Biological Sciences
Monosaccharides
Monosaccharides are the simplest form of carbohydrates, consisting of a single sugar molecule. They are the building blocks of more complex carbohydrates and are essential for energy production in living organisms. Common examples of monosaccharides include glucose, fructose, and galactose.
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12 Key excerpts on "Monosaccharides"
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 - PDFBiochemistry
An Integrative Approach
- John T. Tansey(Author)
- 2019(Publication Date)
- Wiley(Publisher)
Likewise, reactions that have ΔG° values close to zero can be tipped to move in either direction by changing the concentrations of substrates or products. • The synthesis of glucose and the degradation of Monosaccharides use similar reactions but different pathways. Key steps are different, and compartmentalization is important. A similar theme is seen in fatty acid metabolism. DYNAMIC FIGURE 6.1 Carbohydrates can be simply classified as Monosaccharides (single building blocks) or polysaccharides (polymers of Monosaccharides). Polysaccharides can serve structural roles or can serve as a stored form of energy. Monosaccharides can be catabolized into pyruvate. Likewise, pyruvate can be used to synthesize new glucose through gluconeogenesis. 6.1 Properties, Nomenclature, and Biological Functions of Monosaccharides 163 6.1 Properties, Nomenclature, and Biological Functions of Monosaccharides Carbohydrates are a group of biological molecules with the basic formula C x (H 2 O) x , hence the name “carbo-hydrate.” At their most basic level, carbohydrates have the equivalent of one molecule of water for every carbon atom. This means that carbohydrates are polyhydroxy aldehydes or polyhydroxy ketones, that is, molecules in which one carbon bears a carbonyl group (CO) and the others all carry hydroxyls (OH). They also contain at least three carbons. We will first discuss the basic structures of carbohydrates and different ways we can represent these molecules on paper, and then we will move into modifications of these molecules. H C OH H C OH H C OH C CH 2 OH CH 2 OH O Generic formula Bond-angle depiction of a carbohydrate Fischer projection of a carbohydrate C x (H 2 O) x Formula of a carbohydrate C 6 H 12 O 6 O OH OH OH OH OH 6.1.1 Monosaccharides are the simplest carbohydrates This section focuses on the simplest carbohydrates, the Monosaccharides. Monosaccharides can be linked together to form more complex carbohydrates.
eBook - PDF- David Ucko(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
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 13.2 / n sa ar des 297 monosaccharide ~~— I disaccharide polysaccharide u re ar de e resentat ns a n sa ar de d sa ar de and sa are the disaccharides, which consist of two Monosaccharides joined by a chemical bond. These definitions are illustrated in Figure 13-1. T h e term sugar generally applies only to those Monosaccharides and oligosaccharides that are soluble in water and taste sweet. n sa ar des Monosaccharides are further classified according to their functional group. Those based on an aldehyde group are called aldoses, while those containing a ketone group are ketoses. T h e ending -o s e is characteristic of the simple carbohydrates. T h e Monosaccharides are also divided into groups on the basis of the number of carbon atoms in the molecule. A triose, a three-carbon monosac-charide, is the smallest possible carbohydrate. A tetrose contains four carbon atoms, and a pentose has five. T h e hexoses, molecules with six carbon atoms, are the most important group of Monosaccharides. These two systems of classification can b e combined. For example, a five-carbon monosaccharide with a ketone group is called a ketopentose. Simi-larly, an aldose with six carbon atoms is an aldohexose. Glyceraldehyde, the simplest of all Monosaccharides, is an aldotriose, Ο C H H — C — O H C H 2 O H glyceraldehyde formed from the breakdown o f hexoses in muscle tissue. It contains three carbon atoms, one of w h i c h forms part of an aldehyde group. Each of the other two carbon atoms is b o n d e d to a hydroxyl group. You can think of larger m o n o - a ter ar drates saccharides (that are aldoses) as derived from glyceraldehyde b y lengthening the chain o f carbon atoms.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
