18 – cells in their environment I: Adhesion & the Matrix Flashcards
Cells interactions
Cells interact & receive signals from their environment:
-Physical connections
–How cells build & regulate
-Chemicals signals
2 types of Cell adhesion (physical interactions) & the cells involved
Cells stick to each other & to their surroundings
Cell-cell adhesions
-CAM – cell adhesion molecule
Cell-matrix adhesions
-Adhesion receptors & CAMs
Cells care about.. & want to
who they stick to
and want to stick to different partners
cells are expressing all of these different types of cell adhesion molecules tells us that cells must want to be able to stick to different types of partners and that they’ll express a particular type of cell adhesion molecule in order to enable them to stick to one type of neighbor and not then to another.
Cell-matrix adhesions
Cell adhesion molecules - CAM
Cells express wide/diverse range of CAMs
Cell-Cell adhesion, molecule involved
-Cadherins: E-cadherins
sticking out into the extracellular space as a series of globular domains.
touching one another across the gap between two cells.
Cell-Matrix, molecule involved
-Integrins (MANY different)
= alpha chain+ beta chain: these are binding to a part of the extracellular matrix, specifically a molecule called fibronectin.
how do cells actually build cell contacts or how is it that they build a way in which they can bind to the extracellular matrix? hwo do cells tick to one another?
-Cis + trans interactions (Velcro)
Cluster large # of CAM adjacent to one another into a patch (Velcro patch)
Cell on opposite side clusters its molecule into a patch of right size & stick together
Cell-cell adhesion =
…strengthened by adding up many weak interactions
…sort out cells of different types into clusters
-Allows cells to sort into clusters in which certain cells will only stick to ones that they like
sponge experiment conclusion:
as much as these cells like to stick to each other, there’s something about the molecules exposed on the extracellular face that is specific and that allows an orange sponge to know that it is stuck to another orange sponge, and a yellow sponge cell to know that it is stuck to another yellow sponge cell.
Something about the molecular outside is specific.
They’re not universally sticky.
They only stick to the things that are like them.
Cadherins can recognize…. & confer…
molecular fingerprint of adjacent cadherin
-Confer molecular specificity
Cell-cell adhesion molecules = Cadherins = …dependent
calcium-dependent molecules
-E-cadherins stick to N-cadherins
Cadherin transgene = cells forced to express E-cadherins
how did they find out cadherins are calcium-dependent molecules?
if you take cells and you express
a coherent trans gene (cells forced to express an E cadherin)
culture them in solutions with calcium, they will cluster together and clump.
But if you remove the calcium, they will not.
Cells express on their extracellular surface:
o Identity
o Preferred binding partners
Cadherins connect to … via…
Cadherins connect to cytoskeleton via adapter proteins
Layers of adapter proteins connect to inner face of cadherins & connect to actin
ECM =
diverse/cross-linked meshwork of polymers
Surround all our cells & tissues
ECM made from
Type IV collagen
Laminin
Entactin/perlecan
Laminins
Laminin = multi-adhesive ECM protein (anchor)
Laminins (Self-assembly) – integrins
-can bind to another laminin
Laminins (Self-assembly)
-can bind to another laminin & collagen
LG domain – bind all sorts of things liekcellular receptors
how does laminin forms the ECM?
take thisthis anchor shaped structure and you start cross linking it together.
And soon enough you have this big cross-linked mesh work of proteins that forms then the extracellular matrix.
Collagen IV networks made of what kind of domains & what type of structure?
heterogenous polymers
-Triple helical
-N-terminal globular domain
-C-terminal globular domain
how is Collagen IV network formed?
collagen for monomer: made of three polypeptide chains.
3 C terminal globular domains wound together bya triple helical structure + N-terminal globular domain can stick to each other in a tetrameric confirmation (4 of the N-terminal globular domains have stuck together with their little triple helices sticking out), globular domains can themselves dimerize = cross link network of collagen IV
Collagen has ….. structure
has triple helix structure (ropes)
Single collagen polypeptide triple helix = form triple helices ( 9 polypeptide chain)
25% of protein mass of human body = Collagen
Collagens connect
tissues together
Main challenge when producing ECMs
How to make these complex protein polymers inside your cells & get it outside of your cells without turning the inside into their outsides?
solution to Main challenge when producing ECMs
By preventing polymerization of collagen fibers inside their ER
