L9 Flashcards
what are the 4 structures that hold epithelial cells together
tight junctions
adhering junctions
jap junctions
desmosomes
what is the role of microvilli
to increase the surface area
what is the role of the basement membrane
it is a supporting cushion for epithelial cells to sit on
what is the composition of the lipid bilayer
75% phospholipids
20% cholesterol
5% glycolipids
there are also very small amounts of other lipids
where does cholesterol sit in the membrane
it doesn’t have a hydrophobic head region therefore it sits deep in the membrane
what is an example of a glycolipid and what is it involved in
GPI is involved in protein trafficking
what are some of the roles that other lipids could have in the membrane
cell signalling and trafficking
what are the 2 different types of proteins in the lipid bilayer
internal membrane proteins and peripheral membrane proteins
describe internal membrane proteins
these span the entire lipid bilayer
eg Na and K channles
describe peripheral membrane proteins
these dont span the entire lipid bilayer. they are found inside the cell attached to internal membrane proteins
are the membranes static
no
what is the mosaic model of the lipid bilayer
Lipid molecules can move
sideways in their own half of the bilayer.
Proteins such as channels,
transporters, receptors, extracellular matrix proteins
etc are embedded in the lipid bilayer, but can also move within the bilayer (eg they can move along it
why is the mosaic model possible
because the bilayer is very flexible and dynamic for changing protein and lipid populations, cell growth, secretion and self sealing
what is the basement membrane
an extracellular matrix structure
what is the order in which you would find joining structures of the epithelial cells going from most apical to basolateral
tight junctions
adhering junction
desosomes
gap junctions
hemidesmosomes
what are some characteristics of the basolateral membrane
it is thin, flexible but tough and prevents cell movement
where are the proteins needed for the basolateral membrane secreted from
epithelial cells
what is epidermolysis bullosa
it is caused by collagen malfunctions so the anchoring of skin epithelial to the basement membrane (through hemidesmosomes) fails and blistering occurs
Patients presenting with epidermolysis bullosa present with severe blistering
BECAUSE
collagen dysfunction prevents proper anchoring of basement membrane to the epithelial cell
both are true and related
what are the 3 main functions of tight junctions
they act as a
barrier
gate
fence
how do tight junctions acts as a barrier
they limit passage of ions and molecules between cells in the parracleeulat pathway (between cells)
how do tight junctions acts as a gate
they allow certain solutes to flow through the paracellular pathway
how do tight junctions acts as a fence
they prevent the movement of proteins between the apical and basolateral domains
what is the importance of tight junctions acting as a fence
it helps to maintain the basal and apical polarity
these membranes need to be different because this is what makes epithelial cells epithelia
and tight junctions continuous or random
tight junctions sit close to the apical membrane and form a continuous structure
how does the continuous tight junction form
it is formed by stands of claudin proteins linked to lipid bilayers to 2 cells pulling them together
what structures are found in tight junctions
JAMs
claudin
occludin
what is the role of JAMs, claudin and occludin
They all connect to proteins called ZO proteins. They then connect to the actin cytoskeleton which is what holds the tight junctions in place
are all tight junctions the same
no
what is the only structure in the tight junction that changes and how many different types are there
claudin and there are 27 types
if a tight junction contains claudin 1 what characteristics will the tight junction have
no transport of ions/water molecules through the paracellular pathway
where would tight junctions containing cludin 1 be located
in the skin and glomerulus
without them in the skin water would just seep out of us therefore we would die without it
what are the characteristics of tight junctions with claudin 2
allows for transport of main ions and water through the paracellular pathway
where would tight junctions containing cludin 2 be located
in the intestinal crypts and the proximal renal tubule
what are the different names for the adherens junctions
zonular adherens
what structure do multiple zonular adherens form
a belt structure just below the tight junctions
what is the adherence belt made up of
what filament
actin filaments. it is the CAMs that being the 2 epithelial cells close together
formation of adherens junctions initiates what
epithelia formation
what is E cadherin
CAM
E stands for epithelial
explain how E cadherin is related to cancer
E cadherin is important with cancers, breast cancer is an epithelial cancer. As it progresses the Ec loos the epithelial characteristics. This new cell is called mesenchymal. Then the epithelial cells becomes mesenchymal they are able to metastasise
The key part that drives this change is the loss of E cadherin causing the loss of formation of these adherence’s junctions causing the epithelial cells to become disorganised. When this is what allows the cells to brake off and get into the blood streem and metastasis
The cadherins bring the cells together and then these are held in place by anchor proteins from the epithelial cell. These proteins are attached to the actin cytoskeleton
describe the characteristics of desmosomes
These hold epithelial cells together in single spots (not continuous)
They brings cells together through desmosomal cadherins
These are the anchor point for intermediate filaments which are part of the cytoskeleton which is made of keratin
where are hemidesmosomes found
joining the basal lamina to epithelial cells
what do hemidesmosomes consist of
they are keratin (intermediate) filaments which are embedded in a plaque and joined via the protein plectin to integrins
what is the role of the integrins (in relation to hemidesmosomes)
Integrins help to integrate the hemidesmosomes to the basal laminar
what are gap junctions
they are tiny channels between cells made of connexin proteins
the permit regulated passage of ions and small molecules
not continuas they are in single spots
what is the difference between a connexin and a connexon
connecOn = a group of six connexIns
how small do molecules need to be to move through gap junctions
< 1000 Da
what forms a channel
between 2 cells
when a conexon on one epithelial cell lines up with a conexon on another epithelial cell
what are the 3 main cytoskeletal types
actin filaments
intermediate filaments
microtubules
what does actin do in the cytoskeleton
it determines cell shape and dives the movement of cells therefore playing a role in cancer migration
what is the role of intermediate filaments
provide mechanical strength and resistance to shear stress (Eg when the wind blows your hair up (when its parallel to your head).
what is the role of microtubules
to position agranells, railroads for intracellular vesicle transport, form the mitotic spindle and is the motile component of cilia
what is an important feature of the cytoskeleton
that it is dynamic and able to adapt to internal and external signals
what is the role of accessory proteins in the cytoskeleton
to regulate the assembly and disassembly of things
they also link other structures together
what do actin filaments consist of
2 stranded helical polymers of actin
what is the role of myosins in actin filaments
they are motor proteins that bind to actin filaments and use ATP for contraction, transport proteins, vesicles and organelles along that actin filaments
what are microtubules made of
alpha and beta tubulins
what are microtubules needed for
cell motility, division and vesical movement
what are kinesin and dynein in relation to microtubules
they are molecular motors that allow transport of vesicles and organelles around the cell using ATP
they are accessory proteins
Desmosomes connect epithelial cells to the basement membrane
BECAUSE
the basement membrane consists of extracellular matrix proteins
the first is false (should be hemidesmosomes) and the second is true
