2 Chapter Outline 27.1 Carbohydrates: A First Class of Biochemicals 27.2 Classification of Carbohydrates 27.3 Importance of Carbohydrates 27.4 Monosaccharides 27.5 Structure of Glucose and Other Aldoses
3 Chapter Outline (continued) 27.6 Cyclic Structure of Glucose; Mutarotation 27.7 Hemiacetals and Acetals 27.8 Structures of Galactose and Fructose 27. 9 Pentoses 27.10 Disaccharides 27.11 Structures and Properties of Disaccharides 27.12 Sweeteners and Diet 27.13 Redox Reactions of Monosaccharides 27.14 Polysaccharides Derived from Glucose
7 A carbohydrate can be classified as: 1.monosaccharide 2.disaccharide 3.oligosaccharide 4.polysaccharide
8 Monosaccharides A monosaccharide is a carbohydrate that cannot be hydrolyzed to simpler carbohydrate units. The monosaccharide is the basic carbohydrate unit of cellular metabolism.
9 Disaccharides A disaccharide yields two monosaccharides – either alike or different – when hydrolyzed: disaccharide + water 2 monosaccharides H + or enzymes
10 Monosaccharides & Disaccharides Disaccharides are often used by plants or animals to transport monosaccharides from one cell to another. The monosaccharides and disaccharides generally have the ending –ose – for example, glucose, sucrose, and lactose. These are water-soluble carbohydrates, which have a characteristically sweet taste and are called sugars.
11 Oligosaccharides An oligosaccharide has two to six monosaccharide units linked together.
12 Polysaccharides A polysaccharide is a macromolecular substance that can be hydrolyzed to yield many monosaccharide units: polysaccharide + water monosaccharides H + or enzymes Polysaccharides are important structural supports, particularly in plants, and also serve as a storage depot for monosaccharides, which cells use for energy.
13 Other Ways to Classify Carbohydrates As a triose, tetrose, pentose, hexose, or heptose As an aldose or ketose As a D or L isomer As a (+) or (-) isomer As a furanose or a pyranose As having an alpha ( ) or beta ( ) configuration
15 Importance of Carbohydrates 1.Carbohydrates are very effective energy-yielding nutrients. 2.Carbohydrates can serve as very effective building materials. 3.Carbohydrates are important water- soluble molecules.
17 Monosaccharides The hexose monosaccharides are the most important carbohydrate sources of cellular energy. Three hexoses – glucose, galactose, and fructose – are of major significance in nutrition. –All three have the same formula, C 6 H 12 O 6, and thus deliver the same amount of cellular energy. –They differ in structure, but are biologically interconvertible.
18 Glucose (dextrose) is the most important of the monosaccharides. It is an aldohexose and is found in the free state in plant and animal tissue.
19 Galactose is also an aldohexose and occurs, along with glucose, in lactose and in many oligo- and polysaccharides such as pectin and gums.
20 Fructose, also know as levulose, is a ketohexose that occurs in fruit juices, honey, and along with glucose, as a constituent of sucrose.
29 Anomers When two cyclic isomers differ only in their stereo arrangement about the carbon involved in mutarotation, they are called anomers. Mutarotation is the process by which anomers are interconverted.
30 Figure 27. 4 Three-dimensional representations of the chair form of -D-glucopyranose
38 Disaccharides Disaccharides are carbohydrates composed of two monosaccharide residues united by a glycosidic linkage. sucrose + water glucose + fructose lactose + water galactose + glucose maltose + water glucose + glucose H+ or sucrase H+ or lactase H+ or maltase
48 Starch Starch is found in plants, mainly in the seeds, roots, or tubers. Corn, wheat potatoes, rice and cassava are the chief sources of dietary starch. The two main components of starch are amylose and amylopectin. –Amylose molecules are unbranched chains composed of about 25-1300 -D-glucose units joined by -1,4-glycosidic linkages.
52 Glycogen Glycogen is the energy-storage carbohydrate of the animal kingdom. It is formed by the polymerization of glucose and is stored in the liver and in muscle tissues. Structurally, it is very similar to the amylopectin fraction of starch, except that it is more highly branched. The -1,6-glycosidic linkages occur on one of every 12-18 glucose units.
53 Cellulose Cellulose is the most abundant organic substance found in nature. It is the chief structural component of plants and wood.
54 Figure 27.9 Two representations of cellulose. In the three- dimensional drawing, note the hydrogen bonding that links the extended cellulose polymers to form cellulose fibers.