Lecture 15: ECM and plant cell wall

Question 1

What is the role of the extracellular matrix in animal tissues?

Answer 1

The architectural basis
Controls mechanical properties

Question 2

How does the ECM control mechanical properties of animal tissues?

Answer 2

Through its protein composition

Question 3

What type of collagen is in connective tissue?

Answer 3

90% is collagen 1
The amount of collagen 1 correlates to tissue stiffness

Question 4

What is the composition of bone?

Answer 4

Collagen 1 which are dark and light rings
Osteoblasts that deposit ECM in bone are black dots
Gaps are calcium phosphate

Question 5

What is collagen made by in bone?

Answer 5

Osteoblasts

Question 6

What is collagen made by in skin and tendons?

Answer 6

Fibroblasts

Question 7

What are the four stages of collagen composition?

Answer 7

1. Procollagen polypeptide chain
2. Triple stranded helical procollagen molecule
3. Collagen fibril
4. Collagen fibres

Question 8

What is procollagen?

Answer 8

Collagen is secreted as procollagen
It can’t form fibrils until its cleaved

Question 9

What is the organisation of procollagen?

Answer 9

Cells deposit it in an oriented way
They rearrange fibres after secretion using integrins in focal contacts

Question 10

What are the results of genetic conditions affecting the ECM?

Answer 10

Abnormally stretchy skin
Brittle bone disease
Skeletal abnormalities

Question 11

What is the role of integrins?

Answer 11

Attach the cell’s cytoskeleton to ECM

Question 12

What determines cytoskeleton linkage?

Answer 12

The type of cell

Question 13

What type of cytoskeleton linkage is in migrating cells?

Answer 13

Focal adhesions

Question 14

What type of cytoskeleton linkage is in epithelial monolayers?

Answer 14

Hemi desmosomes

Question 15

How to fibroblasts attach to the ECM?

Answer 15

Using integrins in focal contacts

Question 16

How do cells bind to collagen?

Answer 16

Using a linker protein

Question 17

What is the linker protein in focal adhesions?

Answer 17

Fibronectin

Question 18

What is the linker protein in the basal lamina?

Answer 18

Laminin

Question 19

In what ways do integrins change during animal cell mitosis?

Answer 19

They are phosphorylated
Weaken their grip on ECM

Question 20

What is the role of the spaces in between collagen?

Answer 20

Filled by gels of polysaccharide and protein
Resist compression

Question 21

What are GAGs?

Answer 21

Large negative polysaccharides
Hydrophilic

Question 22

What are proteoglycans?

Answer 22

Extracellular proteins with covalently linked GAGs

Question 23

What is the process of proteoglycan synthesis?

Answer 23

1. Protein component made in ER
2. Glycosylation starts
3. Glycosylation completed in golgi
4. Delivered to plasma membrane by constitutive secretion

Question 24

What is cartilage?

Answer 24

Tough and resists compression
GAGs generate swelling pressure
Pressure resisted by collagen fibres

Question 25

What is hyalyronan?

Answer 25

Made of carbohydrate and no protein

Question 26

Where does hyaluronan synthesis happen?

Answer 26

Plasma membrane Extruded into extracellular space

Question 27

What are the properties of the plant ECM?

Answer 27

Tough external walls for strength Cell wall resists turgor pressure Resists compression and tension Long fibres oriented along stress lines

Question 28

What are the properties of the primary cell wall?

Answer 28

Laid down first Relatively thin Allows the cell to grow

Question 29

What are the properties of the secondary cell wall?

Answer 29

Composition controlled by cell to determine its properties Hard in wood and flexible in leaves

Question 30

What are the purpose of cellulose fibres in the plant cell wall?

Answer 30

Tensile strength

Question 31

What is the structure of cellulose fibres?

Answer 31

Polysaccharide of D glucose Long fibres with 16 strands Held together with H bonds

Question 32

What is the arrangement of cellulose fibres?

Answer 32

Interwoven with other polysaccharides

Question 33

What is the role of pectin?

Answer 33

Sticks neighbouring cells together Fills spaces and resists compression

Question 34

What is determined by the organisation of cellulose fibres?

Answer 34

The axis of cell growth Tissue structure

Question 35

What is the process of synthesis of cellulose fibres?

Answer 35

1. Cellulose synthase made at ER 2. Transported by golgi to PM to synthesis cellulose

Question 36

What drives the movement of cellulose?

Answer 36

Cellulose synthesis

Question 37

What is the process of cellulose deposition in the plant cell wall?

Answer 37

1. Cellulose fibrils synthesised and extruded through PM by cellulose synthase 2. Microtubules in cell determine orientation of deposition outside of cell