Cell Junctions and Surface Specializations Flashcards
Two classes of cell adhesion molecules
Calcium dependent; calcium independent
Calcium dependent adhesion molecules
Cadherins, selectins
Calcium independent adhesion molecules
integrins, immunoglobulin superfamily
Function of cadherins
Maintain cell-cell contacts. Primarily homophilic adhesions (binds to other cadherins)
How does calcium removal affect cadherins?
Calcium removal stops adhesion and makes cadherins vulnerable to proteases
Adhesion using cadherins is stabilized by
actin cytoskeleton (binding to actin via catenins)
What is the loss of E-cadh erin associated with?
Tumor metastasis
E-cadherin is found in
epithelia
N-cadherin is found in
neural cells
Selectins
Bind to carbohydrates-each selection has carbohydrate recognition domain (CRD). Important for controlling movement of leukocytes from blood into tissues.
P-selectin
platelets, activated endothelial cells
E-selectin
activated endothelial cells
L-selectin
leukocytes (homing receptor)
In selectins, calcium bound at the sides of the CRD regulates
the conformation of the domain and its ability to bind carbohydrates
Outside the cell, the binding site on integrin is on what subunit?
β subunit (binds laminin, fibronectin, tenascin, vitronectin, collagen…)
Inside cell (Integrin) binds to cytoskeletal actin
via actin binding proteins (talin, vinculin, α-actinin)
Adhesion of integrins is stabilized (and destabilized) by
actin cytoskeleton
Immunoglobulin Superfamily
share Ig-like domain;
HIV-1 receptor(CD4 on lymphocyte) is a member of what family
Immunoglobulin Superfamily
Occluding (tight) junctions
prevent free passage across an epithelial layer
In occluding junctions, transmembrane occludin interacts with…
claudin
Why are tight (occluding) junctions medically important ?
Tight junctions are medically important because it can prevent the delivery of drugs to the bloodstream or tissues
Tight junctions determine
epithelial polarity
Cell junction which has a “belt-like distribution”
Zonula Adherens
Zonula Adherens involves interaction primarily with
cadherins and catenins
Desmosomes are stabilized by
intermediate filaments(keratin or vimentin)
Desmosomes lack
afadin-nectin and catenin complexes
Intercellular “rivets”-spot like junction
desmosomes
Hemidesmosomes
anchor basal portion of cell to basal lamina
What is the only asymmetrical junction
Hemidesmosomes
Anchoring filaments involved in Hemidesmosomes
Laminin 5
Communicating junction between cells
Gap junctions
Six integral membrane proteins called connexins associate to form a
connexon
Gap junctions link cells ________ and _________
chemically and electrically
Connexin 26 mutation
deafness
Connexin 32 mutation
Charcot-Marie-Tooth neuropathies: progressive peripheral nerve degeneration
Connexin 50 mutation
congenital cataracts and blindness
Microvilli increase _____ ____ for _________
surface area; absorption
Structure of cilia and flagella
9+2 array of highly stable microtubules
Cilia
hairlike appendages that move fluid-develop from basal bodies (derived from centrioles)
Flagella
propeller for sperm motility (Dyneins provide force for movement)
Kartagener’s syndrome
Loss of dynein = ciliary dyskinesia. Poor respiratory clearance and reproductive sterility
long branching projections that have an actin core(no microtubules or basal body)
non-motile stereocilia
What has the same substructure of microvilli?
Stereocillia
