2.3: Cell Adhesion Flashcards
cell __________ and __________ is essential for multicelllular organisms
polarization, cohesion
polarized cells can? (3)
- define inside vs outside
- have diff functions at diff cell regions
- transmit signals
how is mechanical stress transmitted from cell to cell in epithelial tissues
by cytoskeletal filaments anchored to cell-matrix and cell-cell adhesion sites
the extracellular matrix directly bears what type of stress (and 2 types of this specific stress)
mechanism: tension and compression
what is connective tissue made up of
collagen fibers, ecm, cells kinda spaced far apart
many animal cells are either connective or epithelial tissue, what are these?
epithelial tissue: cells directly connected to each other w minimal ecm (basal lamina sometimes considered part of epithelial tissue)
connective tissue: cells dispersed through ecm
state what epithelial cells line and provide examples
surfaces: protective epithelial cell layers on the surface of the organism (skin)
cavities: absorptive epithelial cells lining a cavity of the organism (digestive tract)
organs: epithelial cells surrounding and defining organs
t/f are lining patterns consistent
true
t/f are epithelial cells polarized and explain how
true. each cell surface must be different to perform different functions, these cell surfaces define the inside vs outside of the organism or tissue
list the junctional complexes of (mature) epithelial tissues from apical to basal
tight junction, cell-cell anchoring junction, channel forming junction, cell-matrix anchoring junctions
define tight junctions
seals gap between epithelial seals. all along the region between two cells, makes sealing strands
the order of junctional complexes from apical to basal are distinct, are these the same in all cells
- mature cells definitely have junctions and in that order
- other cells may or may not have all of them or in that order (case to case dependent)
what makes sealing strands and what makes adhesion belts
tight junctions make sealing strands and adherens junctions make adhesion belts
define adherens junction
connects actin filament bundle (apart of cytoskeletal filaments) in one cell with that in the next cell. the actin anchors on that side of the cell and doesn’t go to other side, the adherens junction is all along region between two cells to form adhesion belts
define desmosome
desmosomes connects intermediate filaments (cytoskeletal filaments) in one cell to those in the next. desmosomes are just in that spot and don’t go to the other side.
define gap junctions
allows the passage of small water-soluble molecules from cell to cell (not with outside cell)
what does relative positioning mean in epithelial cells
it’s when there is greater presence of a junctional complex on the apical vs basal side - eg desmosomes more apical than gap junctions
what (2) types of junctional complexes connect the epithelial cell of the basal connective tissue underneath
- actin linked cell matrix junction: anchors actin filaments in cell to ecm
- hemidesmosome anchors intermediate filmaments in cell to ecm
note that filaments don’t go outside (cytoSKELETAL stays inside)
which junctional complexes are considered cell cell junctions
adherens and desmosomes
which junctional complexes are considered cell-ecm junctions
actin linked cell matrix junction and hemidesmosomes
cell cell junctions are usually mediated by ____________ and cell-ecm junctions usually mediated by ___________ and cytoskeleton may be _______ or ____________ filaments
cadherins. integrins, actin or intermediate filaments
*cadherins is for adherin junctions and cadherin family is for desmosomes
what are intracellular adaptor proteins used for
they are inside the cell and they hold the transmembrane adhesion proteins while the other end of the tm prot either is cell-cell or cell-ecm
cadherins are tm proteins expressed by (one or both) cells - cadherins mediate cell-cell connections at adherens junctions
both (it’s like velcro)
cadherins interact (homophilic or heterophilic) interactions of their extracellular domains
homophilic - N terms of both connect
ie e cadherin can go w e cadherin but cannot go with n cadherin
cadherins interactions require what and what does it do
ca2+ - makes hinge regions rigid to help them stick together (think of wrists as the hinge in regards to arm)
what is the result of homophilic cadherin interactions
cells expressing different cadherins sort into two separate groups that do not interact
cadherins form homophilic interactions with their ec domains to directly link _____________ and indirectly interact with __________-_
adjacent cells, actin filaments
do cahrerins act directly or indirectly with actin filaments, and what is the result
indirectly ==> these interactions indirectly link the actin cytoskeleton between adjacent cells in epithelial tissues
caherins interact in patches to form a strong _________ belt
adhesion
adhesion belts can mediate ?
morphogensis
describe morphogenesis by adhesion belts
the sheet of epithelial cells can undergo invagination caused by an organized tightening of adhesion belts in selected regions of the cell sheets (the actin contracts = tightening = shape forming) -> epithelial tube pinches off from overlying sheets of cells -> then it can become a shape eg the epithelial tube
t/f you need the correct cadherins to create specific shapes through morphogenesis
true
in an ectoderm, cells express different cadherins to establish new interactions and ensure the closure of which feature
neural tube closure (the neuron tube is joined by a different cadherin that made up the original ectoderm and the original cadherin that makes up the neural tube)
cell adhesion is essential for which 2 processes
embryo development (must adhere properly so when the cells move itll be coordinated movements to separate head from a foot yk) and morphogenesis
Which of the following most closely resembles adherens junctions
mutations in the outer epithelium of Drosophila embryos?
a) Hemidesmosome mutation in the outer epithelium.
b) Calcium removal at the outer epithelium.
c) Intermediate filament depolymerization in the outer epithelium.
d) Occludin mutation in the outer epithelium.
