Definition of Carbohydrates


Carbohydrates form the third largest group of organic molecules found in living things. It is formed by the formation of C, H and O elements according to the formula Cn(H2O)n. However, there are also compounds that are not carbohydrates (such as Acetic acid C2H4O2; Lactic Acid - C3H6O3;) although they comply with this general formula, or are carbohydrates (Deoxyribose - C5H10O4; Rhamnose - C6H12O5), although they do not comply with the general formula. Some carbohydrates containing nitrogen and sulfur also do not fit this general formula. Carbohydrates, aldehyde or ketone derivatives (monosaccharides) of polyhydroxylic alcohols, their polymers (oligo- and polysaccharides), oxidation products (sugar acids), reduction products (sugar alcohols), substitutions (amino sugars) and esters (sulfated or phosphated esters)' is

The Importance of Carbohydrates

Carbohydrates are used for a wide variety of purposes in living things. It is one of the most important energy sources of animals in the form of glucose and glycogen. Starch formed by photosynthesis in plants is stored and plays a role as an energy source. It participates in the structure of the protective cell wall of microorganisms in the form of polymers. Cellulose is the most important extracellular structural component of the woody and fibrillar tissues of plants and the rigid cell wall. As a result of the metabolism of glucose, intermediate metabolites appear, which are used as precursors in the biosynthesis of many biological molecules. Simple sugars form nucleic acids by binding to purines, pyrimidines and phosphates, peptidoglycans by binding to peptides, glycolipids by binding to lipids, mucopolysaccharides by binding to sulfates, and derivative carbohydrates by binding to other substances.

Classification of Carbohydrates

Carbohydrates can be classified in different ways.

1. According to the number of simple sugar units in the molecule

  • Monosaccharides
  • Disaccharides and Oligosaccharides
  • Polysaccharides

2. According to the reagent groups:

  • Aldoses
  • ketoses

3. According to the length of the carbon chain:

  • dioses
  • pentoses
  • trioses
  • hegsose
  • Tetroses
  • heptoses

Here, carbohydrates were examined in four groups according to the number of simple sugars in the molecule.

  1. Monosaccharides
  2. Derivative monosaccharides
  3. Disaccharides
  4. polysaccharides

Monosaccharides have low molecular weight and are represented as hydrates of carbon with n 2-3 in the general formula (CH9O)n. Derivative monosaccharides are derivatives of monosaccharides. They contain functional groups other than or in addition to carbonyl and hydroxyl groups. Oligosaccharides and polysaccharides consist of the condensation of monosaccharide residues with acetal bonds to form a large compound. The simplest oligosaccharide is composed of two monosaccharides and is called a disaccharide. Those formed from three, four, and five monosaccharides are called tri-, tetra-, and pentasaccharides, respectively. Polysaccharides are polymers with high molecular weights formed by the condensation of many single type monosaccharides (homopolysaccharides) or two or more different types of monosaccharides (heteropolysaccharides).

1 – Monosaccharides

In the structure of monosaccharides, aldehyde (-COH) or ketone (-C-O-) group (which is also called carbonyl group or active sugar group) on the first carbon of a carbon skeleton and a large amount of hydroxyl groups are added in the rest of the skeleton. is found. A monosaccharide with an aldehyde group is called aldose, and a ketone group is called ketose.

The simplest monosaccharides are glyceraldehyde and dihydroxyacetone. Almost all simple sugars are derived from these two main structures.

A carbon atom with four separate atoms or groups of atoms attached to its four valences is called an asymmetric carbon atom. Glyceraldehyde has one asymmetric carbon atom. This is the second carbon atom.

The arrangement of -H and -OH attached to this carbon atom according to the mirror image in space is in two ways. According to these sequences, glyceraldehyde is called D- and L-glyceraldehyde.

Simple sugars whose hydroxyl group is in the same direction as D-glyceraldehyde are added with D-, and those with L-glyceraldehyde in the same direction are added L-. Glyceraldehyde is considered the reference compound for the determination of the D- and L-forms of all stereoisomeric compounds.

