Cell Adhesion 2 - Adhesion to the ECM

Question 1

is adhesion to the ECM permanent?

Answer 1

• no
• as cells need to migrate

Question 2

What are integrins?

Answer 2

• connect the cell to the ECM
• heterodimers
• transmembrane proteins
• one end connects to fibronectin which connects to ECM
• other end attaches to adaptor proteins which attach to actin (cytoskeleton)

Question 3

Why is integrin connected to the cytoskeleton?

Answer 3

without this connection it would be flimsy

Question 4

What is fibronectin?

Answer 4

• dimer connected by disulphide bridge
• cell attachment site - where integrins attach
• ECM binding site - where collagen binds

Question 5

What is the structure of integrin?

Answer 5

• heterodimer
  
  • alpha sub-unit
  • beta sub-unit

Question 6

What is the innactive conformation of integrin?

Answer 6

folded

Question 7

What is the active conformation of integrin?

Answer 7

• stretched
• when bound to fibronectin

Question 8

Explain integrin regulation

Answer 8

inactive - folded
active - stretched

• reversible change - allows cells to move across ECM

Question 9

How many different kinds of integrin do humans have?

Answer 9

24

Question 10

how do integrins coordinate cell movement?

Answer 10

• new attachments made at front of cell
• old adhesions released at the back
• actin forms bonds with ECM in direction of movement and releasing them at the back

Question 11

What is the role of collagen in the ECM?

Answer 11

tensile strength - resist stretching

Question 12

What is the role of glycosaminoglycans (GAGs)

Answer 12

• resist compression - opposite of collagen

Question 13

What is the structure of proteoglycans?

Answer 13

glycosaminoglycans (GAGs) join to core protein

Question 14

How do glycosaminoglycans resist compression?

Answer 14

• GAGs are negative
• attract cations in the ECM
• draw in water
• swelling pressure
• resisting compression

Question 15

how do collagen and GAGs work together in the ECM?

Answer 15

• tension in collagen
• balanced by GAG swelling
• resulting matrix is tough and resistant to pressure

Question 16

Name a body part glycosaminoglycans are common?

Answer 16

cartilage

Question 17

Are GAGs hydrophilic or hydrophobic?

Answer 17

hydrophilic
- space fillers in connective tissue

Question 18

What are others functions of proteoglycans?

Answer 18

• binding growth factors
• controlling migration of cells through ECM

Question 19

Explain tissue specific ECM composition

Answer 19

dense connecting tissues (tendon and bone) -> les GAG, more collagen. CaPO4 crystals in bone
vitreous humour -> made almost entirely of GAG, very little collagen

Question 20

What is an epithelium?

Answer 20

a sheet of cells joined together side by side. It covers all external surfaces and lines all internal cavities

Question 21

What are 4 different forms of epithelia and their functions and where you would find them?

Answer 21

columnar - secretion / absorption - intestinal lining

cuboidal - secretion / absorption - lining of kidney tubules

squamous - filtration - lining of lung

stratified - protection - epidermis of the skin

Question 22

What is the basal lamina?

Answer 22

• thin tough sheet of ECM
• separates epitaxial cells from collagen fibres in connective tissue

Question 23

where’d epithelial cells sit?

Answer 23

on the basal lamina

Question 24

What is the structure of the basal lamina?

Answer 24

• type IV collagen and laminin
• collagen supplied by underlying stromal cells (connective tissue)
• laminin is supplied by overlying epithelial tissue

Question 25

What are stromal cells?

Answer 25

mesenchymal cells that make connective tissue

Question 26

What are mesenchymal cells?

Answer 26

Cells that differentiate into connective tissue

Question 27

What is the structure of laminin?

Answer 27

heterotrimers made of 3 sections

Question 28

What is the role of laminin?

Answer 28

- interacts with proteins such as integrin - provides adhesive sites for integrins located in the basal membrane of epithelial cells - does a similar job to fibronectin in the connective tissue

Question 29

Explain epithelial polarity

Answer 29

two faces: - apical - exposed to the lumen, air and bodily fluids - basal - connected to the basal lamina

Question 30

Explain epithelial polarity in the gut

Answer 30

- absorptive epithelial cells - secretory goblet (mucous) epithelial cells - different functions in same epithelial sheet - cells are polarised

Question 31

What are tight junctions?

Answer 31

- segregate membrane proteins - prevents membrane proteins moving around the cell, maintaining its polarity

Question 32

What is the role of tight junctions in epithelial sheets?

Answer 32

- allows them to function as barriers - binds epithelial cells to prevent leakage

Question 33

How has the role of tight junctions in epithelial cells been proven?

Answer 33

- extracellular tracers stopped by tight junctions

Question 34

What forms tight junctions?

Answer 34

- occluding - claudin

Question 35

Explain the role of tight junctions in the gut

Answer 35

- Na+ active transport of glucose from the gut lumen - passive transport into the bloodstream - tight junctions prevents two transporters moving around the cell, maintaining polarity