ECM

Question 1

ECM

Answer 1

any substance produced by cells and secreted into the extracellular space within the tissues

Question 2

Why is the ECM important structurally

Answer 2

provides physical support or cells and linkage between cells and tissues

Question 3

Why is the ECM important for cell motility

Answer 3

acts as a substrate on which cells can move and provides cues that direct movement

Question 4

connective tissue structure

Answer 4

dominant feature is ECM
cells scattered throughout
consists of collagen fibres cross linked by accessory proteins in a matrix of proteoglycans (protein + polysaccharides)

Question 5

epithelial tissue structure

Answer 5

dominant feature is cells, which lie directly in contact with one another
layers of cells closely bound to form protective sheets

Question 6

What does the ECM form in epithelial tissue, and what is the function

Answer 6

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

Question 7

ECM in plants

Answer 7

consists of cellulose fibres (polysaccharide) cross linked with hemicellulose in a matrix of highly branched polysaccharides (pectin)

Question 8

what does the animal ECM contain

Answer 8

collagen and elastin

Question 9

difference between ECM in plants vs animals

Answer 9

plants ECM contain polysaccharide fibres vs animal ECM has fibres made of protein

Question 10

what happens to collagen under tension

Answer 10

fibres strengthen, resists tensile forces

Question 11

structure of collagen

Answer 11

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

Question 12

process of making collagen

Answer 12

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

Question 13

Elastin

Answer 13

provides elasticity to tissues

composed of large filaments with random coils, connected by hydroxylysines

Question 14

How is the ECM in animals similar to the ECM in plants

Answer 14

most of the matrix consists of polysaccharides
plants = pectin
animals = GAGS

Question 15

GAGS

Answer 15

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

Question 16

why do many types of connective tissue exist

Answer 16

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

Question 17

areolar connective tissue

Answer 17

provides cushioning around tissue/muscles
lots of elastin
collagen not very densely distributed
loose connective tissue- link between organs eg dermis to muscles underneath

Question 18

Adipose tissue

Answer 18

dominated by cells that accumulate fat droplets -adipocytes

Question 19

tendons and ligaments

Answer 19

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

Question 20

Dermis of the skin

Answer 20

Lots of stress/force
can be pulled in any direction
Lots of collagen, secreted by fibroblasts, orientation varies

Question 21

elastic cartilage

Answer 21

lots of elastin

Question 22

Bone

Answer 22

dominated by a calcium-based matrix, not fibres

bone secreted by osteocytes

Question 23

Scurvy

Answer 23

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

Question 24

proteoglycans

Answer 24

group of glycoproteins that cushion cells and bind a wide variety of extracellular molecules
Usually consist of glycoproteins containing covalently attached GAGS

Question 25

What are most ECM components produced by

Answer 25

fibroblasts