The Structure and Function of Large Biological Molecules

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Glucose

Fructose

Sucrose

Maltose

Glucose

Glucose

(a) Dehydration reaction in the synthesis of maltose

1–4

glycosidic

linkage

1–2

glycosidic

linkage

Slide 20

Polysaccharides

Polysaccharides, the polymers of sugars, have storage and structural roles

The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages

Slide 21

Storage Polysaccharides

Starch, a storage polysaccharide of plants, consists entirely of glucose monomers

Plants store surplus starch as granules within chloroplasts and other plastids

Slide 22

Fig. 5-6

(b) Glycogen: an animal polysaccharide

Starch

Glycogen

Amylose

Chloroplast

(a) Starch: a plant polysaccharide

Amylopectin

Mitochondria

Glycogen granules

0.5 µm

1 µm

Slide 23

Glycogen is a storage polysaccharide in animals

Humans and other vertebrates store glycogen mainly in liver and muscle cells

Slide 24

Structural Polysaccharides

The polysaccharide cellulose is a major component of the tough wall of plant cells

Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ

The difference is based on two ring forms for glucose: alpha () and beta ()

Animation: Polysaccharides

Slide 25

Fig. 5-7

(a)  and  glucose

ring structures

 Glucose

 Glucose

(b) Starch: 1–4 linkage of  glucose monomers

(b) Cellulose: 1–4 linkage of  glucose monomers

Slide 26

Fig. 5-7a

(a)  and  glucose ring structures

 Glucose

 Glucose

Slide 27

Fig. 5-7bc

(b) Starch: 1–4 linkage of  glucose monomers

(c) Cellulose: 1–4 linkage of  glucose monomers

Slide 28

Polymers with  glucose are helical

Polymers with  glucose are straight

In straight structures, H atoms on one strand can bond with OH groups on other strands

Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants