Exam 3 pt 2 Flashcards
epithelial cells rely
on cell-cell junctions
connective tissue cells rely on
cell matrix junctions
tight junctions have _ and function to _
no resistance to stress and prevent leaking
intracellular domains of transmembrane adhesion linked to _ proteins are while extracellular domains are linked to
linked to cytoskeletal filaments, structures outside of the cell
superfamilies of adhesion proteins
- integrins
- cadherins
cadherins for _ via _
cell cell junctions via actin adherens junctions or intermediate filament desmosomes
integrins form _ via
cell matrix junctions (to ECM) via actin linked cell matrix junctions or intermediate filament hemidesmosomes
all cadherin family members
have several copeies of the extracellular adherin domain
in cadherins, adjacent domains are linked by
flexible hinges
classical cadherins have
closely related sequences in their intracellular and extracellular domains
nonclassical cadherins are
are more distantly related in sequence
intracellular domains of cadherin are
more diverse because IC domain interact w many unique things
the _ of cadherins interact in the _
amino termini of cadherins interact in the extracellular space between adjacent cells
how do cadherins bind
- end domains of cadherin contain a knob and pocket
- knob of one cadherin insert into pocket of another
- distance between cells determined by structure of cadherins
cadherin interactions are regulated by
extracellular Ca levels
how are cadherin interactions regulated
binding of Ca to hinge regions prevents EC domains from flexing, resulting in a slightly curved rod
* without Ca, hinges are flexible and the cadherin domains become floppy
* w/o Ca, reduced affinity between cadherins
how are cadherin interactions regulated
binding of Ca to hinge regions prevents EC domains from flexing, resulting in a slightly curved rod
* without Ca, hinges are flexible and the cadherin domains become floppy
* w/o Ca, reduced affinity between cadherins
cadherins bind to each other with
low affinity ( weak bonds)
how do cadherins form a strong junction
clusters of cadherins on one cell bind to clusters of cadherins on another
* accumulation of many weak bonds form velcro effect
cell sorting is mediated by
cadherins
cell sorting is mediated by
cadherins
cell sorting by cadherins explained
cell sorting recognize based on type and level of cadherin expression
* same cadherins stay together, more expression make inner layer called primary ball which has tighter interactions
_ is important for developmet
differential expression of cadherins
switching off of _ can allow cells to dissociate and form migrating cells
E-caderin
mutations that disrupt _ are found in cancer cells
production of E cadherins
in adherens unctions,
the intracellular domains of cadherins are indirectly linked to actin filaments
proteins in between them that link the two
adhesion belt
networks of actin filaments of adjacent cells connected via adherens juctions, located just beneath the apical surface of an epithelium
contraction of adhesion belt
provides the force required to fold epithelial sheets during development
* invagination pinches off to form tubes, vesicles and other structures
desmosomes are
clusters of non classical cadherins forming spot like welds that link intermediate filaments networks of adjacent cells
snaps NOT velcro
desmosomes are
clusters of non classical cadherins forming spot like welds that link intermediate filaments networks of adjacent cells
snaps NOT velcro
plakoglobin and plakophilin are used
cadherins linking to IFs
tight junctions enable _ by
unidirectional transport, by preventing molecules from passing between cells and the movement of transporters between apical and basaolateral domains
tight junctions form seals between
adjacent epithelial cells
in freeze-fracture, tight junctions
appear as branching network of sealing strands encircling the apical membrane
structure of tight junctions
- sealing strans of occludin and claudin proteins extracellular domains adhere and bring the lasma membranes into close proximity
- makes a tight junction
structure of tight junctions
- sealing strans of occludin and claudin proteins extracellular domains adhere and bring the lasma membranes into close proximity
- makes a tight junction
tight junctions are composed of three types of transmembrane proteins
claudin, occludin, tricellulin
claudin
- most abundant isoform
- essential for formation and function of tight junctions
- losds is fatal
occludin is important
- important for limiting the permeability of tight junctions
tricellulin is required
to seal membranes and prevent paracellular leakage at the junction points between three cells
ZO proteins
- bind to the cytoplasmic domains of adhesion proteins
- function as scaffold proteins that provide a structural support on which the tight junction is built
gap junctions form
direct passageways between cells
gap junctions structure
- 6 transmembrane **connexin proteins ** assemble into a hemichannel connexons
- connexons of two adjacent cells align to form an aqueous channel connecting the cytosols of the cells
size of gap junctions vary
with the number of connexons in the cluster pairs that form gap junctions
connexons can be
homomeric or hetromeric
regulation of gap junctions
- switch between open and closed states in response to many things
turnover of gap junctions
- new connexons are added to the periphery of a gap junction
- old connexons are removed from the center
- very rapid turnover rate
- before they are connexon, they are unpairs hemichannels
gap junction role in muscle
electrically couple cardiac and smooth muscle cells so there is no delay and there is synchrony (ex heart beat)
selectins are
cell surface, carbohydrate binding proteins with a conserved lectin domain
selectins are
cell surface, carbohydrate binding proteins with a conserved lectin domain
L selectin are found in
white blood cells
emigration of white blood cells at sites of inflmmation
- cytokines are release
- epithelial cells express E selectin
- rolling: selectin binds to carbohy on leukocytes weakly so that the leukocyte can roll along the vessel wall
- adhesion integrinds bind to ICAMs and the attachement of leuk to epith cell is stronger
- leuk can stop rolling and squeeze through in between epith cells to escape
Tissues are composed of
cells and the ECM
Components of ECM
- Fibers (insoluable): Collogen, Elastic
- Ground Substance (soluable): Glycosaminogllycans, Proteoglycans, Multi domain glycoproteins
Glycosaminoglycans are
unrbanched polysaccharide chains composed ofo a repeating disaccharide units
* very high negative charge, causing sugars to be repealed by each other and spread out and take up a lot of volume
GAGs negative charges…
attract positive ions and water, so they form hydrated gels that resist compression
hyaluronan
a unique GAG that is v large and has no sulfated sugars and is not linked to a protein core
proteoglycans are composed of
GAG chains covalently linked to a core protein
* core protein and GAG chains point out like a bristles of a straw cleaner
proteoglycan synthesis
- core protein is synthesized by membrane bound ribosomes
- in the golgi, linkage tetrasaccharide is attached to a serine side chain on the core protein
- GAG residues are added to the tetrasaccharide one sugar at a time
decorin
proteoglycan that has one GAG, binds to collagen fibrils and regulates their assembly
aggrecan
proteoglycans that has a lot of GAGs, main proteoglycan in cartilage
proteoglycans can regulate
the activities of secreted proteins by binding to the secreted signal molecules and regulating their diffusion through the matrix
cell surface proteoglycans
integral components of the plasma membrain, core protein is inserted across the plasma membrane or attached via a GPI anchor
_ is the most abundant protein in animals
collegen
collegen molecules structure
- made up of three alpha chains wound around one another in a ropelike superhelix
- alpha chains are made up of a series of triplets Gly-x-x
- glycine is small so the alpha chains are closely packed
type one collagen are found in the
skin and bones
collagen fibrils are formed by
collagen molecules aligned head to tail in overlapping rows
collagen fibers are
bundles of collagen fibrils