Additional context

This document introduces the fundamental chemistry of carbohydrates, a critical area of study in biochemistry. Carbohydrates, often called saccharides, are organic compounds essential to life, playing diverse roles in energy storage, structural support, and cell signaling. Their basic formula, $ [C(H_{2}O)] $n, reflects their composition of carbon, hydrogen, and oxygen, initially leading to the idea that they were simply 'hydrates of carbon'. Glucose, a monosaccharide highlighted in the document with its chemical structure, serves as a prime example and is the body's primary energy source. Understanding carbohydrate chemistry builds upon core concepts in organic chemistry, such as functional groups (like aldehydes and ketones) and stereochemistry, which determines the three-dimensional arrangement of atoms in molecules like glucose and greatly influences their biological activity. This knowledge is foundational for comprehending more complex biological processes.

Course Title: B.I.C. 201

Chemistry of Biological Molecules

Dr (Mrs) P. C. Okorie

Topic: Chemistry of Carbohydrates

Topic Outline

• Introduction

• Definition

• functions of C.H.O.'s

• Classification of C.H.O.'s

• Stereochemistry of Monosaccharides

• Details of each class of C.H.O.'s

• Complex C.H.O.

Introduction

• The word carbohydrates is derived from the general formula [C(H sub 2.O.)] n that makes them seem to be "hydrates of carbon."

• The terms carbohydrate and saccharide are closely related.

• The most abundant carbohydrates are polysaccharides.

• Most important carbohydrate in the body which is a monosaccharide is Glucose

Definition

3 Definitions

Definition 1: Polyhydroxy aldehyde: An organic compound containing multiple hydroxyl (-OH) groups and an aldehyde (-CHO) group.

Definition 2: Polyhydroxy ketone: An organic compound containing multiple hydroxyl (-OH) groups and a ketone (C=O) group.

Definition 3: Hydrolysis: A chemical reaction in which a molecule is cleaved into two or more parts by the addition of water.

Carbohydrates may be defined as polyhydroxy aldehyde or polyhydroxy ketone or compound that yield these derivatives on hydrolysis.

Image summary: The image is a chemical structure diagram. It depicts the structure of D-Glucose. The structure includes a carbonyl group at the top, followed by a chain of carbon atoms, each bonded to hydrogen and hydroxyl groups, with a terminal hydroxymethyl group. The diagram indicates the arrangement of atoms within the glucose molecule.

Image summary: The image is a structural formula diagram. The diagram depicts the chemical structure of D-Fructose. The structure shows a carbonyl group (C=O) at the second carbon atom, which is a characteristic feature of ketoses like fructose.

• Complex C.H.O.'s may also contain such other elements as N, S and P, in addition to C, H & O.

• They are the most abundant class of organic compounds found in living organisms.

• They originate as products of photosynthesis – an endothermic reductive condensation of C-O-two, H.2.O, requiring light energy and the pigment chlorophyll.

• Ketose contains a ketone (C-O) group, while aldose contains an aldehyde (C.H.O.) group

Functions of Carbohydrates

• Carbohydrates are the key source of energy used by living things (e.g. glucose-Supplies about 4 kilocalories per gram).

• They therefore serve as storehouses of chemical energy (starch in plants & glycogen in humans)

• Components of Supportive/ Structural material in; -Plants (cellulose),

-Crustacean shells and in exoskeleton of insects (chitin) and

-Cell membrane and connective tissues (acidic mucopolysaccharides) in animals

- Source of fibre in diet.

• Essential components of nucleotides in nucleic acids (D-ribose and 2-deoxy-D-ribose).

- – -Ribose (a 5-carbon monosaccharide) is an important component of coenzymes (F.A.D. & N.A.D.) and the genetic material R.N.A.

- – -The 2-deoxyribose is a component of D.N.A.

• key intermediates in metabolism -see later in metabolism.

• Play important roles in detoxification (e.g. glucoronic acids)

• others

• Play key roles in immune system, blood clotting, fertilization and development.

• Involved in biological recognition processes on cell

• surfaces (cell communication).

General Chemical Features of Carbohydrates

• They have at least 1 and often 2 or more asymmetric carbon centres

• They exist either in linear or ring forms

• They form polymeric structures via glycosidic bonds

• They have the potential to form multiple hydrogen bonds with water and other molecules in their environment.

These features are responsible for the many functions of C.H.O.'s.

Classification of Carbohydrates

There are different basis for classification of carbohydrates.

• Based on number of sugars: 1) Monosaccharides, 2) Disaccharides, 3) Oligosaccharide 4) Polysaccharides.

• Based on functional groups: 1) Aldoses 2) Ketoses.

• Based on the complexity of the carbohydrate.

• Based on functions: 1) Storage C.H.O.'s eg starch and glycogen 2) Structural C.H.O.'s eg cellulose and chitin (see later).

Based on the number of sugar molecule they contain:

Table summary: The table illustrates the structural differences between different types of saccharides. Monosaccharides and disaccharides have simpler structures, while oligosaccharides are composed of short chains of units, and polysaccharides consist of much longer chains.

Carbohydrates are classified by their functional groups as shown below;

• Sugars that contain an aldehyde (-C.H.O.) group are called Aldoses.

• Sugars that contain a keto group (-C=O) are called Ketoses.

They can also be classified as

• Simple carbohydrates – Monosaccharide – Disaccharide

• Oligosaccharides

• Complex carbohydrates — Polysaccharides

Classification of C.H.O.'s (Examples)

Figure 13.1 summary: This figure is a hierarchical diagram that illustrates the classification of carbohydrates. The diagram categorizes carbohydrates into three primary groups: monosaccharides, oligosaccharides, and polysaccharides. Oligosaccharides are further divided into disaccharides and trisaccharides, while polysaccharides are divided into structural and storage polysaccharides. Monosaccharides are further divided into trioses, tetroses, pentoses, hexoses, and heptoses. The diagram indicates that carbohydrates are diverse, varying in the number of sugar units they contain and their specific functions, such as structural support or energy storage.

The Monosaccharides (simple sugars)

• They cannot be hydrolysed into simpler forms under mild conditions.

• Generally contain 3 to 7 carbon atoms

• May be classified as: 1) Aldoses with aldehyde functional grps (-C.H.O.) or Ketoses with keto grps (-C=O).

• Simplest aldose is glyceraldehyde and the simplest ketose is dihydroxyacetone; each with 3 carbon atoms is they are trioses.

The Monosaccharides contd

• May therefore be classified based on number of carbon atoms

1) The trioses - contain 3 carbon atoms eg's glyceraldehyde, dihydroxyacetone - see earlier

2) The tetroses - contain 4 carbon atoms eg's erythrose, erythrulose, threose.

3) The Pentoses-contain 5 carbon atoms eg's arabinose, Ribose, Ribulose, Xylose, Xylulose, Lyxose.

4) The Hexoses - contain 6 carbon atoms eg's glucose, fructose, galactose, mannose, sorbose.

5) The Heptoses - contain 7 carbon atoms eg's Sedoheptulose, Mannoheptulose.

2 Definitions

Definition 1: Aldose: A monosaccharide (simple sugar) that contains an aldehyde group.

Definition 2: Ketose: A monosaccharide (simple sugar) that contains a ketone group.

(see the structures below, classify the above as aldoses and ketoses in a tabular form-assignment

The Monosaccharides (simple sugars – no of carbon)

Classification of Monosaccharides

Table 1 summary: The tables present different types of sugars based on the number of carbons, including trioses, tetroses, pentoses, hexoses, and heptoses, and their classification as aldoses or ketoses. It also shows the structure of different hexoses (glucose, galactose, and fructose). Finally, it presents various GAGs with their composition, tissue distribution, and functions.