Glyceraldehyde and dihydroxyacetone are three-carbon monosaccharides. These are called trioses. Glyceraldehyde (D or L), a triose sugar, is also an aldose. Therefore, it is also called aldotrioz for short. Dihydroxy acetone is a ketotriose. Names indicate only significant functional groups, as well as the number of carbon atoms.

The generic names of aldoses indicate the number of carbon atoms in the molecule. Accordingly, tetroses, pentoses, hexoses, heptoses, octoses and nanoses contain four, five, six, seven, eight and nine carbon atoms, respectively. The classification names of ketoses are established by putting the syllable "ul" in the names of the aldoses corresponding to ketosis. For example, pentulose, hexulose and heptulose.


Substances that show stereoisomerism are substances that are in the mirror image of each other in space. The atoms or groups of atoms they have are similar to each other. But these are not the same substances. A molecule can show two kinds of isomerism, depending on the positions of the atoms in space. This is called stereoisomerism, optical isomerism, or geometric isomerism.

Glucose, galactose, and mannose are six-carbon monosaccharides. They carry an aldehyde group. The closed formulas are the same. But these monosaccharides are different aldohexoses from each other. This is due to the configuration of the groups that make up the molecule. These compounds, which have the same closed formula but differ due to the asymmetric carbon atom they carry, are called geometric isomers, stereoisomers or enantiomorphs.

Optical isomers of sugars with different configurations of groups attached to only one carbon atom are also called epimers. The groups of sugars at other carbon atoms are exactly the same. Such sugars are called epimer sugars. These sugars are easily converted to each other by the enzyme called epimerase in the liver of animals. This phenomenon is called epimerization. Glucose and galactose and glucose and mannose are epimer sugars.

An aldotetrose has two asymmetric carbon atoms, and an aldopentose has three asymmetric carbon atoms. Aldohexose has 4 asymmetric carbon atoms. If a compound has n asymmetric carbon atoms, according to Van't Hoff's formula, this compound has as many as 2n stereoisomers. Accordingly, since glucose, an aldohexose, has 4 asymmetric carbon atoms, it has 24 stereoisomers, ie 2x2x2x2=16.

Numbering of Carbon Atoms D- and L-Identification

Sugars are numbered starting from the carbon atom containing the aldehyde or ketone group. Accordingly, the number one carbon atom is at the top in straight formulas; the other atoms are numbered sequentially accordingly. The alcohol (-OH) group on the last carbon atom is also called the primary alcohol group. Since these formulas were introduced by Emil Fischer, this form of representation is called Fischer projections.

In denoting the configuration of any monosaccharide with D- and L-, for aldoses, look at the center of asymmetry farthest from the end of the molecule with the aldehyde group. This center is the 5th carbon atom in hexoses. If the configuration at this carbon atom is similar to the configuration of the asymmetric carbon atom in D-glyceraldehyde, that monosaccharide is included in the D-series, if it is similar to the asymmetric carbon atom in L-glyceraldehyde, it is included in the L-series.

Optical Activity

If ordinary light is passed through a Nikol prism, a polarized light plane is obtained. Polarized light is light that fluctuates in just one plane. Substances containing asymmetric carbon atoms have the ability to turn polarized light to the right or left. For this reason, these substances are also called optical active substances. Those that deflect the polarized light plane to the right are called dextrorotators, and those that deflect it to the left are called Levorotators. We noted earlier that the use of D and L is based on differences in configuration between monosaccharides. However, if the optical rotation sign of a specific monosaccharide is included in the nomenclature of its compound, then the rotation is denoted by "d" and "l" in italics, or by the sign (+) and (-).

Because they are optically active, glucose, galactose and mannose are also optical isomers. By making use of these properties of sugars, the amount of sugar can be determined in special instruments called polarimeters. The only physicochemical difference between optical isomers is that they reverse the plane of polarized light.


The degrees of conversion of sugars to polarized light are expressed as specific conversions. The degree of flipping the plane of polarized light depends on the type of compound, the concentration of sugar, the wavelength of the light, the length of the light path, the type of solvent and its temperature. Some of these factors can be fixed in instruments that measure specific degrees of rotation, called polarimeters. Accordingly, the specific degree of inversion means the degree to which a substance (sugar) turns polarized light when a solution of 100 grams per 100 ml (ie, a solution containing 1 gram of optical active substance per milliliter) is in a 1 dm tube. The specific degree of rotation is calculated according to the formula.

Here a - the angle of rotation, C - the gram concentration of sugar in 100 ml, L - the length of the tube in which the solution is placed in decimeters. If the type of sugar is known, the concentration can be calculated from this formula. D20, on the other hand, gives information about the wavelength state of the light at 20 C. As a light source, a light with a wavelength of 589.3 nm with a sodium lamp or a light with a wavelength of 546.1 nm with a mercury vapor lamp is used. D relates to the sodium lamp.

Specific degrees of conversion of some carbohydrates at 20 oC D-glucose +52.7, D-fructose -92.4, D-galactose +80.2, L-arabinose +104.5, D-mannose +14.2, D-arabinose -105.0, D-Xylose + 18.8, Lactose +55.4, Sucrose +66.5, Maltose +130.4, Invert sugar -19.8, Dextrin +195.

Ring Structures of Aldoses and Ketoses

If the aldehyde combines with an alcohol molecule, the resulting product is a "hemiacetal". Like hemiacetals, there are also "hemiketals". This time the reaction takes place between the ketone group and the alcohol group.

In hemiacetals formed by sugars, the aldehyde group of the sugar forms the aldehyde, and the alcohol is the rest of the molecule. It is an intramolecular hemiacetal. On the other hand, hemiketals have a ketone group instead of an aldehyde group.

When monosaccharides are dissolved in water, the groups that react to form a hemiacetal structure (carbonyl groups and alcohol groups) form a cyclic structure because they are in the same molecule. If carbon atoms one and five are joined by an oxygen bridge, they appear as a six-atom ring. Sugars with such a ring are called pyranoses. The reason for this name is that they resemble a piran ring. Aldoses with this type of ring are called aldopyranoses. Accordingly, alpha-D-glucose and Beta-D-glucose can be represented as alpha-D-glucopyranose and Beta-D-glucopyranose, respectively.

If a pentagonal ring structure is formed, this ring is called furan ring and sugars with furan ring structure are called furanoses. Aldoses also exist largely in the form of a furan-like, durable 5-atom ring and are considered aldofuranoses. Pentatomic rings are common among aldopentoses and are found as such in oligosaccharides. Thus, Beta-D-arabinose can be named as Beta-D-arabino furanose and Beta-D-ribose as Beta-D-ribofuranose. Ketohexoses also form stable 5-atom rings. For this, Beta-D-fructose is Beta-D-fructofuranose.

Pentoses can form pyranose or furanose rings as well as longer chain aldoses and ketoses.

Linear structures proposed by Fisher facilitate the separation of different stereoisomers of monosaccharides. Many sugars do not show an additional center of asymmetry. To explain the cyclic structure of pyranoses and furanoses, they are often written as hexagons or pentagons. These are also called Haworth projections.

In practice, the suffixes pyranose and furanose, which indicate the ring structures at the end of the names of sugars, are not used much.


When the freshly prepared glucose solution is examined in a polarimeter, it is observed that the optical rotation is not constant, it changes over time, the change stops after a certain time and the angle becomes constant. Other sugars also show this behavior. This phenomenon is called mutarotation, that is, rotational change.

When monosaccharides are dissolved in water, the groups that react to form a hemiacetal structure (carbonyl groups and alcohol groups) form a cyclic structure because they are in the same molecule. When a monosaccharide takes the form of a hemiacetal, the number one carbon atom also becomes asymmetrical. In mutarotation, glucose, which was in a single form before being dissolved, forms ring structures in solution after it is dissolved, and accordingly, the rotation angles are changed.

The number one carbon atom that becomes asymmetrical with the hemiacetal structure of a monosaccharide is called the anomeric carbon. Aldoses separated from each other only by the configuration at the anomeric carbon atoms are called anomers. The two D-Glucose isomers formed at the end of the solution of glucose in water are also called anomers. These anomeric shapes are divided into a (alpha) and b (beta). These stereoisomers are alpha-D-glucose and beta-D-glucose, which produce mutarotation. Mutarotation is the basis of the reciprocal alternation of alpha and beta forms by forming an open-chain aldehyde or its hydrate as an intermediate. In the mixture of anomers formed at the end of mutarotation, there is 33% aD-Glucose and 67% bD-Glucose.

The specific degree of rotation of aD-Glucose is + 112.2, while the specific degree of rotation of bD-Glucose is + 18.7. As a result of mutarotation, different degrees occur until an equilibrium is established in the aqueous solution, an equilibrium is reached over time, and the optical rotation degree in equilibrium becomes +52.7.

According to Van't Hoff's formula, by Fischer projection, glucose 24 has 16 stereoisomers. In each of the alpha-D-glucose and beta-D-glucose formulas, 5 centers of asymmetry and thus 25 32 isomers are possible. Every aldose is suitable for alpha and beta modifications. The alpha shape is used in flat projection to show that the hydroxyl group at C-1 is on the same side as the oxygen atom in the structure of the ring; In the beta modification, it shows that the hydroxyl group in C-XNUMX is on the opposite side of the oxygen atom in the ring structure. Among sugars with the D-configuration, alpha isomers always have more positive optical rotation than beta isomers. In the L-series, that is, in the mirror images of the D structures shown above, the anomer with more negative rotation is the alpha anomer.


It is not possible to represent the true shape of molecules on a plane. Therefore, the model proposed by Haworth makes it easier to draw the structures of sugars and provides clarity in showing the configurations. Although the Fischer formula is an abnormal structure that does not fit the truth because it extends the oxygen-carbon bond too long, the distance between atoms in the Haworth formula is proportional to each other and closer to the truth. However, it is not always used because it is difficult to draw.

In the Haworth formulation, the ring comes perpendicular to the outside of the paper plane, and the groups attached to the carbon atoms in the ring are located on the lower and upper surfaces of the ring plane. Bold lines in the formula are near the reader.

In reality, the atoms that make up the ring do not lie on a plane. Because the annular structure is not a rigid structure, it has the opportunity to bend and bend in aqueous solutions. The two conformations most likely to formulate are chair and rowboat forms. Chair shapes with equatorially oriented hydroxyl groups are considered to be more stable than boat shapes. There is a weak correlation between the chair-shaped structures parallel to the axis of symmetry and the equatorial axis. On the other hand, this relationship is stronger in sugars with boat-shaped formula structure.

Furanoses have a variety of conformations. Often an atom has risen above the plane.

Reactions of Monosaccharides with Acids and Bases

Dilute base solutions cause new arrangements around the anomeric carbon atom and the adjacent carbon atom of momosaccharides at room temperature. Enediol intermediate structure is formed. If D-glucose is treated with dilute alkalis, an equilibrium mixture of D-glucose, D-Fructose and D-mannose is formed. This transformation is called the “Lobry de Bruyn-Alberta van Eckenstein” transformation.

Strong mineral acids convert sugars to methyl, ethyl and hydroxy furfural derivatives. These derivatives combine with various polyphenols to give colored products. Their color and spectroscopic properties are related to the polyphenol and sugar used. Therefore, the reactions (Molisch, Seliwanoff, and Bial) serve to demonstrate the presence of different types of sugars.


If the yellow ozone crystals formed by various sugars with phenylhydrazine are examined under a microscope, it is seen that most of them are in different shapes. All alpha-hydroxy carbonyl compounds react with phenylhydrazine to form ozone. The initial reaction is the coupling of the carbonyl group with phenylhydrazine. Subsequently, the alpha-hydroxy group is oxidized to a carbonyl group. This carbonyl group then combines with another phenylhydrazine molecule.