A polysaccharide is a macromolecular substance that can be hydrolyzed to yield many monosaccharide units: polysaccharide + water 9999: H + or enzymes many monosaccharide units Polysaccharides are important as structural supports, particularly in plants, and also serve as a storage depot for Monosaccharides, which cells use for energy. Carbohydrates are vital to life, so it is not surprising that they have also been classified with respect to their impact on metabolism. Originally, mono- and disaccharides were grouped together as the simple sugars—carbohydrates that were easily digested and that produced a rapid increase in blood sugar after a meal. The oligo- and polysaccharides were placed in the complex carbohydrate category—carbohydrates that would release glucose more slowly dur- ing digestion. More research has shown that dietary carbohydrates’ effect on blood glucose is more complex than these categories suggest. Today’s nutritionists rank carbohydrates via the glycemic index. This is an experimental measure of a carbohydrate’s impact on blood sugar relative to a standard, either glucose or white bread. It has been shown that a diet of carbohydrates with a higher glycemic index correlates with greater risk of diabetes (Type 2) and coronary heart disease. That is, if a carbohydrate has a low glycemic index, it is probably a healthier food. Carbohydrates can also be classified in other ways. A monosaccharide might be described with respect to several of these categories: 1. As a triose, tetrose, pentose, hexose, or heptose: Trioses C 3 H 6 O 3 Hexoses C 6 H 12 O 6 Tetroses C 4 H 8 O 4 Heptoses C 7 H 14 O 7 Pentoses C 5 H 10 O 5 Theoretically, a monosaccharide can have any number of carbons greater than three, but only Monosaccharides of three to seven carbons are commonly found in the biosphere. 2. As an aldose or ketose, depending on whether an aldehyde group ( i CHO) or keto group ( C O) is present. For ketoses, the C O is normally located on carbon 2.
- 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- Sharma, Dipiti(Authors)
- 2021(Publication Date)
- Daya Publishing House(Publisher)
4 Carbohydrates 4.0 Introduction The most abundant organic molecules in nature. Plant use CO 2 and Water and energy (from Sun) to Produce CHO. These are organic compounds that contain CARBON, HYDROGEN, and OXYGEN in the ratio of 1 :2: 1.The general formula is (CH 2 O)n. They provide a significant fraction of the energy in the diet of most organisms and are important source of energy for cells. Carbohydrates are Polyhydroxy aldehydes or ketones, or substances that yield these compounds on hydrolysis. Carbohydrates performs following functions: Can act as a storage form of energy Can be structural components of many organisms Can be cell-membrane components mediating intercellular communication Can be cell-surface antigens Can be part of the body’s extracellular ground substance Can be associated with proteins and lipids Is part of RNA, DNA, and several coenzymes (NAD + , NADP + , FAD, CoA). 4.1 Carbohydrate Classification and Structure This ebook is exclusively for this university only. Cannot be resold/distributed. There are two main classes of carbohydrates: SIMPLE (sugars) and COMPLEX (starches and fiber) carbohydrates. Simple Sugars (sugar is also known as Saccharide) are the building blocks of complex sugars and polysaccharides. Simple sugars are further classified as: Figure 4.1: Photosynthesis: Sun’s Energy becomes Part of Glucose Molecule. Monosaccharides DIsaccharides P Glucose (principal monosaccharide in the body), P Sucrose= Glucose+ Fructose P Fructose P Lactose= Glucose + Galactose P Galactose P Maltose= Glucose + Glucose 4.1.1 Simple Sugar This ebook is exclusively for this university only. Cannot be resold/distributed. 4.1.1.1. Monosaccharides These are simple sugars containing short chains of carbon atoms with one aldehydic or ketonic group (carbonyl group), each of remaining carbons bear a hydroxyl group. Polyhydroxy aldehydes or ketones that can’t easily be further hydrolyzed are “Simple sugars”.