Structures - The Trioses

H-C=O H-C-O.H. C.H. sub 2.O.H.

Definition

Aldotriose: A monosaccharide with three carbon atoms and an aldehyde group.

D-glyceraldehyde (Aldose) an aldotriose

Structures - The Trioses

Math summary: This represents the chemical structure of a molecule. It shows a carbon atom double bonded to an oxygen atom, with each carbon atom also bonded to a hydroxymethyl group.

Tetroses

Image summary: The image is a structural formula diagram. It depicts the chemical structure of D-Erythrose, a monosaccharide with four carbon atoms. The structure shows a carbonyl group at the top, followed by three carbon atoms, each bonded to a hydroxyl group, and a hydroxymethyl group at the bottom. It can be inferred that D-Erythrose is a tetrose sugar, specifically an aldose, due to the presence of an aldehyde group.

Image summary:The image is a structural formula diagram. The diagram depicts the chemical structure of glyceraldehyde. The molecule contains an aldehyde group, two hydroxyl groups, and a carbon chain. It is a simple sugar molecule.

Heptoses

Image summary: The image shows chemical structural formulas. The image presents two molecules with similar structures. The molecules differ in the arrangement of hydroxyl groups on the carbon chain.

Family tree of D-aldoses up to hexoses:

Image summary: This image is a diagram illustrating the relationships between different aldoses. The diagram starts with an aldotriose and branches out to aldotetroses, aldopentoses, and finally aldohexoses. The diagram shows how the different aldoses are structurally related, with each level of branching representing a different number of carbon atoms in the sugar molecule. The structure of each sugar is shown, with the key difference between the sugars being the stereochemistry at one or more carbon centers. The diagram illustrates how a small change in the structure of a sugar can lead to a different molecule with different properties.

Family tree of D-ketoses up to hexoses

Image summary: The image is a flowchart that depicts the chemical structures of various monosaccharides and their relationships. It starts with dihydroxyacetone, which transforms into D-erythrulose. D-erythrulose then branches into D-ribulose and D-xylulose. Finally, D-ribulose and D-xylulose transform into D-psicose, D-fructose, D-sorbose and D-tagatose respectively. The flowchart illustrates how one monosaccharide can be converted into another through a series of chemical reactions.

The Disaccharides

• On hydrolysis yield 2 simple sugars: eg's

1) Maltose (Glu + Glu)

2) Isomaltose (Glu + Glu)

2) Lactose (Glu + Gal)

5) Sucrose (Glu + Fru)

5) Cellobiose (Glu + Glu)

v sub i Gentiobiose (Glu plus Glu)

2) Trehalose (Glu + Glu)

2) Melibiose (Glu + Gal)

(structures to follow)

Monosaccharides Link to Form Disaccharides

Image summary: The image is a diagram illustrating the formation of disaccharides from monosaccharides. The diagram depicts three examples: the formation of maltose from two glucose molecules, the formation of sucrose from glucose and fructose, and the formation of lactose from galactose and glucose. In each case, a water molecule is released during the formation of the disaccharide. Monosaccharides combine through dehydration reactions to form disaccharides. Different combinations of monosaccharides result in different disaccharides.

Naming of the glycosidic bonds in disaccharides

Definition

Glycosidic bond: A type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.

• Glycosidic bonds between sugars are named according to the numbers of the connected carbons and with regard to the position of the anomeric hydroxyl group of the first sugar involved in the bond.

Definition

Configuration: The spatial arrangement of atoms in a molecule that is fixed and cannot be changed without breaking chemical bonds.

• If this anomeric hydroxyl is in the a configuration, then the linkage is an a-bond.

• If it is in the beta configuration, then the linkage is a beta-bond. Lactose, for example, is synthesized by forming a glycosidic bond between carbon 1 of beta-galactose and carbon 4 of glucose.

Therefore, the linkage is a beta 1 to 4 glycosidic bond (see below).

Definition

Reducing sugar: Any sugar that is capable of acting as a reducing agent because it has a free aldehyde or ketone group.

• [Note: Because the anomeric end of the glucose residue is not involved in the glycosidic linkage, it (and, therefore, lactose) remains a reducing sugar-see later.]

Chemistry of Carbohydrates

Definition

Disaccharide: A carbohydrate composed of two monosaccharides joined by a glycosidic bond.

• Maltose, or malt sugar, is a disaccharide formed in the breakdown of starch.

- Malted barley contains high levels of maltose. The glucose in the maltose of malted barley can be converted to alcohol by yeast.

• The glycosidic bond in maltose is a 1 to 4.

• Maltose is a reducing disaccharide due to a free functional group on the second sugar unit.

• The a(1→4) glycosidic bond of maltose is broken by an enzyme called maltase in the body to give two glucose units.

Image summary:The image displays a close-up shot. The image showcases a handful of grain held in a hand, with a larger pile of the same grain in the background. The grain appears to be barley or a similar cereal crop. The image conveys a sense of abundance and harvest.

Image summary: The image is a structural formula diagram. It shows the chemical structure of alpha-D-Maltose. The structure is composed of two glucose units, one alpha-D-glucose and one D-glucose, connected by an alpha(1 to 4) glycosidic bond. One glucose unit has a free anomeric carbon. Maltose is a disaccharide formed by a bond between two glucose molecules.

Disaccharides

Image summary: The image is a structural formula diagram. It depicts a maltose molecule, which is a disaccharide formed by an alpha-1-4 glycosidic bond between two glucose molecules. The diagram shows the arrangement of atoms and bonds within the maltose molecule. The structure illustrates how two glucose units are linked together to form a more complex sugar.

Lactose

Image summary: The image is a chemical structure diagram. The diagram illustrates the formation of lactose from galactose and glucose. The process involves a dehydration reaction where a water molecule is removed, resulting in the formation of a bond between the two monosaccharides to form the disaccharide, lactose.

Definition

Lactase: An enzyme that catalyzes the hydrolysis of lactose into glucose and galactose.

- Lactose, or milk sugar, is found in mammalian milk and milk products and is hydrolysed into galactose and glucose by lactase in humans and by beta -galactosidase in bacteria.

• Intolerance to lactose occurs in people without lactase.

• When lactose remains undigested, intestinal bacteria breaks it down, producing abdominal gas and cramping.

• The glycosidic bond in lactose is beta (1→4): it occurs between C.1. of a beta-galactose and C.4. of a glucose.

Definition

Anomeric carbon: The carbon atom in a cyclic sugar that is derived from the carbonyl carbon (the aldehyde or ketone group) of the open-chain form.

- Because the anomeric carbon on the glucose unit is free (not in a glycosidic bond), lactose is a reducing disaccharide sugar.

Image summary: The image is a combination of a photograph and a structural diagram. The photograph displays dairy products such as milk and cheese. The structural diagram depicts beta-D-Lactose, which is composed of beta-D-Galactose and D-Glucose units connected by a beta(1 to 4) glycosidic bond. The diagram also highlights the free anomeric carbon.

Lactose

Image summary: The image is a structural formula diagram. It depicts a disaccharide formed by a beta-1-4 glycosidic bond between galactose and glucose. The structural formula shows the arrangement of atoms and bonds in the disaccharide molecule. The linkage between the two monosaccharides is a beta-1-4 glycosidic bond, indicating the stereochemistry and the specific carbon atoms involved in the bond formation. The diagram provides insight into the molecular structure and composition of the disaccharide.

Sucrose

Image summary:The image is a chemical structure diagram. It illustrates the process of combining glucose and fructose to form sucrose. During this process, a water molecule is released.

Definition

Sucrose: A disaccharide composed of glucose and fructose linked by an α-1,β-2-glycosidic bond. Commonly known as table sugar.

