Cell junctions Flashcards
What are 3 types of cell junctions?
- tight junctions
- cell-cell anchoring junctions
- cell-matrix anchoring junctions (holding hands junction)
What are belt desmosomes?
Cluster of junctions, which are connected to the cytoskeleton. This forms a belt around the cell.
What are cadherins?
transmembrane receptor
What molecule are cadherins dependent on?
calcium
What type of homophilic interactions can be seen in E. cadherin?
E. cadherins bind E. cadherins
How are cadherins anchored together - how do they make strong links between cells?
Homophilic interactions & links to actin cytoskeleton
What are the 2 types of actin-linked junctions?
- Adherens junction (bind to a cell)
- Focal adhesion (bind to extracellular matrix)
Explain the different steps in the adhesion belt in morphogenesis
Cadherin –> Catenin –> Actin –> Myosin
Describe the formation of a neural tube
The sheet of epithelial cells will bend (curve), where contaction occurs, as the basal lamina isn’t very flexible. This leads to invagination and eventually forming a neural tube.
What is the intermediate filament of an integrin?
hemidesmosome
What are hemidesmosomes?
Integrin’s intermediate filament, which attach cells to basal lamina.
What is the intermediate filament of a cadherin?
desmosome
What are desmosomes?
- cell-to-cell junctions
- plentiful in heart muscle & epidermis
What filaments prevent tearing, as long formations across the cell?
Keratin filaments
What is the role of pemphigus?
Contains desmoglein, hold together keratinocytes in epidermis. can cause autoimmune skin blistering.
Between what layers do a tight junction form?
Form between the apical & basal layers of the cells.
What is the function of tight junctions?
- can completely prevent things entering cells. It stops dehydration and regulate what enters. This will present in places where a barrier is needed.
- prevent fluid, ion & membrane flow
(transcellular transport & paracellular transport)
Where are tight junctions found?
epithelial cells - e.g. gut
What are the 2 types of proteins found in tight junction?
occludin & claudin
Approximately how many types of claudin are there?
25 types
What is the result of having different types of claudin?
creates specificity for different tight junction
What 2 protein/lipids can be found on the apical outer membrane?
- glycolipid
- cholesterol
What protein/lipid is found on the basolateral membrane?
- phosphatidylcholine
Where are gap junctions found?
- connective tissue, epithelia, neurons, heart muscle
What can fit through the pores created at gap junctions?
Water, inorganic ions, sugars, amino acid, ATP, cAMP, IP3
What does gap junction regulate?
allows regulated & direct cell-cell communication
What subunits are gap junctions composed of?
6 connexins
What do different compositions of different types of connexins allow for?
this allows for specificity
What regulates gap junctions?
- membrane potential
- pH
- calcium
- cell signals
An influx of what molecule leaking into a neurone will kill a neurone?
Calcium
The addition of what neurotransmitter can lead to gap junctions closing?
dopamine
What are the key uses of junctions?
- Integrity
- Cytoskeleton
- Compartments
- Communication
- Protein families
What are selectins?
surface receptors that bind to sugars
