CB18: Proteins of ECM Flashcards
How many types of collagen are there?
28
What are the 4 most common types of collagen & where are they found?
Type I: found in skin, tendons & bones.
Type II: found in cartilage.
Type IV: found in basement membranes.
Type XI: found in bones & skin.
What is laminin?
A sheet-like network protein found in basement membranes that forms complexes with collagen type IV.
What is tenascin?
A protein that regulates tissue interactions during foetal development & oncogenesis.
What is fibronectin?
A protein involved in the guidance of migrating cells during embryogenesis & adhesion of cells to matrix.
What is 1 collagen molecule made of?
3 polypeptide alpha chains with glycine as the third amino acid.
How are collagen fibres made from collagen molecules?
Collagen molecules form covalent cross-links between lysine residues of collagen molecules. This forms collagen fibrils, which are then bound together to form collagen fibre.
How do collagen fibres form intermolecular cross-links?
The enzyme lysyl oxidase deaminates some lysines & hydroxylysines. This forms highly reactive aldehyde groups which can react with other lysines/hydroxylysines to form covalent bonds.
Where are intermolecular cross-links formed in collagen fibres?
In non-helical segments at the end of the molecules.
What is the role of proteoglycans in cartilage?
To resist compressive forces & allow rapid diffusion of nutrients, metabolites & hormones between blood & tissue cells.
What do proteoglycans do
They form ground substance to embed fibrous proteins.
How do proteoglycans give ground substance its gel-like consistency?
Proteoglycans are negatively charged so they attract cations and water is drawn in by osmosis, giving ground substance its gel-like consistency.
What are proteoglycans composed of?
Glycosaminoglycans linked to a core protein. They associate with each other & other components of ECM.
What are glycosaminoglycans?
They are polysaccharides composed of repeating disaccharides. They have sulphate/carboxyl groups so they are negatively charged.
What is the composition of the disaccharides in glycosaminoglycans?
- First disaccharide: amino sugar.
- Second disaccharide: uronic acid.
What are the characteristics of hyaluronan?
- It’s a special type of GAG that is not covalently linked to a core protein. It is not sulphated.
What is hyaluronan composed of?
Identical disaccharides.
What’s the size of hyaluronan?
25 000 monomers which is huge.
What is hyaluronan used for?
It facilitates cell migration during development & repair. It’s used in joint fluid & wound healing.
What are the 4 main groups of GAGs?
- Hyaluronan (special type of GAG)
- Chondroitin sulphate & dermatan sulphate
- Heparan sulphate
- Keratan sulphate
How does the structure of elastin allow it to stretch & relax?
Elastin is made of hydrophobic molecules that form extracellular extensible fibres. They are arranged in discontinuous sheets in the ECM.
How are proteins of the ECM used in soft tissues?
Soft tissues have little ECM so they can remain soft.How are proteins of the ECM used in
How are proteins of the ECM used in bone?
ECM proteins become calcified using calcium phosphate crystals to make it rock-hard.
How are proteins of the ECM used in tendons?
ECM proteins are rope-like to give tendons an enormous tensile strength + flexibility.
How are proteins of the ECM used in the vitreous humour of the cornea?
ECM proteins become transparent & soft.
How are proteins of the ECM used in cartilage?
ECM proteins are tough & shock-absorbent.
