ECM Flashcards
ECM
any substance produced by cells and secreted into the extracellular space within the tissues
Why is the ECM important structurally
provides physical support or cells and linkage between cells and tissues
Why is the ECM important for cell motility
acts as a substrate on which cells can move and provides cues that direct movement
connective tissue structure
dominant feature is ECM
cells scattered throughout
consists of collagen fibres cross linked by accessory proteins in a matrix of proteoglycans (protein + polysaccharides)
epithelial tissue structure
dominant feature is cells, which lie directly in contact with one another
layers of cells closely bound to form protective sheets
What does the ECM form in epithelial tissue, and what is the function
basal lamina
Provides a base for cells to sit on and acts as a molecular sieve and substrate for migrating cells
Provides interface to underlying connective tissue
ECM in plants
consists of cellulose fibres (polysaccharide) cross linked with hemicellulose in a matrix of highly branched polysaccharides (pectin)
what does the animal ECM contain
collagen and elastin
difference between ECM in plants vs animals
plants ECM contain polysaccharide fibres vs animal ECM has fibres made of protein
what happens to collagen under tension
fibres strengthen, resists tensile forces
structure of collagen
3 polypeptide chains wrapped around each other
Bind to each other laterally via cross links to form collagen fibrils. Fibrils assemble to form collagen fibres
Fibres in 2 orthogonal orientations, which provides strength.
Type II collagen cross linked by Type IX to from mesh
process of making collagen
Collagen has a simple structure- Gly, X, Y triple amino acid repeat
X and Y usually lysine and proline.
1. Synthesis of pro-alpha chains on ribosome in rough ER
2. Hydroxylation of selected prolines and lysines (hydroxy modified AAs are the basis of cross linking between collagens fibres
3. Glycosylation of some hydroxylysines
4. Self assembly of 3 pro-alpha chains. Have a propeptide on each end, keeps pro-collagen in solution and prevents formation of fibrils and fibres
5. Triple helical pro-collagens bundled up into vesicles, fuse with the CSM and released outside cell. vesicles fuse to form a tube when fusing with CSM
6. Peptidases cleave off peptide regions outside the cell
7. Assembly to form fibrils and fibres
Elastin
provides elasticity to tissues
composed of large filaments with random coils, connected by hydroxylysines
How is the ECM in animals similar to the ECM in plants
most of the matrix consists of polysaccharides
plants = pectin
animals = GAGS
GAGS
Glycosaminoglycans
repeating disaccharide with a limited number of sugars
very -ve charge
hydrophilic (carboxyl group attracts water)
form linear chains
linked to non-fibrous proteins-proteoglycans
why do many types of connective tissue exist
due to variation in the relative proportion of fibres to cells within the ECM
Number and proportion of different cell types within the ECM
Proportion and arrangement of the fibres in teh ECM
Composition of non-fibrous component of the ECM
areolar connective tissue
provides cushioning around tissue/muscles
lots of elastin
collagen not very densely distributed
loose connective tissue- link between organs eg dermis to muscles underneath
Adipose tissue
dominated by cells that accumulate fat droplets -adipocytes
tendons and ligaments
collagen fibres are aligned parallel to each other, so when force is applied in a particular direction, this optimises strength of the fibres
Orientated specifically along line of force
Dermis of the skin
Lots of stress/force
can be pulled in any direction
Lots of collagen, secreted by fibroblasts, orientation varies
elastic cartilage
lots of elastin
Bone
dominated by a calcium-based matrix, not fibres
bone secreted by osteocytes
Scurvy
due to lack of Vit C
essential cofactor prolyl hydroxylases that make hydroxyproline, needed for crosslinking of fibres
Lack of normal fibrils leads to fragility and bleeding and tooth loss etc
proteoglycans
group of glycoproteins that cushion cells and bind a wide variety of extracellular molecules
Usually consist of glycoproteins containing covalently attached GAGS
What are most ECM components produced by
fibroblasts
