Week 11 - Interactions Between Cells and Their Environment (Junctions and Adhesion) Flashcards
Cells interact with each other in the ECM to form what?
To form tissues.
What are the 4 major ways of cell interaction?
- Anchoring junctions
- Occluding junctions
- Channel-forming junctions
- Signal-relaying junctions
Which 3 junctions are present in epithelial cells?
Anchoring, occluding, and channel-forming junctions.
In polarized epithelial cells, how are junctions arranged?
They are arranged in a specific order.
What is a polarized epithelial cell?
It is a mature epithelial cell.
On epithelial cells, what sides are junctions usually on?
They can be on the basal or lateral side; but most are on the lateral side, discussed as “relatively” apical/basal for visualization and location descriptions.
What kind of junction is a Tight junction?
An occluding-junction.
What do tight junctions do?
They block anything from going between the cells and keep proteins on their correct sides.
Where are tight junctions relatively located on epithelial cells?
They are the apical-most junction; not in one single spot, but all along the region between 2 cells.
What do tight junctions all along the region between 2 cells form?
Form a “sealing strand”, a.k.a. Tight Junction Belt.
What kind of junction is an Adherens junction?
An anchoring junction.
What do Adherens junctions do?
They anchor 2 cells together.
Where are Adherens junctions relatively located on epithelial cells?
They are more basal than Tight junctions; all along the region between 2 cells.
What do Adherens junctions all along the region between 2 cells form?
Form an “Adhesion Belt”.
What kind of junction is a Desmosome?
An anchoring junction.
What do desmosomes do?
They anchor a cell at a PARTICULAR spot.
Where are Desmosomes relatively located on epithelial cells?
They are more basal than Adherens junctions.
What kind of junction is a Gap junction?
A channel forming junction.
What do Gap junctions do?
They form and act as channels.
Where are Gap junctions relatively located on epithelial cells?
Gap junctions are the basal-most junction.
What kind of junction is a hemi-desmosome?
An anchoring junction.
What do hemi-desmosomes do?
They anchor a cell to the Extracellular Matrix (ECM).
Where are hemi-desmosomes relatively located on epithelial cells?
They are ON the basal face; a half-circle kind of shape.
The tight seal created by tight junctions prevent mixing of what 2 things?
- Extracellular environments
2. Membrane proteins
What 2 proteins for the tight seal of Tight junctions?
- Claudin
2. Occludin
Claudin/Occludin are required for what?
For tight junction seals.
The extracellular domains of transmembrane proteins interact with what?
Interact with the extracellular domains of neighbouring cell’s proteins.
Proteins forming tight junction seals interact in what style?
Homotypic style reaction: Occludin with occludin, claudin with claudin.
Tight junctions are dependant on what other kind of junction?
Dependant on Adherens junctions.
If you block the formation of adherens junctions, what happens to tight junctions?
Tight junctions do not form properly.
What 3 junctions for the Junctional Complex of epithelial cells?
- Tight junctions (TJ)
- Adherens junctions (AJ)
- Desmosomes (D)
Occluding-junctions can provide a bit of mechanical strength, but not as much as which other kind of junction?
Not as much mechanical strength as anchoring junctions.
What are 3 examples of anchoring junctions?
- Adherens junctions
- Demsosomes
- Hemidesmosomes
What links cytoskeletal filaments on neighbouring cells?
- adhesion proteins
- transmembrane proteins
- anchor proteins
Intracellular domains of adhesion proteins interact with what?
Interact with anchor proteins.
Extracellular domains of adhesion proteins interact with what?
Interact with neighbouring adhesion proteins and the extracellular matrix.
What do anchor proteins link?
They link adhesion proteins to cytoskeletal filaments via cytosolic proteins.
What does the adhesion belt encircle?
It encirclrs the inside of the plasma membrane.
What 2 “proteins” work at Adherens junctions?
- Cadherin proteins
2. Actin
What do Cadherin junctions do at Adherens junctions?
They are transmembrane proteins that help neighbouring cells interact with each other.
What does Actin do at Adherens junctions?
Actin is tethers to cadherin by anchor proteins.
Why do cells sort themselves into layers? (2 reasons)
- Different cadherin proteins are expressed in each cell type
- Cadherins form homotypic junctions
What do desmosomes and hemidesmosomes link?
Link intermediate filaments, which provide the most structural strength.
Where do hemidesmosomes link filaments?
The link is to the basal lamina, or other parts of the ECM.
What are the 2 adhesion proteins that form Desmosomes?
- Desmoglein
2. Desmocollin
What 2 anchor proteins link the adhesion proteins to intermediate filaments?
- Plakoglobin
2. Desmoplakin
What are Gap junctions composed of?
Composed of connexin proteins; making connexon.
What does a connexon consist of?
6 connexin proteins.
In what 2 ways do gap junctions couple cells?
- Electrically
2. Metabollically
What 4 molecules WILL pass through a gap junction?
- cAMP
- nucleotides
- glucose
- amino acids
What 3 things will NOT pass through gap junctions?
- macromolecules
- proteins
- nucleic acids
One connexon (hemichannel) on it’s own is usually what?
Usually closed.
A dramatic increase in cytosolic Ca2+ will do what to gap junctions?
It will close gap junctions.
Cytosolic Ca2+ is usually what?
Usually low in concentration.
What happens at gap junctions when there is membrane damage?
- Ca2+ leaks into the cell and concentration is abnormally high
- metabolites leak out
If gap junctions remain open, and one cell gets damaged, what happens to the connected cell?
It also gets damaged.
What 2 things is the plant cell wall composed of?
- Cellulose
2. Pectin
What is plasmodesmata?
Plasmodesmata are junctions between plant cells.
How are 2 plant cells connected by the plant cell wall?
- plasma membrane is shared; they share phospholipids, transmembrane proteins, etc.
- they exchange extracellular fluid
- ER extends and forms into other cell’s ER; share organelles
What is the basement membrane of epithelial cells?
Underneath epithelial cells; basal lamina.
What is underneath the basal lamina of epithelial tissue?
Connective tissue.
Connective tissue vs. Epithelial tissue.
Connective: - cells rarely connected - plentiful ECM - ECM provides resistance to mechanical stress - cells attatched to the matrix Epithelial: - cells closely associated - limited ECM - cytoskeletal filaments provide resistance to mechanical stress - cells attatched to eachother
What makes up the Extracellular Matrix (ECM) and some functions?
- connective tissues (composed of fibrous proteins)
- different compositions give tissues different protperties
- ECM remodeled over time