Extracellular Matrix Flashcards
What is the extracellular matrix made up of?
Connective tissue - fibres, fibroblasts and ground substance.
What is collagen?
A fibrous, rope-like molecule that provides tensile strength to all tissues in the body.
Example of collagen l distribution
In skin, tendons, ligaments, cornea, internal organs
Example of collagen ll distribution
Cartilage, notochord
What is the structure of collagen?
A long, stiff triple helix structure where 3 collagen molecules twist around each other to form a superhelix. Triple helices combine to form collagen fibrils, and then fork collagen fibres.
How are collagens covalently cross linked?
Via lysyl hydroxylase and prolyl hydroxylase. Both require iron and vitamin C.
Which cell produces collagen normally/in bone?
Normally - fibroblasts.
In bone - osteoblasts.
Which cell is involved in scar formation?
Fibroblasts
What is the precursor of collagen?
Procollagen.
Why is collagen made as a precursor first?
Produced as procollagen inside the cell, which has additional peptides so will not be assembled into fibrils inside the cell. Only extracellular enzymes (procollagen proteinases) can cut off these peptides to allow assembly of collagen fibres.
What is Ehlers-Darlos syndrome?
Mutation of procollagen proteinases, so collagen fibres don’t assembly properly in skin and other tissues.
How can cells degrade the extracellular matrix?
Matrix metalloproteinases degrade ECM so macrophages can invade tissue during infection.
How do cells attach to the ECM?
As cells attach poorly to bare collagen, they attach to fibronectin instead via transmembrane receptors called integrins. Integrins attach to actin cytoskeleton to give tensile strength.
How does the ECM resist compression?
Using glycosaminoglycans, which resist compression and fill space
What do glycosaminoglycans form?
They form gels that make up the ground substance
What are the roles of glycosaminoglycans in the ECM?
Space filling
Resist compression
Regulate molecular transport through ECM
Bind and act as a reservoir of growth factors that signal to cells
Regulate cell migration and movement through the ECM
What are the two surfaces of epithelial sheets?
Basal and apical
What is the basal lamina made up of?
Type lV collagen and laminin, which connects basal lamina to integrins in the epithelial cells
What are tight junctions?
A leak proof seal between cells
What are adherens junctions?
Joins an actin bundle of one cell to a similar bundle in a neighbouring cell
What are desmosomes?
Joins intermediate filaments of one cell to those in a neighbour
What are henidesmosomes?
Anchors intermediate filaments in a cell to basal lamina
What are gap junctions?
Channels that allow small water soluble molecules to pass from cell to cell
What are tight junctions made of?
Claudins and occludins
Which cytoskeleton linked junctions provide mechanical strength to epithelial sheets?
Adherens junctions, desmosomes, hemidesmosomes
How are desmosomes formed?
Connect via cadherins to the keratin intermediate filaments to provide strength to epithelial sheets
How are hemidesmosomes formed?
Integrins link basal lamina to cell via the keratin filaments
