ECM

Question 1

4 functions of the extracellular matrix

Answer 1

1. physical strength/ structural support
2. cell shape and behaviour
3. storage of growth factors
4. tissue repair

Question 2

the 2 major types of molecules in the ECM

Answer 2

fibrillar proteins and glycosaminoglycans

Question 3

what are glycosaminoglycans

Answer 3

glycosaminoglycans are polysaccaride chains covalently bound to proteins to form a proteoglycan

Question 4

the 2 kinds of fibrillar proteins and their functions

Answer 4

collagens for structure

fibronectin as adhesive glycoprotein

Question 5

what is the structure of fibrillar collagen

Answer 5

3 polypeptide chains wound around each other to form a superhelix structure

Question 6

what is the amino acid sequence of collagen

Answer 6

glycine-X-Y repeated sequence
X is often proline
Y is often hydroxyproline

Question 7

how does glycine’s structure contribute to its importance in collagen

Answer 7

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

Question 8

why is hydroyxproline so important

Answer 8

it stabilises the triple helix by forming additional hydrogen bonds and holding proline ring in a conformation that helps stabilise the helix

Question 9

3 different types of collagen

Answer 9

fibril forming
fibril associated
networking (fishnet) making

Question 10

intracellular steps of collagen synthesis

Answer 10

1. cleavage of signal peptide on N terminus
2. hydroxylation of proline and lysine residues
3. glycosylation of proline resides
4. N and C propeptides of polypeptides facilitate winding into helices, chaperone proteins prevent misfolding
5. pacakged into vesicles and further processed in Golgi

Question 11

extracellular steps of fibrillar collagen synthesis

Answer 11

1. cleavage of the N and C propeptides
2. self assembly of the triple helical rods into long fibrils
3. crosslink formation between the fibrils
4. binding of fibril associated proteins

Question 12

how are collagen crosslinks formed

Answer 12

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

Question 13

why is vitamin c so important

Answer 13

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

Question 14

how do collagen fibrils associate with other proteins

Answer 14

proteoglycans and non -fibrillar collagens regulate orientation and size of the fibrils

Question 15

what allows connective tissues to stretch and what do they contain

Answer 15

elastic fibres which are not related to collagen

these contain elastin and glycoproteins like fibrillin