Ozazone formation disrupts the configuration of the 1st and 2nd carbon atoms. For this reason, sugars (for example, glucose, fructose and mannose) that differ from each other only by having different configurations at the 1st and 2nd carbon atoms give the same ozone. In addition, the ozone delivery times of sugars are different. For this reason, determining the time taken for the formation of ozone crystals is especially important in recognizing sugars that are close to each other that make up the same ozone. All of the reducing sugars form phenylhydrazine and ozone. So, sucrose does not give ozone. Glucose does not give ozone upon heating with phenylhydrazine hydrochloride, the reaction only takes place in the presence of acetic acid.

Ozazone Experiment

0.2 ml of 3% solutions of glucose, fructose, maltose and lactose into four test tubes, respectively. is taken. 3 ml each. A freshly prepared reagent (a mixture of phenylhydrazine + hydrochloride + sodium acetate + acetic acid) is added. The tubes are mixed and placed in a boiling water bath. It is kept in this way until a large number of yellow crystals appear. The crystallized tube is removed from the water bath and allowed to cool in a tube carrier (not under tap water).

Meanwhile, the crystallization time for each sugar is also recorded. As it cools, the crystals condense (ozazon). With the help of a pipette, some of these crystals are taken on the microscope slide and examined under the microscope. Shapes of crystals are drawn. Glucose and fructose give crystals quickly and the shape of the crystals formed is the same and in the form of crop bundles. Lactose and maltose give ozone crystals in a much longer time (about 30 minutes). Lactozazone crystallizes in the form of irregular fine needles (horse chestnut) formed at 100 degrees Celsius. Maltozazone crystallizes in the form of large tablets formed at 206 degrees Celsius (sunflower)

Glucosazone x 250

The photo of the glucazozone you see above taken from the source. You can also see photos of x 250 ozone crystals of maltose, galactose and lactose at the same address.

Click here to see the ozone crystals given by other sugars.

Biologically Important Monosaccharides

Only glucose and fructose are abundant in nature. Some other monosaccharides are common either as units in disaccharides and polysaccharides or some other type of compound. Usually this is aldohexoses such as hexoses glucose, mannose and galactose and ketohexose such as fructose, which exist in the form of compounds.

Glucose and mannose are epimers at carbon number 2 (different by the configuration of a single carbon atom). Glucose and galactose form an epimeric pair with respect to carbon number 4. The fructose anomeric carbon atom differs from the others in that it is the 1nd carbon atom instead of the 2st carbon. However, it is identical with fructose, glucose and mannose in terms of the configurations of carbon atoms 3, 4 and 5.

D-Glucose is an aldohexose. It is also called dextrose because it is a dextrorotator. It participates in the structure of many important disaccharides and polysaccharides. It is also called grape sugar because it is abundant in grapes. It is sweet and delicious. It is very important from a biochemical point of view.

D-Galactose is rarely found free in nature. It is the building block of lactose. It is also involved in the structure of cerebrosides, gangliosides and glycoproteins. L-Galactose is found in agar, a polysaccharide obtained from algae. It tastes less than glucose. In terms of fermentation, it is fermented more slowly by yeasts compared to glucose.

D-Fructose is a ketohexose and is called levulose because of its levorotatory properties. It is the building block of sackarasun and inulin. It is common in plants. It is also found in honey. There is free fructose in fetal blood, placenta and semen. It participates in the structure of raffinose, a trisaccharide.

D-Mannose is found in plants partly free and partly bound. It is frequently encountered as the building block of glycopeptides and blood group substances in animal organisms.

Among the pentoses found in nature, there are aldoses such as L-arabinose, D-ribose and D-xylose, and L-xylulose, which is ketopentose. Alpha-D-xylulose forms a pyranose ring, which is very similar to glucose in other respects, except for the hydroxymethyl group attached to carbon 5 of glucose.

D-Ribose is found in the structure of ribonucleic acids and nucleotides that act as coenzymes.

D-Arabinose is the building block of gum arabic. It is found in plants.

D-Xylose Found in wood gums, proteoglycans. It participates in the structure of xylan found in the structure of straw and wood. This sugar is the keto anti-sugar D-xylulose. D-xylulose is an important intermediate in the uronic acid pathway.

