Epithelium Flashcards
occluding junctions are also called
tight junctions, or Zonula Occludens
occluding junctions forms a ring or circumferential band around the cell
serves as a diffusion barrier
outer leaflets of adjoining plasma membrane fuse
fusion occurs in band or belt like configuration around cell
the tight junction seal is created by two transmembrane proteins
occludins, and claudins, form a zipper seal
zonula occludens proteins
ZO-1, ZO-2, ZO-3
zonula occludens proteins interact with cytoskeleton actin filaments
ZO-1 and ZO-2 proteins are vulnerable for toxins and pathogenic virus
example is Cholera toxin, cytomegalovirus, dengue virus
Toxins produced by helicobacter pylori damage the occluding junctions of the gastric mucosa and cause leaking of HCL in stomach wall
leads to bleeding and peptic ulcers
blood brain barrier
occluding junction that prevents proteins in the circulating blood entering nerve tissue
zonula occludens restrict movement of lipid rafts
functions of zonula occludens
prevents molecules crossing the epithelium, prevent a paracellular pathway
functions of zonula occludens
restrict movements of membrane lipids and proteins at the apical domain into the lateral and basal domains
functions of zonula occludens
maintain two distinct membrane domains- Apical, and basolateral
Anchoring junctions have two types
zonula adherens and macula adherens (desmosome)
zonula adherens are
continuous band like adhesion
macula adherens or Desmosomes
localized spot adhesion
zonula adherens are formed by
binding of transmembrane proteins E-cadherins (epithelial cadherins) of neighboring cells
zonula adherens are calcium dependent
macula adherens or desmosomes
provide strong attachment to cells
macula adherens contains large proteins of the cadherin family such as
desmogleins, desmocollins
macula adherens have cytoplasmic ends of the proteins bind with plakoglobins
plakoglobins bind with desmoplakins
gap junctions or nexuses
channels on the lateral surface of adjoining cells
gap junctions
allow direct passage of signaling molecules from one cell to another
gap junctions consist of transmembrane channels called
connexons