediate highly selective recognition (enabling cells to stick to similar cells and stay away form different cells)

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11
Q

what does assembly of strong cell-cell adhesions require?

A

changes in actin cytoskeleton

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12
Q

what do catenins do?

A

link classical cadherins to actin cytoskeleton

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13
Q

what is planar cell polarity?

A

collective alignment of cell polarity across tissue plane

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14
Q

what is required for selectively permeable epithelia

A

adjacent cells to be sealed together by tight junctions

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15
Q

how are tight junctions visualized?

A

freeze-fracture electron microscopy (seen as branching network of sealing strands that encircle apical end of each cell)

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16
Q

what are the main proteins forming strands of tight junctions?

A

claudins and related proteins occludins

17
Q

what do claudins do?

A

form selective channels allowing specific ions to cross tight junction barrier

18
Q

what are tight junctions in insects?

A

called septate junctions (organized differently)

19
Q

what are gap junctions?

A

clusters of channels to join two cells together

20
Q

what are gap junctions made of?

A

building blocks of two connexons or hemichannels (one from each cell)

21
Q

what are connexons or hemichannels made of?

A

formed from a complex of 6 connexin proteins

22
Q

when are connexins/innexins used?

A

vertebrate -> connexins
invertebrate -> innexins

23
Q

how big are gap junctions and why?

A

pore size ~ 1.4nm, allows exchange of inorganic ions and small molecules but NOT macromolecuels