Cell Junctions Flashcards
What determines the function of a protiens
It’s properties and interactions in junctions
What are the three membranes in the epithelium
Basal
Apical
Lateral
What is the apical
Basal
Lateral
Basal lateral
Top of cell facing lumen
Basal bottom (attached to ECM)
Side
Bottom and side
What special about the membranes of a polarized cell
It has a different apical membrane than its basal membrane
It has shape and functional asymmetry
It gives directionality
Key for migration,development and organization
What is a way to see the structure of cell junctions in a cell
How does it work
Electron microscopy
It uses electrons instead of light
Gives high resultion of the structures
What is special about electron microscopy
The samples are imaged in a vacuum meaning live cells can’t be imaged
What are the three junctions that make up the junctional complex
Tight (zonula occluden)
Adherens
Desmosome (macula adherens)
What are tight junctions
Junctions that tightly hold together neighbouring epithelial cells
At the apical membrane (top of the epithelial cells)
They stop solutes from distributing between each cell
What two functions do tight junction control
The gate function
The fence function
What is the gate function
What is it also called
It’s the function between cells plasma membranes
Where it controls the passage of molecules between cell plasma membranes
The para cellular pathway
What molecules does the gate function control
Ions
Protiens
The blood brain barrier (where ions/water can’t pass but immune system cells can)
Water
What is a tight junction protien that can be mutated and what is the result
Claudin 1
If mutated the cells aren’t tightly close enough so water molecules escape out of the cells
This leads to dehydration
What is the fence function of tight junctions
Occurs in one cell not between cells
But it needs two cells to operate
controls the diffusion of integral membrane protiens between the apical and the basal lateral membranes of the cell
Prevents diffusion and helps create polarity
What does a fence funtion to a tight junctions need in order to actually work
Needs to connect to the actin cytoskeleton and microtubules
In general what can tight junctions interact with
Actin and microtubules
What effect does polarity in tight junctions have on the process of wound healing
The tight junctions are broken due to the paper cut
Since the tight junctions are gone, the apical membrane protiens can move to the basal lateral membrane and vise versa
This cause a loss of polarity in the cell, and a ligand receptor interaction happens which trigger healing
What are the adherins junctions
They connect the external environment around the cell to the actin cyctoskeletion on they inside of the cell
The allow for signals from the external environment to be transmitted to the cytoplasm and nucleus of the cell
What do adherins junctions form around the cell
They form a belt called the zonula adheren which surround the cells apical surface
What are adherins junctions generally made of and what do they depend on
Made of E cadherin
Cadherins are calcium dependent (need calcium to function)
What are desmosomes
They also have cadherins (ca dependent) and are protien rich
the cadherins interact with these protiens to make cytoplasmic plaques on the inside surface of the cells plasma membranes
Then the two cells are anchored together by intermediate filaments (not actin)
What do desmosomes help with
They give strength to a sheet of cells
What are keratin intermediate filaments
They are in epithelial cells and give strength to the cell and tissues
The do this by making a heterodimer made of two diff keratins
These heterodimers make long dense cables
What happens if there is a mutation in keratin genes
What causes the change In keratin gene expression and heterodimers
Skin fragility
Specializations (differentiation)
Where are the most highly specialized cells in a epithelial cell
What about least
At the top (apical end) they lose their nuclei so the cant divide any more
Least is at the bottom which have the most capacity for proliferation and differentiation
