Extracellular Matrix Flashcards
What are the 2 different forms of direct binding between cells?
Cell-cell junctions
Cell adhesion
What difference type of tissues are found in the intestinal wall?
- Epithelium → sits on basement membrane
- Connective tissue (fibroblasts)
- Smooth muscles: Circular fibers, Longitudinal fibers (crossing each other making leaf)
- Connective tissue
- Epithelium
What are the 3 major classes of cell junctions (and their main function)?
- Occluding junctions → Seal cells together in an epithelium, no leaking from one side to the other
- Anchoring junctions → Mechanically attach cells to the neighbours or to the extracellular matrix
- Communicating junctions → Mediates the passage of signals from one cell to the next
What are the 2 types of occluding junctions?
- tight junction (vertebrates only)
- septate junctions (invertebrates mainly)
What are the different types of anchoring junctions?
Actin filament attachement sites:
- cell-cell junctions (adherens junctions)
- cell-matrix junctions (focal adhesions)
Intermediate filaments attachement sites:
- cell-cell junctions (desmosomes)
- cell-matrix junctions (hemidesmosomes)
What are the 3 types of communicating junctions?
- Gap junctions
- Chemical synapses
- plasmodesmata (plants only)
What organisms/organelles can you see with a light microscope?
Light wavelength ~ 400-700 nm
- Chloroplast (1um)
- Most bacterias (1-10 um)
- Plant/animal cells (10-100 um)
- Fish egg (> 1mm)
What is the range of molecules you can see with an electron microscope?
<1 nm - 100 um
- small molecules (< 1nm)
- lipids (~2-4 nm)
- proteins (5-10 nm)
- T2 phage (70-80 nm)
- Chloroplast (1 um)
- Most bacteria (1-10 um)
- Plant/Animal cells (10-100 um)
*um = micron
How does an eletron microscope work?
From top → bottom:
1. Electron gun (Cathode = e- donor, Anode = acceleration)
2. Condenser lens
3. Specimen
4. Objective lens
5. Projector lens
6. Viewing screen/photographic film
*Ultralow vacuum necessary for electrons to become scattered by collision with air molecules
*Wavelength of an electron decreases as velocity increases → accelerating voltage = 100 000V → 0.004 nm wavelength
What is Osmium tetroxide?
It is an electron dense (atomic number = 76) staining agent for the specimen to get contrast in image of electron microscopy
It binds to lipid bilayer and proteins
*Dark areas = dense materials
How can we use a tracer to visualize tight junctions?
- Inject a tracer molecules in gut lumen
- Follow the molecules → goes in microvilli
- Tracer molecule stops at the tight junction
*Occulins and Claudins bind to hold adjacent plasma membranes together with intercellular spaces between seals
What are the tight-junction proteins formin the sealing strands (and their properties)?
Claudin: (Primary component)
- 20-27 kDa
- 24 homologous members (24 genes)
- Specificity: claudin in kidney epithelia → Claudin-16 required for Mg2+ to be reabsorbed from the urine into the blood → mutation causes excessive loss of Mg2+ in the urine
Occludin: (Secondary)
- 65 kDa (bigger)
- 2 isoforms (alternative splicing)
- Localization to tight junctions is regulated by phosphorylation in epithelial and endothelial cells
- Not as essential as claudins
*Both have 4 alpha-helical TM segments with 2 extracellular loops
What phenotype does an Occludin deficient mice show?
- Chronic inflammation, gastric epithelium calcification → not easily explained by barrier function
Occludins might be involved in epithelial differentiation
What protein is responsible for anchorage to the cytoskeleton of claudin and occludin?
ZO proteins = Zonula Occludens → bind to actin filament
*Tight junction complexes connect to actin filaments
What is the molecular weight of 1 amino acid?
0.11 kDa ~ 100 Da
What are the 3 major types of cytoskeleton fibers?
- Actin filaments → made out of actin → involved in tight junctions
- Intermediate filaments → made out of Keratin, Vimentin, Desmin → involved in tight junctions
- Microtubules → made out of tubulin → not involved in tight junctions
What is the impact of a mutation on Cldn-1 gene (claudin gene)?
Causes Neonatal ichtyosis and sclerosing cholangitis
Neonata ichtyosis → heterogenous family of at least 28 mostly genetic skin disorders → dry, thickened, scaly or flaky skin
Cholangitis → infection of the common bile duct (tube that carries bile from the liver to the gallbladder and intestines)
*Tight junction-associated hereditary disease
What is the impact of a mutation on Cldn-19 gene (claudin gene)?
Hypomagnesemia (low Mg in blood) with hypercalciuria (high Ca in urine) + nephrocalcinosis (disorder causing excess Ca deposited in the kidneys) with visual impairment
*Tight junction-associated hereditary disease
What is the impact of a mutation on ZO-2 gene (ZO-protein gene)?
Familial hypercholamenia (FHC) → elevated serum bile acid concentrations, itching and fat malabsorption
*Tight junction-associated hereditary disease
Why is it important to have anchoring junctions?
- Cell is flimsy
- Transmission of force
- Tension bearing cytoskeleton
*Anchoring provides stability to the cell
In what tissues are anchoring junctions more abundant?
Widely distributed in animal tissues → most abundant in muscle, heart, epidermis, epithelia (intestinal, skin cells)
What are the 2 main protein classes involved in anchoring junctions?
- TM adhesion proteins:
- Cytoplasmic tail + TM + extracellular domain
*The extracellular domain can bind to another TM adhesion protein or the ECM - Intracellular anchor proteins:
- connect to actin and intermediate filaments