Chemistry
Classification of Carbohydrates
Carbohydrates are classified based on their structure and the number of sugar units they contain. Monosaccharides are the simplest carbohydrates, consisting of a single sugar unit. Disaccharides are composed of two sugar units, while polysaccharides are made up of multiple sugar units. Carbohydrates are also categorized as simple or complex based on their chemical structure and how quickly they are digested.
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10 Key excerpts on "Classification of Carbohydrates"
- Frederick Bettelheim, William Brown, Mary Campbell, Shawn Farrell(Authors)
- 2019(Publication Date)
- Cengage Learning EMEA(Publisher)
525 CONTENTS 19.1 Monosaccharides: The Simplest Carbohydrates 19.2 Cyclic Structures of Monosaccharides 19.3 Characteristic Reactions of Monosaccharides 19.4 Disaccharides and Oligosaccharides 19.5 Polysaccharides 19.6 Acidic Polysaccharides Carbohydrates 19 19.1 Monosaccharides: The Simplest Carbohydrates Carbohydrates are the most abundant organic compounds in the plant world. They provide chemical energy (glucose, starch, glycogen); are com-ponents of supportive structures in plants (cellulose), crustacean shells (chitin), and connective tissues in animals (acidic polysaccharides); and are essential components of nucleic acids ( D -ribose and 2-deoxy-D -ribose). Carbohydrates account for approximately three-fourths of the dry weight of plants. Animals (including humans) get their carbohydrates by eating plants, but they do not store much of what they consume. In fact, less than 1% of the body weight of animals is made up of carbohydrates. Carbohydrate means “hydrate of carbon” and derives from the formula C n s H 2 O d m , such as: ● Glucose (blood sugar): C 6 H 12 O 6 , which can be written as C 6 s H 2 O d 6 ● Sucrose (table sugar): C 12 H 22 O 11 , which can be written as C 12 s H 2 O d 11 Not all carbohydrates have this general formula, but the term carbohydrate has become so firmly rooted in the chemical nomenclature that, although not completely accurate, it persists as the name for this class of compounds. At the molecular level, most carbohydrates are polyhydroxyalde-hydes, polyhydroxyketones, or compounds that yield them after hydrolysis. The simpler members of the carbohydrate family are often referred to as saccharides because of their sweet taste (Latin: saccharum, “sugar”). Car-bohydrates are classified as monosaccharides, oligosaccharides, or polysac-charides depending on the number of simple sugars they contain. Carbohydrates Polyhydroxyaldehydes or polyhydroxyketones, or substances that give these compounds on hydrolysis Charles D.
eBook - PDF- BIOTOL, B C Currell, R C E Dam-Mieras(Authors)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
127 Carbohydrates 5.1 Classes of carbohydrates 128 5.2 Monosaccharides 129 5.3 Isomerism in monosaccharides 130 5.4 Properties of monosaccharides 138 5.5 Disaccharides 140 5.6 Polysaccharides 142 Summary and objectives 150 128 Chapter 5 roles of Carbohydrates We have already referred to the fact that cells are made of a restricted number of major classes of molecules. As we have progressed through the examination of these classes of molecules we have commented that, in all aspects of cell function, there seems to be a close relationship between the structure of a molecule and its biological function. In this and the next chapter, we discuss carbohydrates and lipids. Unlike proteins and nucleic acids, neither of these classes of molecules possess information within their carbohydrates structures (as the amino acid sequence of a protein or the base sequence of a nucleic acid and lipids does). Carbohydrates and lipids tend to have less precise structures than proteins and nucleic acids. This is presumably because their roles within cells can be adequately fulfilled without precisely controlled (or uniform) structures. They none-the-less have vital roles, as follows: Carbohydrates • Biological fuel • Storage form of food reserves • Structural components of cell walls Lipids • Fuels and storage forms of fuel • Major components of cell membranes We shall return to these functions later in this and the next chapter. For the major part of this chapter, we will examine the structure and properties of carbohydrates. 5.1 Classes of carbohydrates Carbohydrates are conveniently subdivided into three groups: Monosaccharides These consist of single 'units' and are important in metabolism and as the building blocks from which the remaining three groups are constructed. Disaccharides glycosidic bond These consist of two monosaccharides linked through a glycosidic bond. Oligosaccharides contain a few (3-6) monosaccharide units linked by glycosidic bonds.
