BIO130H1 Lecture 23: Junctions

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26 Mar 2019
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BIO130 Lecture 23 25/03/2019
Types of junctions
Anchoring junctions
Occluding junctions
Channel-forming junctions
Signal-relaying junctions
Remember epithelial cells are cells that line surfaces, cavities and organs
Polarized epithelial cells
Junctions are arranged in a specific order
o Other cells can have junctions
o They might not have all of them and they might not have them in this
specific order
Polarized epithelial cells ends are different
o All mature epithelial cells are polarized
1. Tight junctions
a. Epical most junction
b. Tight junctions are occluded junctions
i. Stop stuff from going in between cells
c. All around the region between two cells sealing strands
2. Adherens junctions
a. Anchoring junctions
i. Stick cells together
b. Form adhesion belt
c. Found below tight junctions
3. Desmosomes
a. Anchoring junctions at specific sports
b. Found below adherens junctions
i. More toward the basal side
4. Gap junctions
All present in epithelial cells
(first two hold the sheet of
cells together)
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a. Channel-forming junctions
i. Stuff is exchanged in between cells
b. Found below desmosomes
5. Hemidesmosomes
a. Anchoring junctions
i. Anchors the cell to the extracellular matrix
b. NOT half of desmosome
Tight junctions
Create a tight seal between cells
o Prevent mixing of the extracellular environments
Act as fences in the membrane
o Prevent mixing of membrane proteins
Apical membrane proteins
Basal membrane proteins
Claudin and occludin proteins form a seal
Transmembrane proteins
Extracellular domains
o Interact with the extracellular domains of the proteins in the neighboring
cell
o Occludin proteins only interact with occludin proteins
o Claudin proteins only interact with claudin proteins
Claudin
o Required for tight junction seals
o Functional proteins are required in both cells!
Tight junctions are dependent on adherens junctions
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