If the taste of tea sugar (sucrose) is accepted as 100%, fructose 173%, glucose 74%, maltose 33%, galactose 33% and lactose 16% sweeter than sucrose.

2 – Derivative Monosaccharides

Sugar Acids

They are oxidation products of monosaccharides. The most well-known compounds in this group are formed by the oxidation of the aldehyde carbon at C-1, the hydroxymethyl carbon at C-6, or both, to the carboxyl group of aldoses. In other words, three types of sugar acids appear with the oxidation of aldoses.

  • Aldonic acids are formed by the conversion of the aldehyde group of aldoses to a carboxyl group.
  • By oxidation of the primary alcohol group to the carboxyl group, uronic acids are formed.
  • Aldaric acids are formed by the conversion of both the aldehyde group and the primary alcohol group to the carboxyl group.

If aldoses react with weak oxidizing agents, the carbonyl group is oxidized and aldonic acids are formed. These compounds are strong acids, their salts dissolve in water and give neutral solutions. Gluconic acid, which is formed from glucose in this way, is of biochemical importance. Likewise, mannoic acid is formed from mannose and galactonic acid is formed from galactose. Gluconic acids are non-toxic and well metabolized, often used to deliver a cation such as Ca2+ to the body.

Uronic acids, which are sugar acids in the second group, are of great biological importance. In these compounds, only the primary hydroxyl group is oxidized to the carboxyl group. In this way, oxidation of glucose produces glucuronic acid, oxidation of mannose produces mannuronic acid, and oxidation of galactose produces galacturonic acid. The most important uronic acid is glucuronic acid and is related to detoxification events. Glucuronic acid forms glycosides and is found in the urine bound by glycosidic bonds to various hydroxyl compounds such as phenols and steroids. The increase in water solubility of these alcohols due to the glycoside-uronic acid formation allows them to be easily excreted by the body. Glucuronic acid can form esters, as with bilirubin, a bile colored substance. It is also a component of many polysaccharides.

If aldoses are oxidized with stronger agents, both the aldehyde group and the 6th carbon atom are oxidized to carboxyl groups and aldaric acids (saccharic acids) are formed. Aldaric acids have no biological significance.

A sugar acid of biological importance, widely distributed in the animal and plant kingdoms, is ascorbic acid.

The oxidation of ketoses is not easy, as is the case with aldoses. If they are oxidized, they give products with fewer carbon atoms. For example, erythronic acid and glycocholic acid are formed from fructose.

Sugar Alcohols

The reduction of aldoses and ketoses forms sugar alcohols. However, while one type of alcohol is formed from aldoses, two types of alcohol are formed in the reduction of ketoses. Because a new asymmetric carbon atom is formed during the reduction of ketoses. Sorbitol is formed from glucose and mannitol is formed from mannose as reduction products. Fructose consists of both sorbitol and mannitol.

Two of the sugar alcohols are found abundantly in nature. The first of these is glycerol, which is formed by the reduction of glyceraldehyde, a triose sugar, to alcohol. The other is inositol, a cyclohexane derivative that becomes fully hydroxylated. Myoinositol, a stereoisomer of inositols, both enters the structure of lipids as phosphatidylinositol and participates in the structure of phytic acid as hexaphosphoric ester.

D-sorbitol acts as an intermediate for the synthesis of fructose in the prostate gland and is sometimes given to patients with diabetes as a sugar substitute. L-sorbose is also used in industry in the production of ascorbic acid.

Mannitol is used as an osmotic diuretic Glycerol is used as a humectant and can be nitrated to nitroglycerin Sorbitol can be dehydrated to tetrahydropyrans and tetrahydrofuran compounds (sorbitans) Sorbitans are converted to detergents known as spans and tweens (used in emulsification procedures) Sorbitol 1,4,3,6 can also be dehydrated to tetrahydropyrans (sorbitans) ed to ISDN and ISMN (both used in treatment of angina)

Mannitol, like xylitol and sorbitol, is a carbohydrate alcohol. It has a pleasant taste, maintains its stable structure in humid environments and does not lose color at high temperatures. For this reason, mannitol is frequently used in pharmacy and some nutritional tablets. Mannitol, which has anti-caking and bulking properties, is used as a low-calorie sweetener. It is tooth friendly. It is only absorbed in the small intestine and cannot be metabolized. Colonic bacteria in the lower parts of the digestive system metabolize the non-absorbed part. This causes soft stools in some people and gas formation in the intestines, as is the case with complex carbohydrates.

