Plant Cell Walls

Question 1

What are cell walls derived from?`

Answer 1

Cell plates built at cytokinesis

Question 2

How much of the plant genome is dedicated to building cell walls?

Answer 2

10% of their genome, over ~3000 genes

Question 3

How much of the cell wall are polysaccharides?

Answer 3

90%

Question 4

Name 3 hemicelluloses?

Answer 4

Heteroxylans
Xyloglucans
Galactoglucomannans

Question 5

Name 2 pectins?

Answer 5

Rhamnogalacturonans

Xylogalacturonans

Question 6

What is the insoluble phase?

Answer 6

Tensile strength and rigidity

Question 7

What is the matrix?

Answer 7

Non-cellulosic glycans, pectins and phenollics

Question 8

How would you separate the 2 major classes of polysaccharides?

Answer 8

1. Pectins - calcium ion chelators

2. Hemicelluloses - Alkali

Question 9

What is lignin?

Answer 9

Not a polysaccharide - polyphenolic

Question 10

What are cellulose micofibrils made from?

Answer 10

Unbranched chains of B(1–>4) linked glycosyl residues

Question 11

What are the differences between CLGs and cellulose microfibrils?

Answer 11

1. CLGs cannto self-aggregate
2. CLGs can be solubilised with alkalis
3. Regions of CLGs hydrogen bond to the microfibrils forming cross-links

Question 12

What prevents aggregation in CLGs

Answer 12

Short side branches.

Question 13

What is in the CLG structure of dicots and grasses?

Answer 13

Dicots: Xyloglucans and lower levels of arabinoxylans
Grasses: Glucoronoarabinoxylans and lower levels of xyloglycans. Also mixed-linking glycans.

Question 14

What are the functions of hemicelluloses?

Answer 14

• Wall assembly
• Cross-linking microfibrils
• Cell expansion
• Cell wall mechanical properties and adhesion

Question 15

What is pectin??

Answer 15

GalA-rich polysaccharide

Question 16

What do PMEs do?

Answer 16

Pectin methylesterases removes methyl groups exposing carboxyl groups which can be cross-linked by Ca2+ resulting in gel formation

Question 17

What cross-links through RGII?

Answer 17

Borate diester