- Sucrose is the most abundant disaccharide in nature: Sucrose is found in sugar cane(commonly used table sugar) and sugar beets. They contribute to the daily caloric intake.

• It is hydrolysed by sucrase (invertase) in the git to produce glucose and fructose

When glucose and fructose join in an a, b, 1 to 2 glycosidic bond, sucrose is formed.

Both anomeric carbons are bonded (C.1. of glucose and C.2. of fructose). Because there is no free anomeric carbon, sucrose is not a reducing sugar.

Image summary: The image is a chemical structure diagram. It depicts the formation of sucrose from an alpha-D-glucose unit and a beta-D-fructose unit. The diagram highlights the glycosidic bond that links the two monosaccharides together, specifically showing the bond between carbon one of glucose and carbon two of fructose. The image suggests that sucrose, commonly known as cane sugar, is a disaccharide formed by the combination of glucose and fructose through a glycosidic bond.

Cellobiose

Image summary: This is a chemical structural diagram. The diagram depicts a Beta-1-4 glycosidic bond between two glucose molecules. This bond connects the first carbon atom of one glucose molecule to the fourth carbon atom of the other glucose molecule, forming a disaccharide. The linkage is in the beta configuration. The resultant disaccharide is cellobiose.

Image summary: The image is a structural formula diagram. It depicts a beta-1-4 glycosidic bond between two glucose molecules. The diagram illustrates the connection between carbon number one of one glucose molecule and carbon number four of another glucose molecule, forming a disaccharide.

Isomaltose

It is also contains two moles of glucose.

They linked by a, one through six, glycosidic linkage.

Definition

Glycogen: The storage form of glucose in animals, a highly branched polysaccharide.

It is derived from the digestion of starch & glycogen.

Definition

Isomaltase: An enzyme that hydrolyzes isomaltose, a disaccharide similar to maltose but with a different glycosidic bond.

It hydrolyzed to glucose in the intestinal tract by an enzyme called isomaltase.

Trehalose

It is also one of the disaccharide having two units of glucose linked by a-(1 to 1) glycosidic linkage.

It is a non reducing disaccharide.

Definition

Trehalose: A non-reducing disaccharide consisting of two glucose molecules linked by an α,α-1,1-glycosidic bond.

Yeast and fungi are the sources of trehalose.

Image summary: The image is a structural formula diagram. It depicts the molecular structure of gentiobiose. Gentiobiose is a disaccharide formed by a beta-1-6 glycosidic bond between two glucose molecules. The structure shows the arrangement of atoms and bonds within the molecule, including the position of hydroxyl groups.

Image summary:The image is a structural formula diagram. The diagram depicts a disaccharide formed by two glucose molecules connected via an alpha-1-1-glycosidic bond. Both glucoses are in their typical six-membered ring form, with hydroxyl and hydrogen groups attached to the carbon atoms. The glycosidic bond is formed between the carbon number one of both glucose molecules, with the oxygen atom bridging the two rings. The structure illustrates the formation of a glycosidic bond between two monosaccharides, resulting in a disaccharide. The alpha configuration at the anomeric carbon is specified by the orientation of the bond relative to the sugar ring.

treehalose

The Oligosaccharides

• Contain 3 - 10 simple sugars

• They mainly form components of complex C.H.O.'s - eg glycoproteins.

• Some antibiotics are oligosaccharides or contain oligosaccharide groups eg streptomycin, aburamycin C, sulfurmycin B, Bleomycin A.2.

Oligosaccharides

• Humans lack the enzymes necessary to digest them

• Intestinal microflora digest and ferment them, producing gas – Cause bloating, discomfort, and flatulence

• Food sources

- – Legumes, beans, cabbage, brussels sprouts, broccoli

The Trisaccharides

• On hydrolysis yield 3 simple sugars: eg's

1) Maltotriose (Glu + Glu + Glu)

2) Raffinose (Gal + Glu + Fru) - not digested/absorbed in human git due to lack of appropriate enzymes.

(assignment-check the structures later and note the bonds joining them)

The Tetrasaccharides

• On hydrolysis yield 4 simple sugars: eg Stachyose (Gal + Gal +Glu + Fru) - not digested/absorbed in human git due to lack of appropriate enzymes.

(look up the structures later and note the bonds linking them up)

check the linker tetrasaccharides in the glycosaminoglycans-G.A.G.'s

The Structure of an Oligosaccharide

Image summary: The figure is a structural chemical formula. It depicts the chemical structure of raffinose. Raffinose is shown to be composed of galactose and sucrose molecules. Sucrose is composed of two other molecules.

Structures of raffinose and stachyose

Image summary:The image shows chemical structure diagrams. The diagrams illustrate the molecular structures of Raffinose and Stachyose. Stachyose has one more monosaccharide unit compared to Raffinose, making it a larger molecule.

The Polysaccharides

• They contain many (more than 10) monosaccharides linked by glycosidic bonds.

• They are classified into:

1) Homopolysaccharides: these are formed by the same kind of monosaccharides eg's starch, glycogen and cellulose. Each of them are formed by hundreds of molecules of glucose linked by glycosidic bonds.

Definition

Heteropolysaccharides: Polysaccharides composed of two or more different monosaccharide units.

2) Heteropolysaccharides:

These polysaccharide molecules are formed by different kinds of monosaccharides.

2 Definitions

Definition 1: Hyaluronic acid: A glycosaminoglycan found in connective tissue, synovial fluid, and other tissues; it provides lubrication and cushioning.

Definition 2: Glucuronic acid: A sugar acid derived from glucose, often found in glycosaminoglycans.

Hyaluronic acid, formed by thousands of alternating units of N-acetyl glucosamine and glucuronic acid, is an example of heteropolysaccharide.

Definition

Proteoglycans: Macromolecules consisting of a core protein covalently attached to one or more glycosaminoglycan chains.

Other eg's include: chondroitin sulfate, heparin, keratan sulfate, dermatan sulfate. These are called glycosaminoglycans which link with proteins to form even larger molecules called Proteoglycans-see later

• Polysaccharides may also be classified based on the structure (linkages of the monosaccharides).

1) Branched polysaccharides eg's: starch and glycogen.

2) Unbranched/Linear polysaccharides eg's: amylose and cellulose.

Polysaccharides

• They can also be classified into

• Digestible polysaccharides: - Starch - Amylose - Amylopectin - Glycogen

• Non-digestible polysaccharides: fibers – Soluble fiber – Insoluble fiber

Polysaccharides

• Digestible polysaccharide s:

- – Starch

• Amylose • Amylopectin

- Glycogen

Image summary: The image shows a diagram of starch composition in potatoes. The diagram presents the molecular structures of amylose and amylopectin, the two primary components of starch. Amylose is depicted as an unbranched chain of glucose monomers linked by glycosidic bonds, while amylopectin is shown as a branched chain with both glycosidic bonds forming the main chain and other glycosidic bonds at the branch points. Amylopectin constitutes a significantly larger proportion of starch compared to amylose.

Starch

Definition

Homopolymer: A polymer made from only one type of monomer.

Is reserve carbohydrate form in plants. right arrow e.g - potato A homopolymer composed of D-glucose units held by a-glycosidic bonds.

2 Definitions

Definition 1: Amylose: A linear polysaccharide composed of glucose units linked by α(1→4) glycosidic bonds, a component of starch.

Definition 2: Amylopectin: A branched polysaccharide composed of glucose units linked by α(1→4) and α(1→6) glycosidic bonds, a component of starch.

It composed of two constituents, water soluble amylose (15 to 20%) and water insoluble amylopectin (80 to 85%).

Starch

Chemically, amylose is a long unbranched chain of 200 to 1000 of D-glucose units linked by (1 to 4) bonds.

Amylopectin, is a branched chain with (1 to 6) bonds at the branching points and (1 to 4) bonds everywhere else.