B.
A is wrong bc if doesn’t resemble. B is right be we need calcium to make it rigid so no calcium will make it flimsy thus the embryo won’t develop properly. C is wrong bc it’s not intermediate filaments, I think it’s actin (double check). D is wrong bc occludin is for tight junctions.
tight junction define the _____ of the cell
domains - they separate apical and basal
state what the apical and basal domain face
apical - surface, cavity, organ
basal - inside of the body
occludins and claudins form ___________ and these form ________ strands
tight junctions == sealing strands
* many rows of these proteins are needed to form a functional tight junction
claudin and occludin are tight junction proteins with how many passes into the TM
4
occludins and claudins for homo or heterophilic interactions with their ec domains to directly link adjacent cells
homophilic
is linking of adjacent cells by tight junctions direct or indirect
direct
tight junctions limit diffusion into the __________ space and limit the diffusion of what
extracellular, membrane proteins
membrane proteins can or cannot diffuse in the plasma membrane
can
which junctional complex prevent membrane proteins from moving between the apical and the basolateral domains
tight junctions
explain how tight junctions regulate what enters an organism (in the example of absorbance of glucose from the intestinal lumen)
- tight junctions function to stop anything from directly diffusing from the gut lumen into connective tissue and blood
- active transporters (Na+ driven glucose transporter) must move glucose into the epithelial cell on the apical domain from the gut lumen (low C gluc bc keeps being moved into cell)
- passive carriers (passive glucose transporter) in the basolateral domain allow glucose to diffuse out of the epithelial cell into the connective tissue/blood
- tight junctions keep the correct transporters in their correct domains of the cell
in the absorbance of glucose from the intestinal lumen, state the 2 relevant transporters and which domain they are in
na+-driven glucose transporter (active) in the apical
passive glucose transporter (passive) in basolateral
_______________ mediate cell to cell matrix junctions
integrin heterodimers
integrins directly or indirectly interact w actin filaments
indirectly
cell matrix junctions play roles in both epithelial and connective tissues, define these both
epithelial tissue: adhesion to the basal lamina ecm
connective tissue: cell interaction iwth the ecm and cell movement
what are polarity cues
signal to make ends different, these can establish cell cohesion
what is cell cohesion established by
polarity cues
describe how polarity cues can establish cell cohesion and examples
- adherens junctions form first, this is the primary landmark –> subsequent elaboration
- adherens junctions provide polarity cues to define apical from basolateral domains for epithelial cells (the first polarity cue defines the rest)
- tight junctions form apical to the adherens junctions-after the separation of apical and basolateral
example: adherens junction cause the polarity cues of par and crumbs to dictate the apical domain. it inhibits scribble (polarity cue) which creates the basolateral domain
t/f only epithelial cells use the polarity cue systems
no, all cells
state what an initial landmark (can be strucutre, prot, signal, or process) generate
subsequent patterns
describe how ec signals can polarize cell behaviour in regards to rac and rho
on neutrophils, the chemoattractant acts on the receptor which is the primary landmark that indicates rac (polymerization (- protrusion)) to go towards and rho to go away (actin-myosin contraction)
t/f cell polarity can be established external OR internal signals
true
describe how external signal (sperm entry) can establish cell polarity
the initial polarity signal was external (sperm entry) which is the primary landmark. asymmetric cell division can unevenly distribute internal polarity cues between child cells – defining the anterior and posterior through the rho gef gradient.
An occludin mutation in ________ cells will directly affect __________.
a) intestinal epithelial; glucose transport.
b) Drosophila embryonic; movement of the outer epithelium.
c) Drosophila embryonic; segmentation of the outer epithelium.
d) epithelial; adherens junction formation.
A.
B is wrong bc movement is for cadherin. C is wrong bc we don’t even know segmentation. D is wrong bc if adherens it’s a whole separate thing and they form before tight junctions
list the 3 key components of cell polarity to define a functional epithelium
intracellular trafficking, cytoskeleton organization, cell cohesion
what does a functional epithelium define
organs and organisms by separating proteins on sides and keeping them there
