Extracellular Matrices

Question 1

What is ECM ?

Answer 1

Extracellular matrix is a complex network of proteins and other molecules located outside the cells in tissues.

Question 2

What is the function of a plant cell wall ?

Answer 2

Provides rigidity and strength.
It work in association with turgor pressure.

Question 3

Describe the plant cell wall structure and composition

Answer 3

It is a 3 layered structure:
1. Primary cell wall
2. Secondary cell wall
3. Middle lamella

Question 4

What is the middle lamella of plant ECM ?

Answer 4

It is a uniform and continuous layer between adjacent cell walls
It is a ‘glue’ that binds adjacent plant cells together.

Question 5

What is the middle lamella made of ?

Answer 5

It is made of pectins, which are gel like polysaccharides.

Question 6

What is the primary cell wall of plant ECM ?

Answer 6

It is the first cell wall to be produced.
It is expandable to allow the cell to grow and is permeable to allow passage of nutrients and air.

Question 7

What is the primary cell wall composed of ?

Answer 7

1. Cellulose- straight chains of beta glucose, which form microfibrils for strength
2. Hemicellulose- branched chain that cross links cellulose microfibrils to increase tensile strength
3. Pectin
4. Proteins- involved in wall remodelling

Question 8

What is the secondary plant cell wall ?

Answer 8

A thick layer formed between the plasma membrane and the primary cell wall.
It is made after the cell has stopped growing.

Question 9

What is the secondary cell wall composed of ?

Answer 9

1. Cellulose
2. Lignin
3. Pectin isn’t always present
4. Hemicellulose
   No protein present

Question 10

What are the 3 ECM classes in animals ?

Answer 10

1. Fibrous proteins
2. Proteoglycans and GAGs
3. Glycoproteins

Question 11

What is the most abundant protein in mammals?

Answer 11

Collagen

Question 12

Describe the composition of collagen

Answer 12

A triple-stranded helix, which is made of three collagen alpha-chains.
Rich in glycine and proline.
Hydrogen bonds stabilise interactions between helices.
Provides an extremely stable structure.

Question 13

How many classes of collagen are there ?

Answer 13

28

Question 14

Name some different classes of collagen

Answer 14

1. Fibrillar
2. Network
3. Anchoring
4. Transmembrane
5. Beaded-filament
6. Multiplexins

Question 15

What class does type 1 collagen belong to?

Answer 15

Fibrillar collagen

Question 16

What do you call a chain of collagen with 3 identical alpha chains ?

Answer 16

Homotrimer

Question 17

How is type 1 collagen synthesised ?

Answer 17

1. Translation
2. Proline and lysine hydroxylstion
3. Triple helix formation
4. Secretion
5. Cleavage of N and C terminals
6. Cross link formation

Question 18

What class does type IV collagen belong to ?

Answer 18

Network collagen

Question 19

Describe network collagen (type IV)

Answer 19

Contains a triple helix with several non-triple helical sections
Does not form fibrils

Question 20

What are the functions of type IV collagen ?

Answer 20

Main collagen in basement membrane.
1. Structural support
2. Cell adhesion
3. Filtration barrier

Question 21

What do elastic fibres do ?

Answer 21

They provide elasticity to tissues and enable recoil after stretch.
They are interwoven into collagen fibres to avoid tearing.

Question 22

What are elastic fibres made of ?

Answer 22

Elastin and microfibrils (mostly fibrillin)
Elastin molecules are joined by covalent bonds to generate a cross-linked network

Question 23

What are the differences between collagen and elastin ?

Answer 23

1. Collagen has high tensile strength, elastin doesn’t
2. Collagen has rigid fibres, elastin has flexible coiled structures

Question 24

What is GAG ?

Answer 24

Glycosaminoglycan

Question 25

What are GAG and proteoglycans?

Answer 25

Highly hydrated and gel like matrices

Question 26

Describe the structure of GAG

Answer 26

It is an unbranched polysaccharide chain made of repeating disaccharide units. It is highly negatively charged and hydrophilic. Gel like so withstands compressive forces.

Question 27

What is hyaluronan ?

Answer 27

Hylauronic acid The simplest form of GAG Bulky and hydrated

Question 28

What are the functions of hylauronic acid ?

Answer 28

1. Maintains osmotic pressure by cation binding 2. Lubricant 3. Wound healing

Question 29

What are proteoglycans?

Answer 29

A protein core with a GAG chain covalently binded to the protein core

Question 30

What is aggrecan ?

Answer 30

A proteoglycan. All interactions are non covalent. Major component of cartilage that provides compressive strength. Under compression water is displaced, upon relaxation water rebinds aggrecan.

Question 31

What are glycoproteins ?

Answer 31

Proteins + sugar side chain They contain a short, branched oligosaccharide side chain Have adhesive properties.

Question 32

What is fibronectin ?

Answer 32

Multidomain glycoprotein that binds to different substrates

Question 33

What are the functions of fibronectin ?

Answer 33

1. Organisation and stabilisation of ECM network 2. Adhesion which enables cell attachment and migration

Question 34

What is laminin ?

Answer 34

A glycoprotein with a heterotrimer structure. Found in basement membranes and needed for cell adhesion and tissue organisation.