Amylopectin contains few thousands of units looks like a branched tree. (20 to 30 units/ branch)

2 Definitions

Definition 1: Amylase: An enzyme that catalyzes the hydrolysis of starch into smaller carbohydrates like dextrins and maltose.

Definition 2: Dextrin: A group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen.

Starch is hydrolyzed by the enzyme amylase to liberate dextrin and finally maltose and glucose units.

Polysaccharides

• Starch

— Plants store glucose in chains of starch

• Amylose

—Straight chain

—More resistant to digestion

—Resistant starch

✓ May improve health of digestive tract

✓ May improve glucose tolerance

✓ May stimulate growth of beneficial intestinal bacteria

• Amylopectin

- —Branched chains

- —Easier to digest

Amylose

• A linear homopolysaccharide (see structure)

• Made up of D-glucose units linked by alpha 1,4-glycosidic bonds

• Insoluble in water

• Gives blue colour with iodine

• Forms the outer layer of the starch granule

• Composes about 30% of the granule

Hydrolysis by alpha amylase

Image summary:The image is a diagram that shows a polysaccharide. It depicts a chain of glucose molecules linked together. The diagram illustrates that polysaccharides are formed through the repeated connection of monosaccharide units, in this case, glucose.

Amylopectin

• A branched homopolysaccharide (see structure)

- Made up of D-glucose units linked by alpha minus 1,4-glycosidic bonds at the linear chains and alpha minus 1,6-glycosidic bonds at the

- branches

• Insoluble in water.

• Gives red-violet colour with iodine

• Forms the inner layer of the starch granule • Composes about 70% of the granule

Image summary: The image is a representation of the amylopectin structure. The amylopectin is composed of several glucose molecules linked together. The structure shows a branched arrangement of glucose molecules, indicating that amylopectin is a branched polysaccharide.

• Linear chains hydrolysed as in amylose but alpha minus 1,6 bonds are hydrolyzed by alpha minus 1,6 glucosidase

• Amylopectin shows a branch at each 24 to 30 units of glucose.

Structure of amylose and amylopectin

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Glucose

Image summary:The image is a diagram illustrating the molecular structures of amylose and amylopectin. The diagram shows amylose as a linear chain of glucose molecules. Amylopectin is depicted as a branched structure, also composed of glucose molecules. Amylopectin has a more complex and branched structure compared to the linear structure of amylose.

Dextrins

- ▶ Partial hydrolysed products of starch by acids or enzymes.

- Starch is sequentially hydrolyzed through different dextrins and finally to maltose and glucose.

- The various intermediates are soluble starch, amylodextrins, erythrodextrins, and achrodextrins.

- All dextrins have free sugar groups and can show mild reducing property.

Glycogen

• A storage glucose in animal tissues (mainly found to the power of 8 the liver (400 kilocalories) and muscles (1400 kilocalories)) • A branched homopolysaccharide composed of D-glucose units linked by alpha minus 1,4-glycosidic bonds at the linear chains and alpha minus 1,6-glycosidic bonds at branches.

Image summary: The image is a schematic diagram showing a dendritic structure. It illustrates a central point from which multiple branches extend outwards in a radial pattern. The branches further divide into smaller segments, resembling a tree-like structure. This structure suggests a hierarchical or branching network, where elements are interconnected and radiate from a central node.

• Structure is similar to amylopectin but with more complex branching

• Hydrolyzed by alpha amylase and alpha 1, comma 6, hyphen glucosidase to yield maltose and glucose.

• Glycogen shows a branch at each 8 to 10 units of glucose

Structure of Glycogen

Image summary:The image is a chemical structure diagram. It depicts two types of glycosidic bonds, specifically alpha-1,4 and alpha-1,6 linkages. The diagram illustrates how monosaccharide units are connected through these bonds to form a larger polysaccharide structure. The presence of both alpha-1,4 and alpha-1,6 glycosidic bonds suggests the formation of a branched polysaccharide.

• Glycogen

- — Storage form of glucose in animals

- — Long, branched chains of glucose

- — Stored in liver and muscle

- – Liver glycogen response to blood glucose (B.G.) levels

- B.G. ☐ glycogen breakdown ☐ B.G.

- — Muscle glycogen can be broken down for energy for the muscle

The Comparison of Starch and Glycogen Molecules

Starch: Two types of polysaccharides in starch are amylose (straight chain) and amylopectin (branched). b Glycogen: The storage form of glucose in animals, including humans. Glycogen is more branched than amylopectin. Each new glycogen needs a special protein to attach the glucose molecule.

Image summary:The image is a diagram that illustrates the molecular structures of starch components and glycogen. The diagram depicts amylopectin, amylose, and glycogen. Amylopectin and glycogen exhibit a branched structure, while amylose is portrayed as a more linear chain. The branching pattern appears more extensive in glycogen compared to amylopectin, suggesting structural differences between these two polysaccharides.

Structural Polysaccharides

Cellulose

• Cellulose contains glucose units bonded beta (1 to 4).

- This glycosidic bond configuration changes the three-dimensional shape of cellulose compared with that of amylose.

• The chain of glucose units is straight. This allows chains to align next to each other to form a strong rigid structure-see later.

Polysaccharides, Continued

Cellulose

• Cellulose is an insoluble fiber in our diet because we lack the enzyme cellulase to hydrolyze the beta, one to four, glycosidic bond.

• Whole grains are a good source of cellulose.

• Cellulose is important in our diet because it assists with digestive movement in the small and large intestine.

• Some animals and insects can digest cellulose because they contain bacteria that produce cellulase.

Cellulose

- Chief constituent of plant cell wall.

- ➔ An unbranched polymer of glucose linked by beta minus open parenthesis 1 minus 4 close parenthesis glycosidic linkages.

- Since humans lack an enzyme cellulase that can hydrolyse beta-(1 to 4) glycosidic linkages, cellulose cannot be digested and absorbed.

- ☑ has no food value unlike starch.

Importance of Cellulose

Definition

Cellulose: A structural polysaccharide consisting of glucose monomers linked by β(1→4) glycosidic bonds, the main component of plant cell walls.

Cellulose, though not digested, has great importance in human nutrition.

It is a major constituent of fibre, the non-digestable carbohydrate.

The functions of dietary fibre include

- decreasing the absorption of glucose and cholesterol from the intestine,

- ➔ increasing the bulk of stool.

- Aids intestinal mobility acts as stool softener

- Prevent constipation.

➔ It reduces incidence of ....

Negative C.V.D.

- ☑ Colon cancer

- diabetes

Polysaccharides

•Fiber

- – Non-digestible polysaccharide – Provides no energy

– Classification

Image summary: The image is a photograph. It shows a plant stem that transitions into a mass of fibers. The stem appears to be a more solid structure, while the fibers are much more delicate and spread out. The plant matter has a natural, somewhat raw appearance, suggesting it could be in the process of being broken down or processed into a different form. The transition from stem to fiber indicates a change in the plant's structure, possibly for seed dispersal or some other biological function.

• Soluble

—Pectins, beta-glucan, some gums, mucilage

–Easily fermented by intestinal bacteria producing

• Carbon dioxide, methane, some fatty acids

• Insoluble

- –Cellulose, lignin, some hemicelluloses –Not easily fermented

Fiber Health Benefit-a recap

• Soluble fibers

– Slow gastric emptying and may delay absorption of some nutrients

• Helps reduce serum cholesterol

• Improve appetite control

• Normalize blood glucose levels

– May help protect against colon cancer

• Insoluble fibers

— Relieves constipation

• Most plant foods contain both soluble and insoluble fibers

Inulin

• Inulins are polymers composed mainly of fructose units, and typically have a terminal glucose.

