885c07-238-27211/21/037:38 AM Page238Mac113mac11:4EDL chapter CARBOHYDRATES AND GLYCOBIOLOGY 7.1 Monosaccharides and disaccharides 239 attached to proteins or lipids act as signals that deter 7.2 Polysaccharides 247 mine the intracellular location or metabolic fate of these hybrid molecules, called glycoconjugates. This chap 7.3 Glycoconjugates: Proteoglycans, Glycoproteins, ter introduces the major classes of carbohydrates and glycoconjugates and provides a few examples of their 7.4 Carbohydrates as Informational Molecules: many structural and functional roles The Sugar Code 261 Carbohydrates are polyhydroxy aldehydes or ke- 7.5 Working with Carbohydrates 267 tones, or substances that yield such compounds on hy drolysis. Many, but not all, carbohydrates have the em- pirical formula (CHOni some also contain nitrogen, Ah! sweet mystery of life phosphorus, or sulfur. -Rida Johnson Young(lyrics)and Victor Herbert(music), There are three major size classes of carbohydrates Ah! Sweet Mystery of Life, 1910 monosaccharides, oligosaccharides, and polysaccha rides(the word"saccharide"is derived from the greek sakcharom, meaning"sugar). Monosaccharides, or I would feel more optimistic about a bright future for man simple sugars, consist of a single polyhydroxy aldehyde if he spent less time proving that he can outwit Nature or ketone unit. The most abundant monosaccharide in and more time tasting her sweetness and respecting her nature is the six-carbon sugar D-glucose, sometimes re- ferred to as dextrose. Monosaccharides of more than -E.B. White. "Coon Tree. "1977 four carbons tend to have cyclic structures Oligosaccharides consist of short chains of mono- saccharide units, or residues, joined by characteristic carbohydrates are the most abundant biomolecules linkages called glycosidic bonds. The most abundant are on Earth. Each year, photosynthesis converts more the disaccharides, with two monosaccharide units than 100 billion metric tons of COe and HO into cellu- Typical is sucrose(cane sugar), which consists of the lose and other plant products. Certain carbohydrates six-carbon sugars D-glucose and D-fructose. All common (sugar and starch) are a dietary staple in most parts of monosaccharides and disaccharides have names ending the world, and the oxidation of carbohydrates is the cen- with the suffix "-ose "In cells, most oligosaccharides tral energy-yielding pathway in most nonphotosynthetic consisting of three or more units do not occur as free cells. Insoluble carbohydrate polymers serve as struc- entities but are joined to nonsugar molecules (lipids or tural and protective elements in the cell walls of bacte- proteins) in glycoconjugates ria and plants and in the connective tissues of animals. The polysaccharides are sugar polymers contain- Other carbohydrate polymers lubricate skeletal joints ing more than 20 or so monosaccharide units, and some and participate in recognition and adhesion between have hundreds or thousands of units. Some polysac cells. More complex carbohydrate polymers covalently charides, such as cellulose, are linear chains; otherschapter Carbohydrates are the most abundant biomolecules on Earth. Each year, photosynthesis converts more than 100 billion metric tons of CO2 and H2O into cellu￾lose and other plant products. Certain carbohydrates (sugar and starch) are a dietary staple in most parts of the world, and the oxidation of carbohydrates is the cen￾tral energy-yielding pathway in most nonphotosynthetic cells. Insoluble carbohydrate polymers serve as struc￾tural and protective elements in the cell walls of bacte￾ria and plants and in the connective tissues of animals. Other carbohydrate polymers lubricate skeletal joints and participate in recognition and adhesion between cells. More complex carbohydrate polymers covalently attached to proteins or lipids act as signals that deter￾mine the intracellular location or metabolic fate of these hybrid molecules, called glycoconjugates. This chap￾ter introduces the major classes of carbohydrates and glycoconjugates and provides a few examples of their many structural and functional roles. Carbohydrates are polyhydroxy aldehydes or ke￾tones, or substances that yield such compounds on hy￾drolysis. Many, but not all, carbohydrates have the em￾pirical formula (CH2O)n; some also contain nitrogen, phosphorus, or sulfur. There are three major size classes of carbohydrates: monosaccharides, oligosaccharides, and polysaccha￾rides (the word “saccharide” is derived from the Greek sakcharon, meaning “sugar”). Monosaccharides, or simple sugars, consist of a single polyhydroxy aldehyde or ketone unit. The most abundant monosaccharide in nature is the six-carbon sugar D-glucose, sometimes re￾ferred to as dextrose. Monosaccharides of more than four carbons tend to have cyclic structures. Oligosaccharides consist of short chains of mono￾saccharide units, or residues, joined by characteristic linkages called glycosidic bonds. The most abundant are the disaccharides, with two monosaccharide units. Typical is sucrose (cane sugar), which consists of the six-carbon sugars D-glucose and D-fructose. All common monosaccharides and disaccharides have names ending with the suffix “-ose.” In cells, most oligosaccharides consisting of three or more units do not occur as free entities but are joined to nonsugar molecules (lipids or proteins) in glycoconjugates. The polysaccharides are sugar polymers contain￾ing more than 20 or so monosaccharide units, and some have hundreds or thousands of units. Some polysac￾charides, such as cellulose, are linear chains; others, CARBOHYDRATES AND GLYCOBIOLOGY 7.1 Monosaccharides and Disaccharides 239 7.2 Polysaccharides 247 7.3 Glycoconjugates: Proteoglycans, Glycoproteins, and Glycolipids 255 7.4 Carbohydrates as Informational Molecules: The Sugar Code 261 7.5 Working with Carbohydrates 267 Ah! sweet mystery of life . . . —Rida Johnson Young (lyrics) and Victor Herbert (music), “Ah! Sweet Mystery of Life,” 1910 I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit Nature and more time tasting her sweetness and respecting her seniority. —E. B. White, “Coon Tree,” 1977 7 238 8885d_c07_238-272 11/21/03 7:38 AM Page 238 Mac113 mac113:122_EDL: