Extracellular Matrix

Question 1

What is the extracellular matrix

Answer 1

Material made by cells released into the exterior

Assembled into 3D structure

Question 2

Common features of plan and animal ECM

Answer 2

structurally complex 
fibrous framework (embedded in gel like background matrix)
- plants are polysaccharide fibres in matrix of pectin and polymers
- animals are fibrous protein fibres in matrix of glycosaminoglycans

Question 3

Describe plant ECM

Answer 3

Cell wall is part of extracellular matrix
Carbohydrates with small amounts of protein
Contains cellulose cross linked by thin hemicellulose fibres
Embedded in gel of negatively charged polysaccharides and pectins

Question 4

Plant cell wall uses

Answer 4

Rigidity
strength
High tensile strength

Question 5

Plant cell wall structure and composition

Answer 5

3 layers
Middle lamella synthesised 1st: secreted by cell onto its surface after cytokinesis in cell divisions
Primary wall 2nd and secondary wall 3rd

Calls can alter wall properties by secreting different materials

Question 6

Composition of middle lamella

Answer 6

Made of pectins and some proteins
Mostly pectic acid (polysaccharides)
- a polymer of galactouronic acid molecules
- is highly hydrated and forms a gel with Ca++ and Mg ++
Also pectin
- larger molecule
-less hydrated but still forms a gel

Question 7

Functions of primary wall

Answer 7

• pushes lamella away from plasma membrane

- is expandable for growth and semi permeable

Question 8

Composition fo primary cell wall

Answer 8

• Cellulose; Straight Chain D glucose bound by hydrogen bonds to form fibres
• Hemicellulose; sugar monomer branching chains that cross link with cellulose = increased tensile strength
• Pectin; gel formed from charged sugar chains and water = compression resistance
• proteins; alter mechanical properties e.g cell expansion and some enzymes e.g. formation and breakdown of wall

Question 9

Composition of secondary wall

Answer 9

-not found in all plants
- made after primary stops expanding
Made of
- cellulose
-lignin (makes less flexible and permeable)
-polysaccharides
-NO proteins or enzymes
- some specific glycoproteins

Question 10

Animal ECM composition

Answer 10

Mostly synthesised specialist cells (connective tissue)
Collagen and elastic fibres = fibrous and elastic recoil
Background matrix: glycosaminoglycans, proteoglycans, (those 2 hold water = jelly like which prevents spread of infection) and glycoproteins

Question 11

Collagen structure

Answer 11

• Alpha chains assemble in 3s to form troop collagen
• This assembles into fibrils = quarter stagger arrangements make long structures with handing pattern
• fibrils form fibres

Question 12

What are the 4 types of collagen

Answer 12

1. Most connective tissues. Most common type
2. Cartilage
3. Prominent in embryonic and repair tissues
4. Basal lamina: subunits assemble into planar sheets and sit beneath epithelial, endothelial and muscle cell surfaces

Question 13

Describe elastin

Answer 13

Made from tropelastin protein subunits and the glycoprotein fibrillin
Assemble and stabilise into elastic fibres and sheets

Question 14

How is hyperelasticity formed

Answer 14

Is elastin works and collagen doesn’t

Question 15

Glycosaminoglycans composition

Answer 15

Long unbranched polysaccharide chains made of repeating disaccharides and some sulphate groups
Highly polar so attracts water = compression resistance and lubrication

Question 16

Describe Proteoglycans

Answer 16

Formed from sulphated glycosaminoglycans
May have large number of C and K side chains: aggrecan. That can aggregate in hyaluronan chains
Attracts water = swelling pressure and role in hydration
Can form large structures holding large amounts of water = in joints

Question 17

Describe glycoproteins (Andy fibronectin)

Answer 17

3 short arms = bind to eachother and other molecules to form planar mesh long arm that anchors to basal lamina

Fibronectin = glycoprotein with multiple domains that bind to substrates: links to it other molecules and between molecules

Question 18

Mechanical properties of ECM form glycosaminoglycan/proteoglycans

Answer 18

• collagen: tension resistance
• elastin: recovery form stretch
• compression resistance
• lubrication
• (glycoproteins only) connectors and signallers