Lecture 23 - The extracellular matrix

Question 1

What is the ECM?

Answer 1

the non-cellular component present within all tissues and organs
- its a large network of secreted proteins and other molecules that surround, support, and give structure to cells and tissues

Question 2

What are the 3 types of proteins that make the ECM?

Answer 2

proteoglycans & GAGs, fibrous proteins, and glycoproteins

Question 3

What are glycosaminoglycans (GAGs)?

Answer 3

they are unbranched polysaccharide chains made of repeating disaccharide units

Question 4

What is hyaluronan?

Answer 4

its the simplest of the GAGs
- it is made directly from the cell surface by an enzyme complex embedded in the plasma membrane
- absorbs a lot of water

Question 5

Proteoglycans and GAGs

Answer 5

at least of the sugar side chains of a proteoglycan must be a GAG
- addition of GAG happens outside the cell

Question 6

Glycosaminoglycans absorb large quantities of _______ and swell

Answer 6

water

Question 7

What’s an example of a fibrous protein?

Answer 7

collagen

Question 8

Collagen molecule

Answer 8

a long, stiff, triple stranded helical structure => made from 3 collagen polypeptide chains called alpha chains

many collagen molecules assemble at the ECM (too large to be secreted through cell) into thick long collagen fibers

Question 9

What do defects in the structure or processing of the protein collagen affect?

Answer 9

they affect the elasticity of the connective tissue b/c collagen fibers form structures that resist stretching forces

Question 10

Matrix glycoproteins

Answer 10

many are large scaffold proteins containing multiple copies of specific protein-interaction domains
- have multiple domains that bind to other matrix molecules and cell receptors
- crosslinking function

Question 11

What are scaffolding proteins?

Answer 11

proteins that bind to other proteins and keep them together

Question 12

What is fibronectin?

Answer 12

• a glycoprotein
• a dimer joined by disulfide bonds

Question 13

Laminin

Answer 13

a large glycoprotein composed of 3 chains and links the ECM to cell surface receptors
- one end interacts with other matrix proteins, the other interacts with cell surface receptors

Question 14

Integrins connect the ____ to the _____

Answer 14

ECM; cytoplasm

Question 15

Integrin structure and function

Answer 15

transmembrane heterodimers that link the ECM to the actin cytoskeleton
- extracellular portion binds ECM proteins like fibronectin or collagen
- intracellular tail binds to a complex of adaptor proteins that link the actin cytoskeleton (talin and vinculin)

Question 16

Conformations of integrin

Answer 16

switches between active and inactive
- active: binding sites exposed
- inactive: binding sites hidden

Question 17

Where can integrins be activated?

Answer 17

from the outside or the inside
1. binding to an ECM substrate
2. binding to talin on the inside

Question 18

What happens to epithelia without integrins?

Answer 18

they detach from the basal lamina
- makes bubbles/blisters in skin

Question 19

What do integrins cluster to form?

Answer 19

strong and dynamic connections to the ECM called focal adhesion sites

Question 20

What are focal adhesions?

Answer 20

large macromolecular assemblies that form mechanical links between intracellular actin bundles and the ECM
- talin and vinculin are the main components