REINHART 3

Question 1

in which situation would gap junctions be closed?

Answer 1

during apoptosis
so that the dying cell’s stuff doesnt go to other healthy cells

Question 2

in which conditions does the closing of gap junctions happen?

Answer 2

high calcium concentrations

Question 3

what are the relative concentrations of calcium in the inside/extracellular cell space?

Answer 3

extracellular: high calcium concentration
inside: low concentration
needs to be tightly regulated

Question 4

how many channels make up big gap junctions?

Answer 4

1000 channels

Question 5

how many channels make up a small gap junction

Answer 5

40-50 junctions

Question 6

what are characteristics of cell adhesions?

Answer 6

visualised with functional assays
transient anchorage
cell to cell recognition
typically before cell junctions are established (early in development)
partially overlapping molecules (cadherins, integrins)

Question 7

what do cell adhesion molecules do?

Answer 7

mediate cell to cell recognition

Question 8

how do neural tube epithelial cells differentiate?

Answer 8

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

Question 9

what will dissociate cells?

Answer 9

trypsin (protease) and EDTA

Question 10

what does EDTA do?

Answer 10

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

Question 11

what value of dissociation constant does EDTA have?

Answer 11

1*10^10M
very high affinity

Question 12

what will happen when you mix two different types of cells together?

Answer 12

the cells of the same will find each other because their CAMs fit together

Question 13

what happens when you mix two cells that have different types of cadherins/different concentration of cadherins?

Answer 13

like goes to like
organise themselves together
find cells that are similar to each other

Question 14

what is special about L cells (fibroblasts)?

Answer 14

do not express cadherins

Question 15

what are the different cell adhesion mechanisms and how often do they occur?

Answer 15

homophilic binding
most frequently, preferred
heterophilic binding
preffered
binding through an extra cellular linker molecule
occasionally possible

Question 16

what are examples of homophilic interactions?

Answer 16

cadherins, bind calciums
Ig-superfamily CAMs
do not bind calciums

Question 17

what are examples of heterophilic interactions?

Answer 17

mucin like CAMs
integrins
both bind calciums

Question 18

what are the different types of cadherins?

Answer 18

1. classical cadherin (E)=TM and cadherin domain
2. fat like cadherins, much larger
3. seven pass TM cadherins (flamingo), combine with G protein receptor
4. protein kinase cadherins (Ret), have signalling functions
5. desmosomal cadherins
6. cadherin 23
7. protocadherins, involved in the central nervous system
8. T-cadherin, doesnt have a TM domain but is anchored to the membrane with a GPI anchor

cadherin domain is always outside the cell

Question 19

how are cadherin domains organised?

Answer 19

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

Question 20

how can cadherins be visualised?

Answer 20

X ray crystallography
NMR spectroscropy

Question 21

what happens when you remove calcium?

Answer 21

cadherins become floppy
cannot interact
leads to degradation by proteases

Question 22

what is avidity?

Answer 22

accumulated strength of multiple affinities

Question 23

what are the relative affinity and avidity levels for cadherins?

Answer 23

low affinity
high avidity

Question 24

through which regions do cadherins interact?

Answer 24

only interact with their terminal domains
there is a flexible hinge region and an N terminal cadherin repeat
perfectly fits, lock and key situation

Question 25

what is the length of the gap between two cells that are bound by cadherins?

Answer 25

38.5nm
rather large gap

Question 26

at what stage of embryonic development do cadherins appear?

Answer 26

at around the 16 cell stage
becomes very difficult to separate the cells now

Question 27

how do protocadherins work?

Answer 27

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

Question 28

how are cells pushed together to make cell-cell adhesions?

Answer 28

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