They are linked by beta of 2, 1 glycosidic bonds.

• Because of the beta(2,1) linkages, inulin is not digested by enzymes in the human git

• Standard inulin is slightly sweet

• It is soluble in water.

• Used to determine glomerular filtration rate (kidney fxn)

Chitin

Structural Polysaccharides:

• Chitin is made up of a modified beta-D-glucose called N-acetylglucosamine with beta of 1 to 4 glycosidic bonds.

- Like cellulose, chitin is a strong material with many uses, one of which is a surgical thread that biodegrades as a wound heals.

- Chitin is present in many insects' exoskeletons and serves to protect them from water. Because of this property, chitin can be used in waterproof paper.

• When ground, chitin becomes a powder that holds in moisture, and it can be added to cosmetics and lotions.

Polysaccharides, Chitin

Hetero polysaccharides

• These are polysaccharides containing more than one type of sugar residues

• Glycosaminoglycans, (G.A.G.'s or mucopolysaccharides) They are long, usually unbranched, composed of a repeating disaccharide units

• They are negatively charged heteropolysaccharide chains (polyanions)

• The amino sugar is either D-glucosamine or D-galactosamine in which the amino group is usually acetylated, thus eliminating its positive charges

• The amino sugar may also be sulfated on carbon 4, 6, or on a monoacetylated nitrogen.

• The acidic sugar is either D-glucuronic acid or its carbon 6 epimer, L-uronic acid. For example Hylauronic acid, Heparin and chondroitin sulphate.

Functions of Glycosaminoglycans (G.A.G.S.)

• They have the special ability to bind large amounts of water, there by producing the gel-like matrix that forms the basis of the body's ground substance.

• Since they are negatively charged, for example, in bone, glycosaminoglycans attract and tightly bind cattions like ca plus plus, they also take-up Na to the power of plus and K to the power of plus

• G.A.G.'s stabilize and support cellular and fibrous components of tissue while helping maintain the water and salt balance of the body.

• Its essential components of the extra cellular matrix, G.A.G.'s' play an important role in mediating cell-cell interactions

• Ground substance is a part of connective tissue, which is a gel like substance containing water, salt, proteins and polysaccharides.

• An example of specialized ground substance is the synovial fluid, which serves as a lubricant in joints, and tendon sheaths.

Mucopolysaccharides

- ▶ Heteroglycans made up of repeating units of sugar derivatives, namely amino sugars and uronic acid.

- Commonly known as glycosaminoglycans. (G.A.G.'s)

- Acetylated amino groups, besides sulfate and carboxyl groups are generally present in their structure.

- Presence of sulfate and carboxyl groups contributes to acidity of the molecules, making them acid mucopolysaccharides.

- Some of them found in the combination with proteins to form mucoproteins or mucoids or proteoglycans.

- ➔ Mucoproteins may contain...

- up to 95% carbohydrate and

- 5% protein.

Mucopolysaccharides

Definition

Mucopolysaccharides: An older term for glycosaminoglycans, referring to their viscous, mucus-like properties.

➔ Mucopolysaccharides are essential components of tissue structure.

2 Definitions

Definition 1: Collagen: The main structural protein in the extracellular matrix found in various connective tissues.

Definition 2: Elastin: A protein in connective tissue that allows tissues to stretch and recoil.

The extra cellular spaces of tissue (connective tissue, cartilage, skin, blood vessels, tendons) consist of collagen and elastin fibers embedded in a matrix or ground substance.

The ground substance is predominantly composed of G.A.G.'s.

The important mucopolysaccharides are...

▶ Hyaluronic acid

Chondroitin 4-sulfate

➔ Heparin

Dermatan sulfate and

Keratan sulfate

• G.A.G.'s are the Major Gel Forming Components of The Extracellular Matrix of Connective Tissue that is the anionic groups (Carboxy & Sulfate groups) being Strongly Hydrophilic tend to bind large amounts of water to produce the gel-like Matrix.

• The Heteropolysaccharide chains of G.A.G.'s repel one another & thus exist in extended conformation in solutions. This produces the slippery consistency of Mucus secretions & Synovial Fluid in joints.

Hyaluronic Acid

• Disaccharide unit: N-acetylglucosamine and glucoronic acid

• Different from other gag:

Not sulfated, not covalently attached to protein, and not limited to animal tissue but also found in bacteria.

• Serves as a lubricant and shock absorber

• Found in synovial fluid of joints, vitreous humor of the eye, the umbilical cord, loose connective tissue, and cartilage.

Image summary:The image is a chemical structural diagram. It depicts a disaccharide composed of two hexose rings connected by a glycosidic bond. The hexose on the left has a carboxylate group attached to one of its carbons, while both hexoses have hydroxyl groups attached to other carbons. The glycosidic bond connects carbon 1 of the right hexose to carbon 4 of the left hexose. The structure represents a repeating unit in a polysaccharide, suggesting it may be part of a larger carbohydrate molecule. The presence of the carboxylate group indicates that the polysaccharide is acidic.

Heparin

• Disaccharide unit:

• Glucosamine and glucoronic or iduronic acid; most glucosamine residues are bound in sulfamide linkages; sulfate also found on C.3. or C.6. of glucosamine and C.2. of uronic acid.

• Alfa linkage joins the sugars

• Unlike other G.A.G.'s that are extracellular compounds, heparin is an intracellular component of mast cells that line arteries, especially in liver, lungs and skin.

• Serves as an anticoagulant

• Strongly Acidic due to presence of more Sulfate groups

Heparan Sulfate

• This is an extracellular gag found in basement membranes & is an essential component of cell surfaces.

• It is Structurally Similar to Heparin but has a Lower Molecular Weight, contains More Acetyl Groups & Less Sulfate Groups.

• It Determines Charge Selectiveness of the Renal Glomerulus.

Chondroitin 4-and 6 Sulfates

• Disaccharide unit:

• N-acetylgalactosamine with S on either carbon (C) 4 or C.6. and glucoronic acid

• Most abundant gag in the body

• Found in cartilage, tendons, ligament and ay-or-tuh

• Form proteoglycan aggregates, through noncovalent association with hyaluronic acid

• In cartilage, bind collagen and hold fibres in a tight, strong network.

Image summary:The image is a chemical structure diagram. It illustrates the repeating disaccharide unit of Chondroitin 4-sulfate. The structure consists of D-Glucuronic acid and N-Acetylgalactosamine 4-sulfate linked together. The presence of a sulfate group on the N-Acetylgalactosamine indicates that it is a sulfated glycosaminoglycan.

Dermatan Sulfate

• Disaccharide unit:

N-acetylgalactosamine and L-iduronic acid (with variable amounts of glucoronic acid) with S on C.4.

• Found in skin, blood vessels, and heart valves

Image summary:The image is a structural formula diagram. It depicts the chemical structure of glucuronic acid. The structure shows a six-membered ring with an oxygen atom within the ring, characteristic of a sugar. Several hydroxyl groups (OH) are attached to the ring, along with hydrogen atoms (H). One carbon atom is bonded to a carboxylate group (COO-), which is a key feature distinguishing glucuronic acid from glucose.

Keratan Sulfates(K.S.)1 and 11

• disaccharide Unit:

• N-acetylglucosamine and galactose (no uronic acid) and; S may be present on C.6. of either sugar.

• Most heterogeneous gag because they contain additional monosaccharides such as L-fucose, N-acetyl-neuraminic acid, and mannose

• K.S. 1 found in corneas; K.S.11 found in loose connective tissue proteoglycan aggregates with chondrontin sulfate

Structure

Image summary:The image is a chemical structure diagram. It depicts a disaccharide composed of two modified monosaccharide units linked together. One unit contains a sulfate group, while the other has an N-acetyl group. The structure suggests a complex carbohydrate or glycosaminoglycan fragment. The presence of sulfate and N-acetyl modifications indicates that this molecule may have specific biological functions, such as cell signaling or extracellular matrix interactions.

