Polysaccharides

Question 1

List the types of chemical bonds from strongest to weakest.

Answer 1

Covalent, metallic, ionic, hydrogen

Question 2

What is threshold strength for covalent bonds?

Answer 2

All covalent bonds have a bond strength of >100 kJ/mol

Question 3

What is the range of bond strength for secondary bonds?

Answer 3

1-10 kJ/mol

Question 4

Why does water act as a plasticizer?

Answer 4

It competes for H bonds

Question 5

What’s the energy of cellular adhesion?

Answer 5

10 kJ/mol

Question 6

What’s the binding energy of integrin-RGD (part of fibronectin)?

Answer 6

25 kJ/mol

Question 7

What is the basic structure of polysaccharides?

Answer 7

Linear chains of cyclic carbohydrates

Question 8

What side group makes polysaccharide structures very stable and why?

Answer 8

The side OH group because it makes it possible to form a lot of intermolecular and intramolecular H bonds

Question 9

What are the most abundant polysaccharides on earth and where are they found?

Answer 9

Cellulose (plants)

Chitin (insects)

Question 10

What are the characteristics of cellulose?

Answer 10

-Most abundant natural polymer on earth
-Basic building block for plants
-20-50% of the plant cell wall
-E=100 GPa, Strength = 1 GPa
-Most studied polysaccharide

Question 11

Which plant has the highest cellulose content?

Answer 11

Cotton (95%)

Question 12

What is the typical composition of wood?

Answer 12

40-55% linear cellulose
15-35% lignin
25-40% hemi cellulose (small, branched)

Question 13

What are the conditions required for polymer crystallization to occur?

Answer 13

-Polymer must be linear
-Polymer must have a regular chain structure

Question 14

How does the stiffness of semi-crystalline polymers compare to that of amorphous polymers?

Answer 14

Semi-crystalline polymers are 100 to 1000 time stiffer than amorphous polymers

Question 15

How does the crystallinity of cellulose fibrils affect their mechanical properties?

Answer 15

Cellulose fibrils are semi-crystalline

The crystals are oriented with the fiber which leads to high stiffness and high strength

Question 16

Describe the properties of cellulose nanofibrils

Answer 16

5-20 nm in diameter, 100s of nm long
E=145 GPa, Strength=7.5 GPa

Relatively cheap and biodegradable
Can be used in manmade composites

Question 17

What are two methods for orienting polymer crystals?

Answer 17

Drawing and stretching

Question 18

What is the effect of water on cellulose?

Answer 18

Water decreases the modulus of cellulose but it increases the strength and strain at failure

Question 19

Why is cellulose stronger than chitin?

Answer 19

Cellulose has the OH side chains but chitin doesn’t. This means that cellulose can be more closely packed and form hydrogen bonds

Question 20

What are the properties of chitin?

Answer 20

-Second most abundant natural polymer on earth
-E is on the order of GPas, strength is 60 to 200 MPa
-Very similar to cellulose but less studied
-Also capable of crystallizing

Question 21

What are the characteristics of hyaluronic acid?

Answer 21

A major component of synovial tissues and fluid, ECM, and other soft tissues
-High molecular weight
-Highly charged polymers
-Viscoelastic and rheological properties (lubricant/shock absorber)

Question 22

What characteristics has hyaluronic acid been linked with in naked mole rats?

Answer 22

-Tough and flexible skin
-Resistance to cancer
-Exceptional longevity

Question 23

Why are all proteins and polysaccharides sensitive to temperature and hydration?

Answer 23

The H bonds

Question 24

Do the stiffer and stronger proteins and polysaccharides tend to be amorphous or crystalline?

Answer 24

They tend to be more semi-crystalline

Question 25

Which proteins obey entropic elasticity?

Answer 25

The elastomeric proteins (elastin, resilin)