lecture 13 - the Extra cellular matrix Flashcards
What is a definition of the extra cellular matrix?
extracellular matrix (ECM) any substance produced by cells and secreted into the extracellular space within the tissues.
What is the primary function of the ECM?
ECM provides physical support for cells and a linkage between different cells or tissues
What is another function of the ECM?
Cell Motility – it forms a substrate on which cells can move and furthermore it provides cues that guide the direction of movement
What is the basic cellular organisation In animals?
- epithelial tissue
- connective tissue
What is the general composition the ECM?
- consists of scattered cells
- consists of collagen fibers (protein) cross-linked by accessory proteins in a matrix of proteoglycans (protein + polysaccharides)
What is the scant ECM?
- consists of layers of cells closely bound to one another to form protective sheets
What are the layers of the ECM?
- epithelial cells
- basal lamina
- collagen
What is the purpose of the basal lamina?
provides a base for the cells to sit on and acts as a molecular sieve and substrate for migrating cells
What is the ECM in plants?
The cell wall
What is the composition of the cell wall?
consists of cellulose fibers (polysaccharide) cross-linked with hemicellulose in a matrix of highly branched polysaccharides (e.g. Pectin)
How does the ECM differ between plants and animals?
plants contain polysaccharide fibres animal ECM has fibres made of protein whilst Animal ECM contains COLLAGEN & ELASTIN
How many genes are in mammals which make up the collagen in the body?
42 different genes
What proportion of the body does the % of collagen make up?
25%
How is collagen formed?
- single collagen polypeptide chain
- triple- stranded collagen molecule
- collagen fibril
What are the 5 steps of collagen formation steps within the cells?
- synthesis of a pro - alpha chain
2 .- hydroxylation of selected prolines and lysines
- synthesis of a pro - alpha chain
- glycosylation of selected hydroxylysines
- self assembly of three pro- alpha chains
5.- pro collagen triple helix formation
- self assembly of three pro- alpha chains
What are collagen helical regions composed of?
composed of Gly-X-Y repeats, where X and Y can be any AA, but usually Pro and HydroxyPro, and less commonly Lys and HydroxyLys
What does elastin do?
- provides elasticity to tissues
How is elastin composed?
composed of large filaments with lots of random coils that can be compared to springs
How is elastin connected?
by cross-linked Lysine or hydroxylysines
What happens when elastin fibres are relaxed?
coiled up
How is the ECM similar to the ECM in plants?
most of the matrix consists of polysaccharides
What is the name of the polysaccharide in plants in the ECM?
pectin
What is the name of the polysaccharide in animals?
Glycosaminoglycans
What are the 3 different types of GLYCOSAMINOGLYCANS?
hyaluronan, chondroitin sulphate, heparan sulphate
What is different about hyaluronan?
- does not form covalent cross linking
What are glycosaminoglycans made of
Disaccharide = glucoronic acid or iduronic acid, and N-acetylglucosamine or N-acetylgalactosamine
The disaccharide is repeated along the chain .
What do the types of connective tissue exist due to variation?
the relative proportion of fibres to cells within the ECM
the number and proportion of different cell types within the ECM
. the proportion and arrangement of the fibres in the ECM
the composition of the non-fibrous component of the ECM
Who was Mr Morris and what was his symptoms?
- had very stretchy skin
- Connective tissue of the dermis is affected
- The component that stops it stretching too far is collagen. - Collagen is rigid won’t stretch too much
- The elastin fibres go much further than the collagen
Why did Mr Morris’s collagen not form?
Failure of conversion of lysine to hydroxylysine by lysyl hydroxylase OR failure to cleave off propeptide termini
=> fibrils and fibres don’t form
What does areolar connective tissue do in the body?
cushions the organs in out body . Made up of elastin and collagen, helps to encase internal organs
What is adipose tissue made up of?
- collagen 3 and reticular fibres
What are tendons and ligaments made up of?
- Dominant feature is not the cells but the collagen fibres
What is the dermis of the skin made up of?
- collagen fibres and fibroblast nuclei
- collagen must be organised in a more variable way due to the skin being able to move more
What is elastic collagen made up?
- elastin fibres
What is different about bone?
Mineralised matrix , calcium rich cystal matrix that is crucial for bond strength
What is the mechanism for scurvy?
Scurvy due to lack of Vit C (Ascorbic acid) essential cofactor for propel hydroxyls that make hyrdoxyPro and which needed for crosslinking of collagen fibres
What are the symptoms of scurvy?
lack of nromal fibrils leads to fragility and bleeding and teeth loss, etc
What does Fibrodysplasia ossificans progressiva
do?
Muscle and connective tissue like tendons are gradually replaced by bone (ossified
