The Structure and Function of Large Biological Molecules

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Macromolecules vary among cells of an organism, vary more within a species, and vary even more between species

An immense variety of polymers can be built from a small set of monomers

2

3

HO

H

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Concept 5.2: Carbohydrates serve as fuel and building material

Carbohydrates include sugars and the polymers of sugars

The simplest carbohydrates are monosaccharides, or single sugars

Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks

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Sugars

Monosaccharides have molecular formulas that are usually multiples of CH2O

Glucose (C6H12O6) is the most common monosaccharide

Monosaccharides are classified by

The location of the carbonyl group (as aldose or ketose)

The number of carbons in the carbon skeleton

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Fig. 5-3

Dihydroxyacetone

Ribulose

Ketoses

Aldoses

Fructose

Glyceraldehyde

Ribose

Glucose

Galactose

Hexoses (C6H12O6)

Pentoses (C5H10O5)

Trioses (C3H6O3)

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Fig. 5-3a

Aldoses

Glyceraldehyde

Ribose

Glucose

Galactose

Hexoses (C6H12O6)

Pentoses (C5H10O5)

Trioses (C3H6O3)

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Fig. 5-3b

Ketoses

Dihydroxyacetone

Ribulose

Fructose

Hexoses (C6H12O6)

Pentoses (C5H10O5)

Trioses (C3H6O3)

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Though often drawn as linear skeletons, in aqueous solutions many sugars form rings

Monosaccharides serve as a major fuel for cells and as raw material for building molecules

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Fig. 5-4

(a) Linear and ring forms

(b) Abbreviated ring structure

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Fig. 5-4a

(a) Linear and ring forms

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Fig. 5-4b

(b) Abbreviated ring structure

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A disaccharide is formed when a dehydration reaction joins two monosaccharides

This covalent bond is called a glycosidic linkage

Animation: Disaccharides

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Fig. 5-5

(b) Dehydration reaction in the synthesis of sucrose