ECM Flashcards
4 functions of the extracellular matrix
- physical strength/ structural support
- cell shape and behaviour
- storage of growth factors
- tissue repair
the 2 major types of molecules in the ECM
fibrillar proteins and glycosaminoglycans
what are glycosaminoglycans
glycosaminoglycans are polysaccaride chains covalently bound to proteins to form a proteoglycan
the 2 kinds of fibrillar proteins and their functions
collagens for structure
fibronectin as adhesive glycoprotein
what is the structure of fibrillar collagen
3 polypeptide chains wound around each other to form a superhelix structure
what is the amino acid sequence of collagen
glycine-X-Y repeated sequence
X is often proline
Y is often hydroxyproline
how does glycine’s structure contribute to its importance in collagen
its the smallest amino acid with one hydrogen as its side chain
its the only amino acid small enough to fit in middle of the triple helix so allows the 3 polypeptide chains to intertwine tightly
why is hydroyxproline so important
it stabilises the triple helix by forming additional hydrogen bonds and holding proline ring in a conformation that helps stabilise the helix
3 different types of collagen
fibril forming
fibril associated
networking (fishnet) making
intracellular steps of collagen synthesis
- cleavage of signal peptide on N terminus
- hydroxylation of proline and lysine residues
- glycosylation of proline resides
- N and C propeptides of polypeptides facilitate winding into helices, chaperone proteins prevent misfolding
- pacakged into vesicles and further processed in Golgi
extracellular steps of fibrillar collagen synthesis
- cleavage of the N and C propeptides
- self assembly of the triple helical rods into long fibrils
- crosslink formation between the fibrils
- binding of fibril associated proteins
how are collagen crosslinks formed
there are short segments of hydroxylysine at the end of collagen molecules (not associated with the triple helix)
Lysyl oxidase catalyses the formation of covalent intermolecular crosslinks
why is vitamin c so important
it is a cofactor for propyl hydroxylase which catalyses formation of hydroxyproline from proline
hydroxyproline is crucial for stability in collagen
scurvy leads to gradual loss of collagen
how do collagen fibrils associate with other proteins
proteoglycans and non -fibrillar collagens regulate orientation and size of the fibrils
what allows connective tissues to stretch and what do they contain
elastic fibres which are not related to collagen
these contain elastin and glycoproteins like fibrillin