eBook - PDF- Allan Blackman, Steven E. Bottle, Siegbert Schmid, Mauro Mocerino, Uta Wille(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
CHAPTER 22 Carbohydrates LEARNING OBJECTIVES After studying this chapter, you should be able to: 22.1 define carbohydrates 22.2 describe monosaccharides using aldose/ketose terminology 22.3 understand and describe the cyclic structure of monosaccharides 22.4 describe the chemical reactions of monosaccharides 22.5 explain disaccharides and oligosaccharides 22.6 define polysaccharides and describe starch, glycogen and cellulose. Carbohydrates is probably the chemical term that is most widely used by the general public. Commonly referred to as ‘carbs’, it seems everyone has an idea of how much, or how little, or what type we should be consuming in our diets. Carbohydrates are in fact a major class of organic molecules that are important not only in food, but more broadly in biochemistry, medicines, agriculture and even as structural materials. Carbohydrates act as storehouses of chemical energy (glucose, starch, glycogen) and are components of supportive structures in plants (cellulose), crustacean shells (chitin) and connective tissues in animals (polysaccharides). Carbohydrates are also essential components in the nucleic acids RNA(d-ribose) and DNA (2-deoxy- d-ribose), and they play crucial roles in cell surface and membrane recognition that are necessary for cell function. Small carbohydrate molecules, such as glucose, are readily soluble in water and so can be transported through the vascular system to meet a plant’s or animal’s energy requirements. Chemists are increasingly interested in carbohydrates as a potential solution for many of the problems caused by the burning of fossil fuels for energy. Increasing research efforts are being focused on ‘biofuels’, largely ethanol, derived from cellulose. Cellulose accounts for approximately three-quarters of the dry weight of the plant, where it is used to provide plant cell walls with strength and rigidity.
eBook - PDF- Jose Perez-Castineira(Author)
- 2020(Publication Date)
- De Gruyter(Publisher)
3 Carbohydrates 3.1 Definition, terminology, and classification Carbohydrates are a family of biomolecules composed, in principle, by carbon (C), hydrogen (H), and oxygen (O) atoms whose basic general formula is C n (H 2 O) m . The fact that many carbohydrates have two atoms of hydrogen per atom of oxygen in their molecules is responsible for the somewhat misleading name that these mole- cules have, as “hydrate” means “containing water.” Carbohydrates have no water in their chemical composition, as we shall see in this Chapter, although they are usually hydrated to different degrees both in vivo and in vitro. Carbohydrates are usually constituted by an indeterminate number of basic units linked forming polymers. The connections among these units may occur by means of different linkage types, thereby allowing many structural variations [1]. There are several important terms related to carbohydrates: – Monosaccharides: They are the basic non-hydrolyzable units of carbohydrates. Monosaccharides can be chemically altered yielding derivatives that may also form polymers. These alterations may involve the addition of elements such as nitrogen (N), sulfur (S), or phosphorus (P). – Oligosaccharides. Molecules composed of 2 to 12 (20 for some authors) linked units (residues) of monosaccharides by a specific type of chemical bond known as glycosidic bond. Oligosaccharides are denoted according to the number of monosaccharide residues they have: disaccharides (2 units), trisaccharides (3), tetrasaccharides (4), and so on. – Sugar: Many monosaccharides and disaccharides are sweet, hence their trivial name sugars, although table sugar is only composed of sucrose, a disaccha- ride. Carbohydrates are also known as glycids (from the Greek glykys, glykeros: sweet) or saccharides (from the latin saccharum: sugar). – Polysaccharides: Polymers composed of more than 12 (or 20) residues of mono- saccharides.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