Complex Carbohydrates

• Major complex carbohydrates are the Glycoproteins and the Glycolipids

• Many proteins and lipids have complex arrays of covalently attached oligosaccharides which serve a variety of functions. These include:

• Hydrophilicity of sugars alters the polarity and thus solubility of the molecule

• The oligosaccharide chains may affect the folding of peptides and influence protein structure

• The bulkiness of the sugars may protect the molecule from degradation

Complex Carbohydrates contd

• The sugars may provide recognition sequences for receptor-ligand interactions

• The sugars may act as target molecules for transport to a particular site in/out of the cell.

Glycoprotein

A "Typical" Membrane Glycoprotein

Image summary: The image is a labeled illustration of a typical membrane glycoprotein. The illustration depicts a lipid bilayer with a protein spanning the membrane, showing the extracellular, hydrophobic, and intracellular domains. The protein also has a carbohydrate moiety attached to the extracellular domain, composed of mannose and N-Acetylglucosamine. The polypeptide chain is also shown.

Monosaccharides

• Three important monosaccharides

- Glucose

- Fructose

- — Galactose

Glucose

• Also called a hexose sugar or dextrose • Principle building block of all other carbohydrates

– Part of every disaccharide

– Only monosaccharide in starch and glycogen.

• Typically exists in the ring form

• Most abundant monosaccharide in the body

• The preferred and main source of energy for the brain and red blood cells D-glucose

Image summary:The image is a structural formula diagram. It depicts a molecule containing carbon, hydrogen, and oxygen atoms. The molecule has a chain of carbon atoms with hydrogen atoms and hydroxyl groups attached to them. There are more hydroxyl groups attached to the carbon atoms than other groups. The presence of multiple hydroxyl groups and an aldehyde group at the end of the carbon chain suggests that the molecule is a carbohydrate, specifically a monosaccharide like glucose.

Fructose

• Also called levulose

• Sweetest of natural sugars

• Isomer of glucose

• Typically found as a subunit of sucrose

• Metabolized into glucose by the liver

• Found in fruit, honey, and high fructose corn syrup.

Image summary:The image is a still life photograph. It shows liquid being poured from a clear container into a small clear bowl. In the background are some green apples on a plate. The image depicts the process of extracting or preparing apple juice or cider, or possibly using apple cider vinegar.

Image summary: The image is a structural formula. It depicts a carbohydrate molecule. The molecule contains a carbonyl group and multiple hydroxyl groups, which is characteristic of sugars. The presence of a carbonyl group suggests that this could be a ketose sugar, specifically fructose.

Image summary:The image is a structural formula diagram. It depicts a cyclic molecule containing carbon, hydrogen, and oxygen atoms. The molecule is a five-membered ring with one oxygen atom within the ring structure. The molecule has multiple hydroxyl groups attached to the ring. Two hydroxymethyl groups are also attached to the ring. The structure represents a monosaccharide. Based on the structure, it is likely a fructose molecule.

Galactose

• Not usually found free in nature in large quantities

• A carbon 4 Epimer of glucose

• Typically found as a subunit of lactose

• Converted to glucose in the liver by an enzyme called epimerase.

Image summary:The image is a structural formula diagram. It illustrates the chemical structure of D-Galactose. The structure displays a six-carbon monosaccharide, with a carbonyl group and multiple hydroxyl groups attached to the carbon chain. The arrangement of atoms and functional groups indicates that D-Galactose is a specific stereoisomer of galactose.

Image summary: The image shows a chemical structure diagram. It depicts a six-membered ring with one oxygen atom within the ring. Several hydroxyl groups (-OH) are attached to the ring at various positions, along with a hydroxymethyl group (-CH2OH). Based on the structure, it is likely a representation of a simple sugar.

Other Monosaccharides

• Ribose

• Five carbon sugar

• Used in the formation of Ribonucleic acid (R.N.A.)

• Very little present in our diet

• Ribose is also found in the vitamin riboflavin and other biologically important molecules D-Ribose

Image summary: The image is a structural formula of a chemical compound. The compound is D-2-Deoxyribose. The structure shows a five-carbon chain with a carbonyl group at one end and a hydroxymethyl group at the other end. There are hydroxyl groups attached to three of the carbon atoms. The absence of a hydroxyl group at the second carbon is a distinguishing feature of deoxyribose compared to ribose.

• Deoxyribose

• Five carbon sugar

• Used in the formation of deoxyribonucleic acid (D.N.A.)

• Not considered a nutrient of our diet since our bodies can make all that it ever needs.

Image summary: The image is a structural formula diagram. It depicts the chemical structure of D-2-Deoxyribose. The structure shows a five-carbon sugar molecule, with a carbonyl group at the first carbon, and hydroxyl groups attached to the third and fourth carbons. The absence of an oxygen atom on the second carbon is a notable feature.

Other Monosaccharides - mannose

• Mannose is a monosaccharide found most notably in cranberries.

• It is not easily absorbed by the body.

• Mannose is an epimer of glucose.

- Mannose has been shown to be effective against urinary tract infections (U.T.I.s).

• When the level of mannose builds up in the bladder, bacteria will attach themselves to the mannose in the urine and be eliminated.

Image summary: The image is a photograph. It depicts two wooden bowls filled with cranberries. The cranberries appear fresh and ready to eat, suggesting a focus on healthy eating or seasonal produce. The arrangement and lighting create an appealing image, likely intended to evoke feelings of abundance.

Image summary: The image is a structural formula diagram. It depicts a monosaccharide molecule in its open-chain form. The molecule contains an aldehyde functional group at one end and a primary alcohol group at the other end, with multiple hydroxyl groups attached to the carbon chain. Based on the structure, it can be inferred that the molecule is an aldose sugar, specifically a hexose due to the presence of six carbon atoms.

The Structural Differences between Glucose, Galactose, and Fructose

Definition

Hexose: A monosaccharide containing six carbon atoms.

Hexose sugars (C sub 6 H sub 12 O sub 6)

Glucose Galactose Fructose

Figure 4.2 summary: The figure shows chemical structures of monosaccharides. It includes both open chain and ring structures. The open chain structures represent glucose, galactose, and fructose, highlighting the position of the carbonyl group. The ring structures depict the cyclic forms of glucose, galactose and fructose. The arrangement of atoms and functional groups differs among the monosaccharides, leading to variations in their chemical properties.

The straight chain structure

Image summary: The image is a structural formula diagram. It shows the chemical structure of a monosaccharide. The molecule contains a carbonyl group (aldehyde) at the top, followed by a chain of carbon atoms, each bonded to a hydroxyl group, except for the terminal carbon, which is part of a hydroxymethyl group. This structure shows that the molecule is an aldose, a type of monosaccharide with an aldehyde functional group.

Cyclization

• Less than 1% of C.H.O. exist in an open chain form.

• Predominantly found in ring form.

• The predominant forms of the monosaccharides (e.g. glucose, fructose, galactose, ribose) and many other sugars in solution are not in the open chains.

• Rather, the open chain forms of these sugars cyclize into rings because the ring forms are energetically more stable.

Cyclic Forms of Monosaccharides (Haworth Projection Formula)

• The basis for the ring formation is the fact that an aldehyde can react with an alcohol to form a hemiacetal.

• Similarly, a ketone can react with an alcohol to form a hemiketal.

• This involves reaction of C-5 O.H. group with the C-1 aldehyde group or C-2 keto group respectively.