Unlike sorbitol, mannitol is not hygroscopic. For this reason, powdered mannitol is used in chewing gum production to prevent the chewing gum from sticking to the production machine. Mannitol is clinically used for treatment in head traumas. It destroys the brain-blood barrier and is therefore used to make many drugs related to the brain (eg Alzheimer's disease). Mannitol increases the secretion of water and sodium, thus reducing the extracellular fluid volume. Diabetics use it as a food sweetener. Mannitol is used in confectionery. Mannitol has a special effect on the renal vessels when the blood flow to the kidneys is reduced, restoring the function in a short time and therefore has a diuretic effect. It acts as a laxative (laxative) in excessive doses above 20 grams and is sometimes used for this effect in children.

Sugar Phosphates

Esterification of monosaccharides with phosphoric acid is very important for metabolic reactions. Ex. Important events such as glycogenesis occur only when glucose combines with phosphoric acid. If the OH group at carbon number one of glucose is esterified with phosphoric acid (H3PO4), Glucose-1-phosphate (G-1-P)(Cori ester), if esterified from carbon number 6, Glucose-6-phosphate (G-6-P) (Robinson ester) ) similarly, fructose-6-phosphate (F-6-P) (Neuberg ester) and Fructose 1,6 diphosphate (F-1,6-P) (Harden Young ester) occur from fructose.

The formation of phosphate derivatives of sugars in cells is called phosphorylation. There are special enzymes and coenzymes for these reactions.

Deoxy Sugars

These sugars are compounds with hydrogen instead of one or more hydroxyl groups in the pyranose and furanose rings. In other words, they are sugars that do not have oxygen in their 2nd or 6th carbon atoms. 2-deoxyribose is a component of the repeating unit in polymeric deoxyribonucleic acid. In these types of deoxy sugars, the terminal CH2OH group is replaced by the CH3 group. L-Rhamnose (6-deoxy-L-mannose) and L-fucose (6-deoxy-L-galactose) are among several sugars of the L-configuration found in plants and animals.

Amino Sugars

Amino sugars are important substitution products of monosaccharides. It is formed by the replacement of the hydroxyl group on the second carbon atom of the hexos with the NH2 group.

Glucosamine is formed by the insertion of an amino group into the 2nd carbon atom of glucose. For this reason, it is also called 2-desoxy,2-aminoglucose. It is found in various mammalian polysaccharides and some proteins. It is the hydrolysis product of chitin, the most important polysaccharide of crustacean and insect shells.

Galactosamine, as in glucosamine, is formed by attaching the amino group to the carbon atom number 2 of galactose. It is found in chondroitin sulfate, the characteristic polysaccharide of cartilage, and in many glycosphingolipids.

Neuraminic acids are D-sugars. It is formed by the combination of pyruvic acid and mannosamine. It is an important building block of animal cell walls. It is commonly found in bacteria and animal tissues as the structure of lipids, polysaccharides, glycoproteins and mucoproteins.

N-acyl derivatives of neuraminic acid are known as sialic acids. Sialic acids are found in the structure of glycoproteins in salivary gland secretion and other mucous secretions. It is also the building block of blood group substances.

Mumaric acid is an important building block of bacterial cell walls. Here, too, amino groups are acetylated to form N-acidyl mumaric acid.


The hemiacetal and hemiketal bond formed between the aldehyde group or ketone group in a monosaccharide and an alcoholic hydroxyl group in the molecule is also a glycosidic bond. If the glycosidic bond is formed in the monosaccharides D-glucose and D-fructose, the aD and bD forms of both sugars are formed.

