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What are epithelia?
Sheets of cells tightly bound together in epithelial tissues such as the gut lining and skin.
What type of polarity do epithelial cells establish?
Apical-basal polarity.
What types of junctions are important in epithelial cells?
Tight junctions, adherens junctions, and gap junctions.
What do adherens junctions associate with?
The actin cytoskeleton.
What is the main component of adherens junctions?
The Cadherin/Catenin complex.
What is the role of cadherins in cell adhesion?
Cadherins mediate selective recognition enabling similar cells to stick together.
What is required for cadherin-Cadherin binding?
Calcium (Ca2+) is required.
What happens when Ca2+ is removed from cadherins?
The hinges flex, making the cadherins structure floppy.
What distinguishes typical cadherins from atypical cadherins?
Typical cadherins are homophilic, while atypical cadherins are heterophilic.
What is the function of tight junctions?
To seal adjacent cells together, preventing molecules from leaking across the cell sheet.
What proteins form the strands of tight junctions?
Claudins and occludins.
What is the size of the pore in gap junctions?
About 1.4 nm.
What types of proteins form connexons in gap junctions?
Six connexin proteins.
What is the insect equivalent of tight junctions?
Septate junctions.
What is the role of gap junctions?
To connect cytoplasms of adjacent cells, allowing communication.
What are the two main types of proteins that form gap junctions in vertebrates and invertebrates?
Connexins in vertebrates and innexins in invertebrates.
What are gap junctions?
Clusters of channels that join two cells together, consisting of building blocks of two connexons or hemichannels, one contributed by each of the communicating cells.
What is a connexon or hemichannel formed of?
A complex of six connexin proteins.
What types of proteins form gap junctions in vertebrates and invertebrates?
Vertebrates form gap junctions with connexins, while invertebrates use innexins.
What is the pore size of gap junctions?
About 1.4 nm, allowing exchange of inorganic ions and small molecules, but not macromolecules.
What is the insect equivalent of tight junctions?
Septate junctions.
What proteins are involved in tight junctions?
Claudins.
What characterizes adherens junctions?
Strong cell-cell adhesion that is bound to the actin cytoskeleton.
What is the main component of adherens junctions?
The Cadherin/Catenin complex.
What is the role of cadherins in cell adhesion?
Cadherins mediate selective recognition enabling similar cells to stick together.
What is required for cadherin-Cadherin binding?
Calcium (Ca2+) is required.
What happens when Ca2+ is removed from cadherins?
The hinges flex, making the cadherins structure floppy.
What distinguishes typical cadherins from atypical cadherins?
Typical cadherins are homophilic, while atypical cadherins are heterophilic.
What do adherens junctions associate with?
The actin cytoskeleton.
