1. Carbon and the Molecular Diversity of Life3
Carbon and the Molecular Diversity of Life

2. Concept 3.2: Macromolecules are polymers, built from monomers
A polymer is a long molecule consisting of many similar building blocks
These small building-block molecules are called monomers
Some molecules that serve as monomers also have other functions of their own
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3. The Synthesis and Breakdown of Polymers
Cells make and break down polymers by the same mechanisms
A dehydration reaction occurs when two monomers bond together through the loss of a water molecule
Polymers are disassembled to monomers by hydrolysis, a reaction that is essentially the reverse of the dehydration reaction
These processes are facilitated by enzymes, which speed up chemical reactions
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4. Animation: Polymers
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5. (a) Dehydration reaction: synthesizing a polymer
Figure 3.7
(a) Dehydration reaction: synthesizing a polymer 1 2 3
Short polymer
Unlinked monomer 1 2 3 4
Longer polymer
(b) Hydrolysis: breaking down a polymer
Figure 3.7 The synthesis and breakdown of polymers 1 2 3 4 1 2 3
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6. (a) Dehydration reaction: synthesizing a polymer
Figure 3.7-1
(a) Dehydration reaction: synthesizing a polymer 1 2 3
Short polymer
Unlinked monomer
Figure The synthesis and breakdown of polymers (part 1: dehydration) 1 2 3 4
Longer polymer
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7. (b) Hydrolysis: breaking down a polymer
Figure 3.7-2
(b) Hydrolysis: breaking down a polymer 1 2 3 4
Figure The synthesis and breakdown of polymers (part 2: hydrolysis) 1 2 3
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8. The Diversity of Polymers
Each cell has thousands of different macromolecules
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
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9. Concept 3.3: Carbohydrates serve as fuel and building material
Carbohydrates include sugars and the polymers of sugars
The simplest carbohydrates are monosaccharides, or simple sugars
Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks
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10. Sugars
Monosaccharides have molecular formulas that are usually multiples of CH2O
Glucose (C6H12O6) is the most common monosaccharide
Monosaccharides are classified by the number of carbons in the carbon skeleton and the placement of the carbonyl group
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11. product of glucose in cells
Figure 3.8
Triose: three-carbon sugar (C3H6O3)
Pentose: five-carbon sugar (C5H10O5)
Glyceraldehyde
An initial breakdown
product of glucose in cells
Ribose
A component of RNA
Hexoses: six-carbon sugars (C6H12O6)
Figure 3.8 Examples of monosaccharides
Glucose
Fructose
Energy sources for organisms
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12. product of glucose in cells
Figure 3.8-1
Triose: three-carbon sugar (C3H6O3)
Figure Examples of monosaccharides (part 1: triose)
Glyceraldehyde
An initial breakdown
product of glucose in cells
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13. Pentose: five-carbon sugar (C5H10O5)
Figure 3.8-2
Pentose: five-carbon sugar (C5H10O5)
Figure Examples of monosaccharides (part 2: pentose)
Ribose
A component of RNA
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14. Hexoses: six-carbon sugars (C6H12O6)
Figure 3.8-3
Hexoses: six-carbon sugars (C6H12O6)
Figure Examples of monosaccharides (part 3: hexoses)
Glucose
Fructose
Energy sources for organisms
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15. Though often drawn as linear skeletons, in aqueous solutions many sugars form rings
Monosaccharides serve as a major nutrients for cells and as raw material for building molecules
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16. (a) Linear and ring forms
Figure 3.9
(a) Linear and ring forms
Figure 3.9 Linear and ring forms of glucose
(b) Abbreviated ring structure
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17. This covalent bond is called a glycosidic linkage
A disaccharide is formed when a dehydration reaction joins two monosaccharides
This covalent bond is called a glycosidic linkage
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18. Animation: Disaccharides
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19. Glucose Fructose Figure 3.10-s1
Figure 3.10-s1 Disaccharide synthesis (step 1)
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20. Glucose Fructose 1– 2 glycosidic linkage Sucrose Figure 3.10-s2
Figure 3.10-s2 Disaccharide synthesis (step 2)
Sucrose
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21. 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
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22. Storage Polysaccharides
Starch, a storage polysaccharide of plants, consists entirely of glucose monomers
Plants store surplus starch as granules
Most animals have enzymes that can hydrolyze plant start, making glucose available as a nutrient
