Lecture 9 Flashcards
What are the four connections/attachments that make the epithelia a barrier?
tight junction
adhering junction
desmosome
gap junction
The epithelia is attached to a _________ _________. Describe this
basement membrane
this is part of the extracellular matrix that holds the cells in place
Describe the cell membrane
It is a lipid bilayer
What is the cell membrane permeable to?
non-polar, uncharged molecules such as O2, CO2 and steroid hormones
What is the cell membrane impermeable to?
ions and large, charged molecules
What are the three things that make up the lipid bilayer? What percentage of the membrane do each of these things make up?
- phospholipids: 75%
- cholesterol: 20%
- glycolipids: 5%
Phospholipids have both a __________ region and a __________ region
hydrophilic
hydrophobic
What two things make up the hydrophilic region of phospholipids?
an alcohol and a phosphate
Where are the hydrophilic and hydrophobic regions of the phospholipids located?
The hydrophilic regions face the outside and inside of the cell and then the hydrophobic region faced each other, away from the aqueous inside and outside of the cell
Is the hydrophilic head on cholesterol big or small? Why is this?
it is small so that it can be embedded in the lipid region
There are ________ in the membrane which span the whole lipid bilayer. What are three examples?
proteins
GPI-anchored membrane protein
peripheral membrane protein
integral membrane protein
Which protein does not span the membrane but holds onto it?
the peripheral membrane protein
What is meant by the fluid mosaic of the lipid bilayer?
lipid molecules can move sideways in their own half of the bilayer
Can proteins such as channels, receptors, transporters, ECM proteins move in the bilayer?
yes
they are embedded in the lipid bilayer but can still move
What is the purpose of the fluid mosaic of the lipid bilayer?
it is __________ and __________ for changing _________ and _________ populations, cell _______, _________ and self-sealing
it is flexible and dynamic for changing protein and lipid populations, cell growth, secretion and self-sealing
What is another name for the basement membrane?
basal lamina
What joins the cells to the basement membrane?
hemidesmosomes
Where are tight junctions located?
these are located close to the apical membrane of the cells
Where do adhering junctions sit?
just below the tight junctions
What is the basement membrane? What is it comprised of?
it is an extracellular matrix structure comprised of collagens, laminins, proteoglycans and fibronectins
Where is the basement membrane secreted from?
from the epithelial cells themselves to help form the extra cellular matrix structure that they then sit on
What is a condition that results from issues with the basement membrane?
epidermolysis bullosa
What causes epidermolysis bullosa?
the collagen malfunctions so the anchoring of the basement membrane to the skin epithelia 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
A- Both true and related
What are the three main functions of the tight junctions?
- act as a barrier
- act as a gate
- act as a fence
Explain the tight junctions acting as a barrier (why is this needed?)
this limits the passage of ions and molecules between cells in the paracellular pathway
Explain tight junctions acting as a gate (why is this needed?)
it can allow certain solutes to flow through the paracellular pathway
Explain tight junctions acting as a fence (why is this needed?)
to prevent the movement of proteins between apical and basolateral domains
Tight junctions are ________ structures around each epithelial cell - formed by strands of _______ proteins linked to bilayers of two cells pulling the bilayers very close together
continuous
claudin
What three things make up a tight junction?
- claudin protein
- occludin protein
- JAMs
What are claudin proteins, occludin protein, JAMs all connected to?
ZO proteins
What are ZO protein connected to?
actin cytoskeleton
What is the part of the tight junction that changes to make all 27 different kinds?
the claudin
What does claudin 1 not allow through the tight junctions?
it does not allow transport of ions/water through the tight junctions
What does claudin 2 allow through the tight junctions?
it allows the transport of many ions and water through the tight junctions
Other claudins (not 1 or 2) control the passage of what?
Mg2+, Ca2+
Describe the structure of the adherens junction
this is a belt structure beneath tight junction where two cells are close contact via cell-cell adhesion molecules (CAMs)
What makes up the belt that forms part of the adherens junction?
actin filaments
Formation of adherens junction initiates epithelia formation, true or false?
true
What is an example of a CAM?
E - cadherin
CAMs are held in place by what?
by anchor proteins which connect to actin cytoskeleton
Why are CAMs important in cancer?
As the cancer progresses, the epithelia becomes mesenchymal and can cause metastasis due to the loss of adherence junctions so the epithelia become disorganised so the cells break off and go somewhere
Describe the structure of desmosomes
There are desmosomal cadherins that hold cells together at single spots. There is an anchor point for intermediate filaments eg. keratin
Describe the structure of a hemidesmosome
These connect the epithelial cells to the basement membrane and are directly involved with keratin intermediate filaments (these are embedded in a plaque and joined via the protein plectin to integrins)
Describe gap junctions
These are tiny channels between cells made of connexin proteins
Six connexins form a ________ that forms a _________
connexon
channel
What do gap junctions allow the passage of?
ions and small molecules between cells
What are the three main types of cytoskeleton?
- actin filaments
- intermediate filaments
- microtubules
What is the purpose of actin filaments in the cytoskeleton?
determines cell shape, and drive the movement of cells
What is the purpose of the intermediate filaments in the cytoskeleton?
to provide mechanical strength and resistance to shear stress
What is the purpose of microtubules in the cytoskeleton?
to position ___________, railroads for intracellular ________ transport, form a _________ spindle, motile components of _________
to position organelles, railroads for intracellular vesicle transport, form a mitotic spindle, motile components of cilia
The cytoskeleton is ________ and can ________ to internal and external signals
dynamic
adapt
____________ proteins regulate the _______/_________ and linking to other structures
accessory
assembly/disassembly
Actin filaments form a ______ stranded _______ polymer of actin
2
helical
What are myosins?
they are ________ proteins that bind to ________ filaments and use _______ for ________, and transport _______, vesicles and ________ along the _________ filaments
they are motor proteins that bind to actin filaments and use ATP for contraction, and transport proteins, vesicles and organelles along the actin filaments
What are microtubules?
they are long straight hollow cylinders made from α and β tubulins
Which is more rigid, actin filaments or microtubules?
microtubules
What are microtubules needed for?
cell motility, cell division, vesicle movement
What are two molecular motor that allow transport of vesicles and organelles around the cell using ATP?
kinesin and dynein
What type of cell junction is a tight junction: occluding Anchoring strength communicating
occluding
What type of cell junction are adherens: occluding Anchoring strength communicating
anchoring
What type of cell junction are desmosomes: occluding Anchoring strength communicating
strength
What type of cell junction are hemidesmosomes: occluding Anchoring strength communicating
strength
What type of cell junction is a gap junction: occluding Anchoring strength communicating
communicating
What are the transmembrane proteins for tight junctions?
claudin, occludin, JAM-1
What are the transmembrane proteins for adherens?
E - cadherins
What are the transmembrane proteins for desmosomes?
desmosomal cadherins
What are the transmembrane proteins for gap junctions?
connexins
What is the cytoskeletal attachment for adherens?
actin filaments
What is the cytoskeletal attachment for desmosomes?
keratin filaments
What is the cytoskeletal attachment for hemidesmosomes?
keratin filaments
Desmosomes connect epithelial cells to the basement membrane BECAUSE the basement membrane consists of extracellular matrix proteins
False, true
