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Unformatted text preview: Chapter 5: The Molecules of Life • All living things are made up of four classes of large biological molecules: carbohydrates, lipids, proteins, and nucleic acids • Within cells, small organic molecules are joined together to form larger molecules • Macromolecules are large molecules composed of thousands of covalently connected atoms • Molecular structure and function are inseparable • Concept 5.1: 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 • Three of the four classes of life’s organic molecules are polymers: – Carbohydrates – Proteins – Nucleic acids • The Synthesis and Breakdown of Polymers • A condensation reaction or more specifically a dehydration reaction occurs when two monomers bond together through the loss of a water molecule • Enzymes are macromolecules that speed up the dehydration process • Polymers are disassembled to monomers by hydrolysis , a reaction that is essentially the reverse of the dehydration reaction Figure 5.2 The synthesis and breakdown of polymers • 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 • Sugars • Monosaccharides have molecular formulas that are usually multiples of CH 2 O • Glucose (C 6 H 12 O 6 ) 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 Figure 5.3 The structure and classification of some monosaccharides Figure 5.4 Linear and ring forms of glucose • A disaccharide is formed when a dehydration reaction joins two monosaccharides • This covalent bond is called a glycosidic linkage Figure 5.5 Examples of disaccharide synthesis • 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 • Storage Polysaccharides • Starch , a storage polysaccharide of plants, consists entirely of glucose monomers • Plants store surplus starch as granules within chloroplasts and other plastids Figure 5.6 Storage polysaccharides of plants and animals • Glycogen is a storage polysaccharide in animals • Humans and other vertebrates store glycogen mainly in liver and muscle cells • 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 ( α ) and beta ( β ) Figure 5.7 Starch and cellulose structuresFigure 5....
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