REINHART 3 Flashcards
in which situation would gap junctions be closed?
during apoptosis
so that the dying cell’s stuff doesnt go to other healthy cells
in which conditions does the closing of gap junctions happen?
high calcium concentrations
what are the relative concentrations of calcium in the inside/extracellular cell space?
extracellular: high calcium concentration
inside: low concentration
needs to be tightly regulated
how many channels make up big gap junctions?
1000 channels
how many channels make up a small gap junction
40-50 junctions
what are characteristics of cell adhesions?
visualised with functional assays
transient anchorage
cell to cell recognition
typically before cell junctions are established (early in development)
partially overlapping molecules (cadherins, integrins)
what do cell adhesion molecules do?
mediate cell to cell recognition
how do neural tube epithelial cells differentiate?
cells that will become neural crest cells crawl out of that space
those cells migrate, crawl along matrix molecules
aggregate
differentiate Ito satellite cells and nerve cells, forming the peripheral ganglia
different cadherins are at different locations
what will dissociate cells?
trypsin (protease) and EDTA
what does EDTA do?
binds metal ions (Ca2+)
chelating compound
when EDTA binds to the calcium ions, which are necessary for cell to cell adhesion, the cells will not bind each other
what value of dissociation constant does EDTA have?
1*10^10M
very high affinity
what will happen when you mix two different types of cells together?
the cells of the same will find each other because their CAMs fit together
what happens when you mix two cells that have different types of cadherins/different concentration of cadherins?
like goes to like
organise themselves together
find cells that are similar to each other
what is special about L cells (fibroblasts)?
do not express cadherins
what are the different cell adhesion mechanisms and how often do they occur?
homophilic binding
most frequently, preferred
heterophilic binding
preffered
binding through an extra cellular linker molecule
occasionally possible
what are examples of homophilic interactions?
cadherins, bind calciums
Ig-superfamily CAMs
do not bind calciums
what are examples of heterophilic interactions?
mucin like CAMs
integrins
both bind calciums
what are the different types of cadherins?
- classical cadherin (E)=TM and cadherin domain
- fat like cadherins, much larger
- seven pass TM cadherins (flamingo), combine with G protein receptor
- protein kinase cadherins (Ret), have signalling functions
- desmosomal cadherins
- cadherin 23
- protocadherins, involved in the central nervous system
- T-cadherin, doesnt have a TM domain but is anchored to the membrane with a GPI anchor
cadherin domain is always outside the cell
how are cadherin domains organised?
between each domain there are calcium binding sites
2, but 3 on the terminal domains
keep the cadherin in rod type conformation
important for the structure
cadherin is made up of beta sheets
how can cadherins be visualised?
X ray crystallography
NMR spectroscropy
what happens when you remove calcium?
cadherins become floppy
cannot interact
leads to degradation by proteases
what is avidity?
accumulated strength of multiple affinities
what are the relative affinity and avidity levels for cadherins?
low affinity
high avidity
through which regions do cadherins interact?
only interact with their terminal domains
there is a flexible hinge region and an N terminal cadherin repeat
perfectly fits, lock and key situation
what is the length of the gap between two cells that are bound by cadherins?
38.5nm
rather large gap
at what stage of embryonic development do cadherins appear?
at around the 16 cell stage
becomes very difficult to separate the cells now
how do protocadherins work?
there is a gene with multiple exons for variable region domains (extracellular domains), separated by introns including promoters, and exons for constant region (intracellular domain)
through transcription and RNA splicing
only the terminal exon is maintained and others are spliced out
each exon is preceded by its own promoter
the constant region is always kept
translation leads to protocadherins
one exon codes for the entire extracellular domain
how are cells pushed together to make cell-cell adhesions?
Rac1 is kept inactive in cytosol by GDI (GDP dissociation inhibitor Rho)
GDI goes away
Rac1 localises to the PM
this activates PI3K (phosphoinositide 3-kinase) which activates GEF (Tiam1) which activates Rac1 (not GTP bound)
this creates a force that pushes on the PM and the two cells push towards each other
actin assembly