Ring /cyclic structure (Haworth projection)

Image summary:The image is a chemical reaction diagram. It depicts two distinct reactions: the reaction of an aldehyde with an alcohol to form a hemiacetal, and the reaction of a ketone with an alcohol to form a hemiketal. Both reactions are shown as reversible, indicated by the presence of equilibrium arrows. The reactions indicate that aldehydes and ketones undergo a similar type of reaction with alcohols, leading to the formation of related but structurally different products.

Image summary: The image is a chemical structure diagram. It illustrates the Haworth projection formula of glucose. It depicts the transformation of D-Glucose from its open-chain form to a cyclic form, specifically alpha-D-Glucopyranose, via the Fisher structure. The conversion shows how the linear structure of glucose cyclizes to form a pyranose ring, which is a six-membered ring containing oxygen. The Haworth structure provides a more accurate representation of the three-dimensional arrangement of atoms in the cyclic form of glucose compared to the Fisher projection.

Haworth projection formula of fructose

Image summary: The image is a chemical structure diagram. It illustrates the conversion of D-Fructose from its open-chain form to its cyclic form, alpha-D-Fructofuranose. The diagram shows the transformation from the Fisher projection to the Haworth projection. The conversion involves the formation of a five-membered furanose ring. The diagram depicts how the linear form of fructose cyclizes to create a more stable ring structure.

Pyranose and Furanose forms

• After cyclization of glucose, the resulting six-membered oxygen containing ring is similar to pyran.

• A sugar with such a ring is called a pyranose eg. glucose.

• Similarly, the oxygen-bridge between the second and the fifth carbon atoms of fructose resembles a furan.

• A sugar containing such a ring is termed a furanose eg. fructose.

Definition

Furan and Pyran rings: Cyclic forms of monosaccharides. Furan rings are five-membered rings, while pyran rings are six-membered rings.

Furan and Pyran rings Although monosaccharides are often drawn as straight chains (Fischer projections), they exist mainly as ring structures in which the aldehyde or ketone group has reacted with a hydroxyl group in the same molecule.

Image summary:The image shows a chemical structure diagram. The diagram depicts a five-membered heterocyclic molecule. The molecule contains an oxygen atom at one vertex and two double bonds in the ring. The molecule is furan, a common aromatic heterocycle.

Image summary:The image shows a chemical structure diagram. It depicts a six-membered ring containing an oxygen atom as one of the vertices. The ring also features two double bonds. The presence of alternating single and double bonds suggests the possibility of resonance within the ring system, potentially influencing the molecule's stability and reactivity.

• Furanose and pyranose rings contain five and six members, respectively, and are usually drawn as Haworth projections.

• The hydroxyl group on the anomeric carbon may be in the alpha or beta configuration.

• In the a configuration, the hydroxyl group on the anomeric carbon is on the right in the Fischer projection and below the plane of the ring in the Haworth projection.

• In the beta configuration, it is on the left in the Fischer projection and above the plane in the Haworth projection

Image summary:The image is a chemical structure diagram. It depicts the interconversion of D-Glucose between its open-chain form and two cyclic forms: alpha-D-Glucopyranose and beta-D-Glucopyranose. The open-chain form of D-Glucose can cyclize to form either the alpha or beta anomer. The primary difference between the alpha and beta forms lies in the orientation of the hydroxyl group on the first carbon atom; it is oriented differently in each anomer.

Formation of alpha-& beta-D- glucose

Image summary: The image is a chemical structure diagram. It depicts the linear form of D-glucose and its two cyclic forms, alpha-D-glucose and beta-D-glucose. The diagram illustrates the structural formulas of these three forms of glucose, showing the arrangement of carbon, hydrogen, and oxygen atoms. The difference between alpha and beta forms lies in the orientation of the hydroxyl group on carbon number one, which has different positions.

Formation of alpha-& beta-D-

Image summary: The image is a chemical structure diagram. It depicts a molecule with a chain of carbon atoms, with hydroxyl groups and hydrogen atoms attached to the carbons. The diagram also shows an intramolecular reaction, where a hydroxyl group reacts with a carbonyl group to form a cyclic structure. This suggests the molecule can exist in both linear and cyclic forms.

Image summary:The image shows chemical structure diagrams. The diagrams depict the structures of alpha-fructose and beta-fructose. The primary variance between these structures lies in the orientation of the hydroxyl group and hydroxymethyl group attached to the carbon on the right side of the ring. In alpha-fructose, the hydroxyl group is oriented upwards, while in beta-fructose, the hydroxymethyl group is oriented upwards.

Definition

Ketohexoses: A hexose sugar containing a ketone group.

For ketohexoses, the C-2 keto group reacts with the –O.H. on C-5 to form an intramolecular hemiketal. (the oxygen in the ring is from –O.H. from From C-5). For the beta-form, the –O.H. on C-2 is upwards).

Anomeric carbon, Asymmetric carbon atom (chiral carbon):

• It is that carbon atom attached to four different groups or atoms.

• Formation of a ring results in the creation of an anomeric carbon at carbon 1 of an aldose or at carbon 2 of a ketose.

Image summary:The image is a diagram showing the chemical structures of D-Glucose and D-Fructose, along with their cyclic forms, alpha-D-Glucopyranose and alpha-D-Fructofuranose. The diagram illustrates the transformation from the open-chain form of each sugar to its respective cyclic form. The structures highlight the difference in the position of the carbonyl group (aldehyde in glucose, ketone in fructose) and how this leads to different ring structures upon cyclization. Glucose forms a six-membered ring (pyranose), while fructose forms a five-membered ring (furanose).

Anomeric carbon in glucose

Image summary: The image shows a structural formula of a cyclic sugar. The formula depicts the arrangement of carbon, hydrogen, and oxygen atoms within the sugar molecule. The structure highlights a specific carbon atom, referred to as the anomeric carbon, which is a key feature in determining the sugar's isomeric form. The alpha and beta forms of sugars are called anomers.

Isomerism

Definition

Isomers: Molecules that have the same molecular formula but different structural arrangements.

The compounds possessing same molecular formula and different structures are referred as Isomers.

The phenomenon of existence of isomer is called Isomerism.

Definition

Stereoisomerism: A type of isomerism in which molecules have the same structural formula but differ in the spatial arrangement of atoms.

Structural Isomerism Stereoisomerism

Structural Isomerism

same molecular formulae but differ in their structures.

Aldose-Ketose Isomerism Glucose and fructose isomers of each other. ▶ They are having same molecular formula C sub 6 H sub 12 O sub 6 ➔ But differ in their structural formula.

Aldose-Ketose Isomerism

Math summary: This expression represents the chemical formula for a molecule. It indicates the types and quantities of atoms present in the molecule.

Image summary: The image is a chemical structure diagram. The diagram shows two different chemical structures that are similar. Both structures have a chain of carbons with alcohol groups attached, but they differ in the location of the carbonyl group. One structure has the carbonyl group at the end of the chain, while the other has it in the middle. The first structure is an aldose sugar, and the second structure is a ketose sugar.

D - Glucose D - Fructose

Stereoisomerism

implies same molecular formula, structures but differ in their configuration.

Asymmetric (Chirl) carbon allow the formation of stereoisomerism.

Types of stereoisomerism of glucose are.....

Table summary: The table presents a list of different types of isomerism.

Asymmetric or Chiral Carbon Centres

• Note: An asymmetric carbon atom has four different chemical groups attached to it.

• Calculation of no of asymmetric centres

• The number of asymmetric centres or chiral carbons determine the possible no of steroisomers and can be calculated

using the vant Hoffs rule 2n ie 2 raised to the power n : where n denotes the no of asymmetric centres . Hence for glucose with 4 chiral carbons ,the possible no of stereoisomers would be 2x2x2x2= 16.

Stereoisomers, enantiomers, and epimers

• Stereoisomers have the same chemical formula but differ in the position of the hydroxyl groups on one or more of their asymmetric carbons.