Grafissimo/iStockphoto 27.1 Carbohydrates: A First Class of Biochemicals 27.2 Classification of Carbohydrates 27.3 Importance of Carbohydrates for Life 27.4 Common Monosaccharides 27.5 Structure of Glucose and Other Aldoses 27.6 Cyclic Structures of Common Hexoses 27.7 Hemiacetals and Acetals 27.8 Pentoses 27.9 Structures and Properties of Disaccharides 27.10 Sweeteners and Diet 27.11 Redox Reactions of Monosaccharides 27.12 Polysaccharides CARBOHYDRATES Bread is the staff of life because it is mainly carbohydrate. C H A P T E R O U T L I N E W hat is the most abundant organic chemical in the world? The answer is not petroleum products, plastics, or drugs. Rather, it is cellulose. An amazing 10 billion tons of cellulose are formed daily in the biosphere. Aggregates of cellulose allow the California redwoods to stretch hundreds of feet toward the sky and make a Brazil nut a “hard nut to crack.” Products as diverse as the paper in this book and cotton in clothing are derived from cellulose. So, perhaps it is not surprising that this carbohydrate is the most widespread organic chemical in the world. Carbohydrates are molecules of exceptional utility. They provide basic diets for many of us (starch and sugar), roofs over our heads, and clothes for our bodies (cellulose). They also thicken our ice cream, stick postage stamps to our letters, and provide biodegradable plastic trash sacks. From relatively simple components (carbon, hydrogen, and oxygen), nature has created one of the premier classes of biochemicals. C H A P T E R 27 27.1 • Carbohydrates: A First Class of Biochemicals 695 27.1 CARBOHYDRATES: A FIRST CLASS OF BIOCHEMICALS Describe the general characteristics of a carbohydrate. Carbohydrates are among the most widespread and important biochemicals. Most of the matter in plants, except water, consists of these substances. Carbohydrates are one of the three principal classes of energy-yielding nutrients; the other two are fats and proteins.
eBook - PDF- William H. Brown, Thomas Poon(Authors)
- 2017(Publication Date)
- Wiley(Publisher)
563 17 Carbohydrates K E Y Q U E S T I O N S 17.1 What Are Carbohydrates? 17.2 What Are Monosaccharides? 17.3 What Are the Cyclic Structures of Monosaccharides? 17.4 What Are the Characteristic Reactions of Monosaccharides? 17.5 What Are Disaccharides and Oligosaccharides? 17.6 What Are Polysaccharides? H O W TO 17.1 Determine the Stereochemistry of OH Groups in Cyclic D‐Monosaccharides 17.2 Determine If a Carbohydrate Is a Reducing Sugar C H E M I C A L C O N N E C T I O N S 17A Relative Sweetness of Carbohydrate and Artificial Sweeteners 17B A, B, AB, and O Blood‐Group Substances Charles D. Winters Breads, grains, and pasta are sources of carbohydrates. Inset: A model of glucose, the most abundant carbohydrate in nature. 17.1 What Are Carbohydrates? Carbohydrates are the most abundant organic compounds in the plant world. They act as storehouses of chemical energy (glucose, starch, glycogen); are components of supportive structures in plants (cellulose), crustacean shells (chitin), and connective tissues in animals (acidic polysaccharides); and are essential components of DNA and RNA (d‐ribose and 2‐deoxy‐d‐ribose). Carbohydrates account for approximately three‐fourths of the dry weight of plants. Animals (including humans) get their carbohydrates by eating plants, but they do not store much of what they consume. In fact, less than 1% of the body weight of animals is made up of carbohydrates. The word carbohydrate means “hydrate of carbon” and derives from the formula C n (H 2 O) m . Two examples of carbohydrates with molecular formulas that can be written alternatively as hydrates of carbon are ● glucose (blood sugar), C 6 H 12 O 6 , which can be written as C 6 (H 2 O) 6 , and ● sucrose (table sugar), C 12 H 22 O 11 , which can be written as C 12 (H 2 O) 11 . Not all carbohydrates, however, have this general formula. Some contain too few oxygen atoms to fit the formula, whereas some contain too many.