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23. Glycogen is a storage polysaccharide in animals
Humans and other vertebrates store glycogen mainly in liver and muscle cells
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24. Animation: Polysaccharides
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25. Cellulose microfibrils in a plant cell wall
Figure 3.11
Storage structures
(plastids)
containing starch
granules in a potato
tuber cell
Amylose (unbranched)
Amylopectin
(somewhat
branched)
Glucose
monomer
50 mm
(a) Starch
Muscle
tissue
Glycogen
granules
in muscle
tissue
Glycogen
(extensively
branched)
Cell
wall
1 mm
Figure 3.11 Polysaccharides of plants and animals
(b) Glycogen
Cellulose microfibrils
in a plant cell wall
Cellulose molecule (unbranched)
Plant cell,
surrounded
by cell wall
10 mm
Microfibril
Hydrogen bonds
0.5 mm
(c) Cellulose
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26. Storage structures (plastids) containing starch granules in a potato
Figure
Storage structures
(plastids)
containing starch
granules in a potato
tuber cell
Amylose (unbranched)
Amylopectin
(somewhat
branched)
Glucose
monomer
50 mm
Figure Polysaccharides of plants and animals (part 1: starch)
(a) Starch
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27. Storage structures (plastids) containing starch granules in a potato
Figure a
Storage structures
(plastids)
containing starch
granules in a potato
tuber cell
Figure a Polysaccharides of plants and animals (part 1a: plastids containing starch granules, micrograph)
50 mm
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28. Glycogen granules in muscle Glycogen tissue (extensively branched)
Figure
Glycogen
granules
in muscle
tissue
Glycogen
(extensively
branched)
1 mm
(b) Glycogen
Figure Polysaccharides of plants and animals (part 2: glycogen)
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29. Glycogen granules in muscle tissue 1 mm Figure 3.11-2a
Figure a Polysaccharides of plants and animals (part 2a: glycogen granules, micrograph)
1 mm
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30. Cellulose microfibrils in a plant cell wall Cellulose molecule
Figure
Cellulose microfibrils
in a plant cell wall
Cellulose molecule
(unbranched)
Microfibril
Hydrogen bonds
0.5 mm
(c) Cellulose
Figure Polysaccharides of plants and animals (part 3: cellulose)
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31. Cell wall Plant cell, surrounded 10 mm by cell wall Figure 3.11-3a
Figure a Polysaccharides of plants and animals (part 3a: plant cell wall, micrograph)
10 mm
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32. Cellulose microfibrils in a plant cell wall
Figure b
Cellulose microfibrils
in a plant cell wall
Figure b Polysaccharides of plants and animals (part 3b: cellulose microfibrils, micrograph)
0.5 mm
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33. Structural Polysaccharides
The polysaccharide cellulose is a major component of the tough wall of plant cells
Like starch and glycogen, cellulose is a polymer of glucose, but the glycosidic linkages in cellulose differ
The difference is based on two ring forms for glucose
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34. (a)  and b glucose ring structures
Figure 3.12
(a)  and b glucose ring structures
 Glucose
b Glucose
Figure 3.12 Starch and cellulose structures
(b) Starch: 1–4 linkage of  glucose monomers
(c) Cellulose: 1–4 linkage of b glucose monomers
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35.  Glucose b Glucose (a)  and b glucose ring structures Figure 3.12-1
Figure Starch and cellulose structures (part 1: ring structures)
 Glucose
b Glucose
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36. (b) Starch: 1–4 linkage of  glucose monomers
Figure
Figure Starch and cellulose structures (part 2: starch linkage)
(b) Starch: 1–4 linkage of  glucose monomers
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37. (c) Cellulose: 1–4 linkage of b glucose monomers
Figure
Figure Starch and cellulose structures (part 3: cellulose linkage)
(c) Cellulose: 1–4 linkage of b glucose monomers
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38. Starch (and glycogen) are largely helical
In starch, the glucose monomers are arranged in the alpha () conformation
Starch (and glycogen) are largely helical
In cellulose, the monomers are arranged in the beta () conformation
Cellulose molecules are relatively straight
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39. In cellulose, some hydroxyl groups on its glucose monomers can hydrogen-bond with hydroxyl groups of other cellulose molecules
Parallel cellulose molecules held together this way are grouped into microfibrils, which form strong building materials for plants
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40. Some microbes use enzymes to digest cellulose
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
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41. Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods
Chitin also provides structural support for the cell walls of many fungi
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