The Structure and Function of Large Biological Molecules

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Slide 29

Fig. 5-8

Glucose

monomer

Cellulose

molecules

Microfibril

Cellulose

microfibrils

in a plant

cell wall

0.5 µm

10 µm

Cell walls

Slide 30

Enzymes that digest starch by hydrolyzing  linkages can’t hydrolyze  linkages in cellulose

Cellulose in human food passes through the digestive tract as insoluble fiber

Some microbes use enzymes to digest cellulose

Many herbivores, from cows to termites, have symbiotic relationships with these microbes

Slide 31

Fig. 5-9

Slide 32

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods

Chitin also provides structural support for the cell walls of many fungi

Slide 33

Fig. 5-10

The structure

of the chitin

monomer.

(a)

(b)

(c)

Chitin forms the

exoskeleton of

arthropods.

Chitin is used to make

a strong and flexible

surgical thread.

Slide 34

Concept 5.3: Lipids are a diverse group of hydrophobic molecules

Lipids are the one class of large biological molecules that do not form polymers

The unifying feature of lipids is having little or no affinity for water

Lipids are hydrophobic becausethey consist mostly of hydrocarbons, which form nonpolar covalent bonds

The most biologically important lipids are fats, phospholipids, and steroids

Slide 35

Fats

Fats are constructed from two types of smaller molecules: glycerol and fatty acids

Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon

A fatty acid consists of a carboxyl group attached to a long carbon skeleton

Slide 36

Fig. 5-11

Fatty acid

(palmitic acid)

Glycerol

(a) Dehydration reaction in the synthesis of a fat

Ester linkage

(b) Fat molecule (triacylglycerol)

Slide 37

Fig. 5-11a

Fatty acid

(palmitic acid)

(a)

Dehydration reaction in the synthesis of a fat

Glycerol

Slide 38

Fig. 5-11b

(b)

Fat molecule (triacylglycerol)

Ester linkage