Lecture 17

Question 1

What is the ECM?

Answer 1

The extracellular matrix (ECM) is the non-cellualr component present within all tissues and organs.

Question 2

What does the ECM bear?

Answer 2

The ECM directly bears mechanical stresses of tension and compression

Question 3

Proteins from the ECM are _____?

Answer 3

Proteins from the ECM are secreted.

Question 4

What is the function of the ECM?

Answer 4

The ECM is a large network of proteins and other molecules that surround, support and give structure to cells and tissues.

Question 5

What are some examples of proteins found in the ECM?

Answer 5

• Collagen
• Proteoglycans
• Laminin

Question 6

What are the three proteins that make the ECM?

Answer 6

• Proteoglycans, fibrous proteins, and glycoproteins.

Question 7

Examples of proteoglycans and GAGs?

Answer 7

• Hyaluronan/Hyaluronic acid
• Perlecan
• Decorin
• Aggrecan

Question 8

Examples of fibrous proteins?

Answer 8

• Type IV collagen
• fibrillar collagen

Question 9

Examples of glycoproteins?

Answer 9

• Laminin
• nidogen
• fibronectin

Question 10

Differences between proteoglycans and glycoproteins?

Answer 10

Proteoglycans have huge oligosaccharide chains, whereas glycoproteins generally contain relatively short oligosaccharide chains.

Question 11

What are GAGs?

Answer 11

Glycosaminoglycans (GAGs) are unbranched polysacharide chains made of repeating disaccharide units.

Question 12

What is hyaluron?

Answer 12

Hyaluronan (hyaluronic acid/hyaluronate) is the simplest of the GAGs. It is made out directly from the cell surface by and enzyme complex embedded in th plasma membrane.

Question 13

What is the function of hyaluronan?

Answer 13

Hyaluronan is a space filler and compression protector.

Question 14

One side chain of a proteoglycan must be…?

Answer 14

At leasrt one of the sugar side chains of a proteoglycan must be a GAG.

Question 15

Where does o-linked glycosylation occur?

Answer 15

O-linked glycoylation occurs at the Golgi

Question 16

Where does GAG addition occur?

Answer 16

The addition of GAG happens outside of the cell.

Question 17

Glycosaminoglycans absorb…?

Answer 17

Glycosaminoglycans absorb large quantities of water, causing them to swell.
- The sugars absorb a lot of water

Question 18

What is an example of fibrous proteins?

Answer 18

Collagen is an example of fibrous protein

Question 19

Collagen molecules are…?

Answer 19

A collagen molecule is a long, stuff, triple stranded helical structure in which three collagen polypeptide chains called a-chains bind.

Question 20

Collagen molecules assemble into?

Answer 20

Collagen molecules assemble at the ECM into thick, long collagen fibres, which we use structurally.
- Fibres are made of fibrils (not cylindrical)

Question 21

Formation of procollagen molecule occurs where?

Answer 21

Collagen molecule formation occurs in the ER lumen

Question 22

Collagen fibril and fiber formation occurs where?

Answer 22

The formation of collagen molecules, fibrils, and fibers occurs after the secretion from the cell.

Question 23

How do collgane fibres assemble?

Answer 23

Collagen fibers assemble by cross linking collagens
- They can be intermolecular (within molecule) or intramolecular (between molecules)

Question 24

Stretching and collagen fibrils, defects?

Answer 24

Collagen fibrils form structures that resist stretching forces.
- Defects in the structure or processing of the protein collagen affects the elasticity of the connective tissue.

Question 25

Collagens fit into what two main categories?

Answer 25

Not all collagens will form giant fibrils whilst some will be fibril-associated collagens.

Question 26

Matrix glycoproteins are what kind of proteins?

Answer 26

Many matrix glycoproteins are large scaffold proteins (bind many things at once, stabilizing them) that are containing mutliple copies of specific protein-interaction domains.

Question 27

Features of matrix glycoproteins?

Answer 27

- multiple domains - bind to other matrix molecules and cell receptors - They have cross linking functions

Question 28

Glycoprotein domains?

Answer 28

Glycoproteins have multiple domains and crosslink other matrix molecules and cell receptors. - Repeat domains are a piece of proteins that forms a distinct shape and has a distinct function.

Question 29

What is fibronectin?

Answer 29

Fibronectin is an example of a glycoprotein: - Fibronectin is a dimer joined by disulfide bonds

Question 30

What is laminar and what is it composed of?

Answer 30

Laminin is a large glycoprotein composed of three chains. - It links the ECM to cell surface receptors.

Question 31

What is the role of integrins?

Answer 31

Integrins connect the ECM to the cytoplasm - they have two conformations - they are dimers - the cytoplasmic region binds talin

Question 32

What does the ECM provide for the cell?

Answer 32

The ECM provides essential physical scaffolding for the cell.

Question 33

What are integrins?

Answer 33

Integrins are transmembrane heterodimers that link ECM to actin cytoskeleton

Question 34

Extracellular poritons of integrin?

Answer 34

The extracellular portions of integrin bind ECM proteins like fibronectin or collagen

Question 35

Intracellular integrin tail role?

Answer 35

The intracellular integrin tails bind to a complex of adaptor proteins that link the actin cytoskeleton like talon and viniculin

Question 36

Integrin conformations?

Answer 36

Integrins switch brtween active and inactive conformations

Question 37

Active integrin?

Answer 37

Binding sites are exposed

Question 38

Inactive integrin?

Answer 38

Bidning sites are hidden

Question 39

Integrins can be activated how?

Answer 39

Integrins can be activated from the otuside or from the inside: 1. binding to a ECM substrate 2. Binding to talin in the inside

Question 40

What happens to epithelia without integrins?

Answer 40

Epithelia without integrins detach from the basal lamina - We see this in flies that end up with a bubble strcutre on their wings

Question 41

What do integrin clusters form?

Answer 41

Integrins cluster to form strong and dynamic connections to the ECM called focal adhesion sites.

Question 42

How dynamic are integrins?

Answer 42

Integrins are very dynamic! They form clusters called focal adhesion sites

Question 43

What are focal adhesions?

Answer 43

Focal adhesions are large macromolecular assemblies that form mechanical links between intracellular actin bundles and the ECM. - Talin and viniculin are the main components.