• Enantiomers are stereoisomers that are non superimposable mirror images of each other.

• They differ in configuration at all chiral centers. All chiral centres are opposite.

• They have identical physical properties (except optical rotation)

• Example: D-glucose and L-glucose

D and L isomerism (enantiomer)

Image summary:The image shows chemical structure diagrams. It depicts the structures of D-Glyceraldehyde, L-Glyceraldehyde, D-Glucose and L-Glucose. The structures differ based on the arrangement of hydrogen and hydroxyl groups around the carbon atoms. D and L isomers are mirror images of each other, differing in the spatial arrangement of atoms around a chiral center.

D and L isomerism (enantiomer)

D and L isomers are mirror images of each other.

Definition

Enantiomers: Stereoisomers that are non-superimposable mirror images of each other.

These two forms are called Enantiomers.

Image summary:The image is a structural diagram. It illustrates two different forms of glucose molecules. The diagram presents the chemical structures of D-glucose and L-glucose, showing the arrangement of carbon, hydrogen, and oxygen atoms. The two glucose forms are mirror images of each other, differing in the spatial arrangement of atoms around a chiral carbon center. This difference leads to distinct chemical properties and biological activities.

The D and L Forms of Monosaccharides

Image summary: The image presents chemical structure diagrams. The diagrams depict the molecular structures of D-Glyceraldehyde, L-Glyceraldehyde, D-Glucose, and L-Glucose. The primary structural difference between the D and L forms of both Glyceraldehyde and Glucose lies in the spatial arrangement of atoms around a specific chiral center. Specifically, the position of the hydroxyl group is different in D versus L isomers.

• For linear carbohydrates, common types of stereoisomers include enantiomers, diastereomers, and epimers.

• In cyclic carbohydrates, the main stereoisomers are anomers.

• Anomers are stereoisomers that only differ in the configurations of groups around the anomeric carbon, which is the carbon that loses its double bond to oxygen and becomes chiral during intramolecular reactions.

Diastereomers

- Diastereomers are defined as compounds with the same molecular formula and sequence of bonded elements but are non-superimposable non-mirror images.

• Diastereomers only occur in compounds containing more than one chiral center. They differ at one or more -but not all-chiral centers.

• In a pair of diastereomers, some of the chiral centers are the same in the two molecules, but others are different.

• Diastereomers are stereoisomers that are not mirror images of each other.

• Diastereomers often have different physical properties, such as melting points, boiling points, and solubilities.

• D-Glucose and D-Galactose are diastereomers

Image summary: The image shows chemical structure diagrams. It depicts the structures of L-glucose, D-glucose and D-galactose. L-glucose and D-glucose are enantiomers, while D-glucose and D-galactose are diastereomers. The structures differ in the arrangement of hydroxyl and hydrogen groups around the chiral carbons.

Epimerism

• Epimers are sugars which differ from each other with respect to single carbon other than the anomeric carbon.

• Galactose and Mannose are the epimers of glucose

• They differ from glucose with respect to C-4 and C-2 respectively.

• Epimers are stereoisomers that differ in the position of the hydroxyl group at only one asymmetric carbon.

• For example, D-glucose and D-galactose are epimers that differ at carbon 4 -see later.

Epimers of glucose

Image summary:The image is a structural formula. The formula depicts a carbohydrate molecule. The molecule contains an aldehyde group at the top, followed by several chiral carbons with hydroxyl groups attached, and a primary alcohol group at the bottom.

Image summary: The image shows a structural formula of a carbohydrate. The structure consists of a carbon chain with an aldehyde group at one end and an alcohol group at each of the other carbons. The structure indicates the substance is a monosaccharide, more specifically, an aldose due to the presence of the aldehyde group.

Image summary: The image is a structural formula diagram. The diagram depicts an organic molecule with a chain of carbon atoms. The molecule contains an aldehyde group at one end and a hydroxyl group at the other end of the carbon chain. The molecule is a monosaccharide, specifically an aldose sugar.

D - Galactose D - Glucose D - Mannose

Anomerism

In solution glucose predominantly exist as closed chain structure.

Because of cyclization of sugar, an additional asymmetric center is created at C-1 (anomeric carbon).

This leads to formation of two isomers namely....

- ➔ a-D-glucopyranose

- ☑ beta-D-glucopyranose

Anomeric carbon in glucose

Image summary:The image is a structural diagram of a chemical compound. The diagram shows the structure of alpha-D-Glucopyranose. The diagram highlights the anomeric carbon, which is a specific carbon atom within the ring structure. The structure indicates the arrangement of atoms and bonds within the molecule, providing information about its chemical properties and potential interactions.

Definition

Anomers: Cyclic stereoisomers that differ only in the configuration at the anomeric carbon.

Formation of alpha and beta-D- glucose note: alpha and beta forms of sugars are therefore called Anomers

Image summary: The image is a chemical structure diagram. It illustrates the linear form of D-glucose and its conversion to two cyclic forms, alpha-D-glucose and beta-D-glucose. The diagram highlights how the linear form cyclizes to create two different isomers. The difference between the alpha and beta forms is the position of the hydroxyl group on carbon number one; it is oriented differently in each isomer.

• The two stereoisomers at the hemiacetal (anomeric) carbon are:

• The alpha anomer: Where-O.H. group is down (Haworth)

• The beta anomer: Where-O.H. group is up (Haworth)

• Anomers are diastereomers (having different physical properties)

Optical Isomerism

• When a plane polarized light is passed through a solution containing monosaccharides the light will either be rotated towards right or left.

• This rotation is because of the presence of asymmetric carbon atom.

• If it is rotated towards left-levorotatory (-) and If it is rotated towards right-dextrorotatory(+)

Image summary: The image is a schematic diagram illustrating the rotation of polarized light by a solution of an enantiomer. Unpolarized light, which vibrates in all planes, passes through a polarized lens, resulting in plane-polarized light. This polarized light then enters a tube containing a solution of an enantiomer, which rotates the plane of polarization. The exiting light is still polarized, but its plane of polarization is different from the original polarized light, demonstrating the optical activity of the enantiomer.

• When equal amounts of dextrorotatory and laevorotatory isomers are present, the resulting mixture

• has no optical activity, since the activities of each isomer cancels each other. Such a mixture is said to be Racemic.

Mutarotation

• Unlike the other stereoisomeric forms, alpha and beta anomers spontaneously interconvert in solution.

• This is called mutarotation.

Image summary:The image is a chemical structure diagram that illustrates the transformation of a molecule. The diagram depicts a cyclic structure with several hydroxyl groups attached. The transformation involves a change in the orientation of one of the hydroxyl groups on the ring. The initial structure has a specific orientation of the hydroxyl group, and the transformation results in a different orientation of the same hydroxyl group.

Mutarotation

• Mutarotation is defined as a change in the specific rotation of plane polarized light by a substance.

• Is measured in degrees.

• Concept can be illustrated with glucose.

• A freshly prepared aqueous solution of a-D-glucose has an optical rotation of +112.2°

A similar solution of beta-D-glucose has an optical rotation of plus 18.7 degrees

Mutarotation

• On standing:

- a-D-glucose changes from +112.2° to +52.7° (decrease)

- beta-D-glucose changes plus 18.7 degrees to plus 52.7 degrees (increase)

- – This change in optical rotation is called mutarotation.

- – At this specific rotation of plus 52.7 degrees (equilibrium), there is a mixture of 36% of alpha-D-glucose and 64% of beta-D-glucose.

- – The change is due to the transformation of a form to beta form and beta form to a form (interconversion)

- – The process involves the opening of the ring structures

- – Mutarotation is a characteristic feature of Reducing sugars.

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