eBook - PDF- William H. Brown, Thomas Poon(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
563 17.1 What Are Carbohydrates? Carbohydrates are the most abundant organic compounds in the plant world. They act as storehouses of chemical energy (glucose, starch, glycogen); are components of supportive structures in plants (cellulose), crustacean shells (chitin), and connective tissues in animals (acidic polysaccharides); and are essential components of DNA and RNA (d‐ribose and 2‐deoxy‐d‐ribose). Carbohydrates account for approximately three‐fourths of the dry weight of plants. Animals (including humans) get their carbohydrates by eating plants, but they do not store much of what they consume. In fact, less than 1% of the body weight of animals is made up of carbohydrates. The word carbohydrate means “hydrate of carbon” and derives from the formula C n (H 2 O) m . Two examples of carbohydrates with molecular formulas that can be written alternatively as hydrates of carbon are ● glucose (blood sugar), C 6 H 12 O 6 , which can be written as C 6 (H 2 O) 6 , and ● sucrose (table sugar), C 12 H 22 O 11 , which can be written as C 12 (H 2 O) 11 . Not all carbohydrates, however, have this general formula. Some contain too few oxygen atoms to fit the formula, whereas some contain too many. Some also contain nitrogen. But 17. Carbohydrates K E Y Q U E S T I O N S 17.1 What Are Carbohydrates? 17.2 What Are Monosaccharides? 17.3 What Are the Cyclic Structures of Monosaccharides? 17.4 What Are the Characteristic Reactions of Monosaccharides? 17.5 What Are Disaccharides and Oligosaccharides? 17.6 What Are Polysaccharides? H O W TO 17.1 Determine the Stereochemistry of OH Groups in Cyclic D‐Monosaccharides 17.2 Determine If a Carbohydrate Is a Reducing Sugar C H E M I C A L C O N N E C T I O N S 17A Relative Sweetness of Carbohydrate and Artificial Sweeteners 17B A, B, AB, and O Blood‐Group Substances 17 Charles D. Winters Breads, grains, and pasta are sources of carbohydrates. Inset: A model of glucose, the most abundant carbohydrate in nature.
eBook - PDF- Robert E.C. Wildman, Denis M. Medeiros(Authors)
- 2014(Publication Date)
- CRC Press(Publisher)
Not only were they composed of only carbon, hydrogen and oxygen, but also the ratio of carbon to water is typically one to one (C:H20). Thus, carbohydrate literally means carbon with water. Chemical carbohydrates are defined as polyhydroxyl aldehydes and ketones and their derivatives. Carbohydrates can vary from simpler 3- to 7-carbon single unit molecules to very complex branching polymers. While hundreds of different carbohydrates exist in nature, this text will take the simplest approach and group them into just a few broad categories: monosaccharides , disaccharides , oligosaccharides , and polysaccharides. Monosaccharides The monosaccharides that are relevant to human nutrition may be classified based on car bon number and include the trioses, tetroses, pentoses, and hexoses. Both aldoses (alde hydes) and ketoses (ketones) are present (Figure 4.1). Hexoses are the more common form of monosaccharides in the human diet. These include glucose , galactose , and fructose. Glu cose is found in some foods in a free form, especially ripened fruits and vegetables, while the majority of the glucose in the human diet is derived from the digestion of disaccharides and starch. Glucose is also the principal carbohydrate found in human circulation and is often referred to as blood sugar. Galactose is also found free in some foods, but to a relatively small degree. Most of the galactose in the human diet is derived from the digestion of the disaccharide lactose, which is found in milk and dairy foods. Fructose is found naturally in fruits and honey and is also derived from the disaccharide sucrose. Fructose is also pro vided in the human diet in the form of the popular food sweetening agent high-fructose com syrup (HFCS). Trioses such as glyceraldehyde and dihydroxyacetone are found as intermediary prod ucts of metabolic pathways (i.e., glycolysis). Tetroses include erythrose, threose, and eryth- rulose.
