Lecture 23 - The extracellular matrix Flashcards
What is the ECM?
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
What are the 3 types of proteins that make the ECM?
proteoglycans & GAGs, fibrous proteins, and glycoproteins
What are glycosaminoglycans (GAGs)?
they are unbranched polysaccharide chains made of repeating disaccharide units
What is hyaluronan?
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
Proteoglycans and GAGs
at least of the sugar side chains of a proteoglycan must be a GAG
- addition of GAG happens outside the cell
Glycosaminoglycans absorb large quantities of _______ and swell
water
What’s an example of a fibrous protein?
collagen
Collagen molecule
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
What do defects in the structure or processing of the protein collagen affect?
they affect the elasticity of the connective tissue b/c collagen fibers form structures that resist stretching forces
Matrix glycoproteins
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
What are scaffolding proteins?
proteins that bind to other proteins and keep them together
What is fibronectin?
- a glycoprotein
- a dimer joined by disulfide bonds
Laminin
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
Integrins connect the ____ to the _____
ECM; cytoplasm
Integrin structure and function
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)
Conformations of integrin
switches between active and inactive
- active: binding sites exposed
- inactive: binding sites hidden
Where can integrins be activated?
from the outside or the inside
1. binding to an ECM substrate
2. binding to talin on the inside
What happens to epithelia without integrins?
they detach from the basal lamina
- makes bubbles/blisters in skin
What do integrins cluster to form?
strong and dynamic connections to the ECM called focal adhesion sites
What are focal adhesions?
large macromolecular assemblies that form mechanical links between intracellular actin bundles and the ECM
- talin and vinculin are the main components