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.
eBook - PDF- P Karlson(Author)
- 1975(Publication Date)
- Academic Press(Publisher)
C H A P T E R Simple Sugars, Monosaccharides The simple sugars constitute a subclass of the great class of natural substances, the carbohydrates. In sheer amount, the carbohydrates make up the bulk of organic substance on this earth. Though predominantly of plant origin, they constitute the principal component of the food of many animals and of man. Of the customary divisions of foodstuffs—protein, fats, and carbohydrates—the carbohydrates rank highest as energy suppliers. Many simple sugars contain carbon and the elements of water in the ratio of 1:1 ; this fact has caused the name carbohydrate to be given to this class of compounds. T h e designation originated at a time w h e n real significance was attached to the empirical f o r m u l a C x ( H 2 0 ) „ , w h i c h represents these substances as hydrates of the element carbon. T o d a y w e are n o longer b o u n d b y the empirical f o r m u l a ; w e call d e o x y r i b o s e C 5 H 1 0 O 4 a n d glucosamine C 6 H 1 3 0 5 N c a r b o -h y d r a t e s , but not lactic acid C 3 H 6 0 3 . The simple sugars are either polyhydroxy aldehydes or polyhydroxy ketones. The carbohydrates ordinarily also encompass all substances that are closely related to sugars, e.g. simple derivatives (amino sugars, carboxylic acids, etc.) and polymers of them (oligo- and polysaccharides), which will be discussed in Chapter XVII. 1. Nomenclature and Definitions 1 Aldoses and Ketoses. Carbohydrates differ from ordinary polyalcohols in that one of the alcohol groups is oxidized to a carbonyl group. We use glycerol as an example : 1 F o r international rules of nomenclature see Eur. J. Biochem. 21, 455-477 (1971). 2 9 0
eBook - PDF- P Karlson(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
C H A P T E R Simple Sugars, Monosaccharides The simple sugars constitute a subclass of the great class of natural substances, the carbohydrates. In sheer amount, the carbohydrates make up the bulk of organic substance on this earth. Though predominantly of plant origin, they constitute the principal component of the food of many animals and of man. Of the customary divisions of foodstuffs—protein, fats, and carbohydrates—the carbohydrates rank highest as energy suppliers. Many simple sugars contain carbon and the elements of water in the ratio of 1:1; this fact has caused the name carbohydrate to be given to this class of compounds. The designation originated at a time when real significance was attached to the empirical formula C x (H 2 0) n , which represents these substances as hydrates of the element carbon. Today we are no longer bound by the empirical formula; we call deoxyribose C 5 H 1 0 O 4 and glucosamine C 6 H 1 3 0 5 N carbo-hydrates, but not lactic acid C 3 H 6 0 3 . The simple sugars are either polyhydroxy aldehydes or polyhydroxy ketones. The carbohydrates ordinarily also encompass all substances that are closely related to sugars, e.g. simple derivatives (amino sugars, carboxylic acids, etc.) and polymers of them (oligo- and polysaccharides), which will be discussed in Chapter XVII. 1. Nomenclature and Definitions 1 Aldoses and Ketoses. Carbohydrates differ from ordinary polyalcohols in that one of the alcohol groups is oxidized to a carbonyl group. We use glycerol as an example: 1 For international rules of nomenclature see Eur. J. Biochem. 21, 455-477 (1971). 2 9 0 XV 1. NOMENCLATURE AND DEFINITIONS 291 Η Ο V I H O -C -H I CH 2 OH Η Ο V I H -C -O H I CH 2 OH H 2 C -O H ± 2 2 -H A -O H I Η C -O H -2 [H] CH 2 OH I 2 c=o I CH 2 OH L- D-Glyceraldehyde Glycerol Dihydroxyacetone Obviously, two dehydrogenation products are possible, either the aldehyde or the ketone.
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- 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.
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