eBook - PDF- David Ucko(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
ar drates Carbohydrates are one of your major sources of energy. They are synthesized by plants in a process called photosynthesis. Plants use the energy of sunlight to convert carbon dioxide, a waste product of your body, along with water into carbohydrate molecules. Carbohydrates serve as an important f u e l in humans because energy from the sun is stored in their chemical bonds. It is released w h e n carbohydrates are b u r n e d in your body. T o follow this process (which is described in detail in Chapter 17), you must understand the structures and properties of the most important carbohydrate molecules. ass at n ar drates Carbohydrates are organic molecules that contain carbon, hydrogen, and oxy-gen. At one time, it was thought that they were hydrates of carbon—there-fore, the name carbohydrate. Although many carbohydrate molecules do have the ratio o f two hydrogen atoms to one oxygen atom (as in H 2 0 ) for every carbon atom, this definition is not correct. Carbohydrates are related to either aldehydes or ketones and also contain hydroxyl groups. Thus, they can b e d e -fined as polyhydroxyl aldehydes or polyhydroxyl ketones ( p o l y means many) or as substances that produce these compounds upon hydrolysis (when they react with water) and their derivatives. Carbohydrates are classified according to their size. T h e largest carbohy-drates are polymers called polysaccharides; they contain many monomers linked together. These basic units, the simplest carbohydrates, are called monosaccharides. Polysaccharides can b e hydrolyzed, broken d o w n in a reac-tion with water (in the presence of acid) to produce monosaccharides. T h e monosaccharides, however, cannot b e changed to simpler molecules. In between the large polysaccharides and the single monosaccharides are the oligosaccharides. T h e y contain a small number of monosaccharide units, gen-erally from two to ten, b o n d e d together. T h e most important oligosaccharides 296
eBook - PDFSweeteners
Nutritional Aspects, Applications, and Production Technology
- Theodoros Varzakas, Athanasios Labropoulos, Stylianos Anestis(Authors)
- 2012(Publication Date)
- CRC Press(Publisher)
2.5 POLYSACCHARIDES Polysaccharides are very important for human nutrition and widely distributed in nature. It is estimated that more than 90% of the considerable carbohydrate mass in nature is in the form of poly-saccharides. Examples include storage polysaccharides, such as starch and glycogen, and structural polysaccharides, such as cellulose and chitin. Polysaccharides (glycans) are high molecular weight polymers of monosaccharides and are named after their component monosaccharide. The degree of polymerization (DP), which is determined by the number of monosaccharide units in a chain, varies from a hundred to a few hundred thousand. Polysaccharides can be either linear or branched. Based on the number of different monomers present, polysaccharides can be divided into homopolysac-charides, consisting of only one kind of monosaccharide (e.g., cellulose and starch amylose, which are linear and starch amylopectin, which is branched), and heteropolysaccharides, consisting of two or more kinds of monosaccharide units (e.g., hemicellulose and pectins). Hydrolysis of glycosidic bonds joining monosaccharide (glycosyl) units in polysaccharides can be catalyzed by either acids or enzymes (BeMiller and Whistler 1996; Belitz et al. 2009). Although it seems macroscopically and microscopically amorphous, X-ray analysis has revealed polysaccharides’ microcrystalline structure. Depending on the structure, polysaccharides may have distinct properties from their monosaccharide building blocks. Thus, they do not have sweet taste, they do not reduce Fehling’s solution, and they differ in solubility—they may be easily soluble (glycogen) or form colloidal solutions in water (starch) or are insoluble in warm water (cellulose). 2.5.1 Homopolysaccharides The major homopolysaccharides are starch, cellulose, and glycogen. 2.5.1.1 Starch Among food carbohydrates, starch occupies a unique position.
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