This glycosidic bond can occur within the monosaccharide itself or between two monosaccharides. In this case, disaccharides are formed. If a glycosidic bond is formed between many monosaccharides, then polysaccharides are formed.

If methyl alcohol and glucose react, a glycosidic bond is formed between these two structures and a methyl glycoside is formed. Esters formed in this way are also called glycosides. They also have a- and b- shapes

There are many glycosides in nature that contain non-carbohydrate residues that yield sugars and alcohols when hydrolyzed. The carbohydrate portion of these glycosides is called glycone, and the non-carbohydrate portion is called aglycone. Due to the hydrophilic character of glycone, the glycoside is more soluble in water than the aglycone. Aglycones are phenolic compounds found mainly in plants, including various flavones and anthocyanins in flower-colouring substances. They are the polyphenol in phlorizin, a poisonous glycoside in the roots of many fruit trees, and the indoxyl aglycone found in the glycoside from which the indigo dye is obtained. The most important of the glycosides used in medicine is digitalis, known as cardiac glycoside.

3 – Disaccharides

Monosaccharides that combine to form disaccharides can be linked in two ways. The carbonyl group of one monosaccharide can be linked with the alcohol group of another monosaccharide. This type of bond is called maltose type bond. Maltose and lactose have this type of bond. Alternatively, the carbonyl group of one monosaccharide can be linked with the carbonyl group of another monosaccharide. This type of bond is also called trehalose type bond. Trehalose and sucrose have this type of bond. Since one of the active sugar groups is free in disaccharides with maltose type bonds, they show reducing properties.

The glycosidic bonds that provide the formation of disaccharides are of two types, alpha and beta. The position of the –OH group in C-1 determines the type of glycosidic bond.

Maltose was formed from two glucose residues. Carbon atom 1 of one of these two glucoses is connected with carbon number 4 of the other glucose residue, which has an unsubstituted anomeric carbon atom in its semi-acetal bond, by glycosidic bond. Therefore, maltose is a reducing sugar, reacts with carbonyl reagents, mutarotates. The configuration of the glycosidic bond in maltose is shown as a-1,4. This indicates that the non-reducing anomeric carbon (C-1) is in alpha-configuration and has formed a glycosidic bond with the hydroxyl group of carbon 3 atom of the other sugar. This type of binding is often denoted as alpha (1-4) using an arrow. The derived name for maltose, 4-0-aD-glucopyranosyl-D-glucopyranose, can be abbreviated as D-Glc-alpha (1-4)-D-Glc.

Lactose is synthesized only by secretory cells of the mammary glands during lactation. The amount of lactose in milk varies according to the type of mammal and is between 2 and 6%. It contains equal numbers of glucose and galactose molecules. Its structure is 4-0-Beta-D-galactopyranosyl-D-glucopyranose and abbreviated as D-Gal-b (1-4)-D-Glc.

Lactose is digested by enzymatic hydrolysis by intestinal mucosal cells. Lactase enzyme is very active in infants. However, except for northern Europeans and some Africans, lactase activity in the intestine is not common in adulthood. Intestinal lactase activity is very low in Far Easterners, Arabs, Jews, most Africans, Indians and people of Mediterranean race. Many people in this group are lactose intolerant. In these people who are lactose intolerant, lactose remains in the intestines without being absorbed. Large amounts of lactate taken with milk cause watery diarrhea and abdominal pain. This condition is called lactose intolerance. This condition is different from galactosemia, which is a genetic disease.

Sucrose is a well-known commercial and culinary sugar. Although it is found in different amounts in various plants, it is obtained from sugar cane or sugar beet for commercial purposes. Unlike many other disaccharides, sucrose's glycosidic bond is formed between the anomeric carbon atoms of its constituent monosaccharides, glucose and fructose. As a result, it is a non-reducing sugar. It neither shows mutarotation nor other properties based on the presence of semi-acetal or semi-ketal. The derived name of sucrose is aD-glucopyranosyl-bD-fructofuranoside. Its abbreviation is D-glc-(a 1 à 2)-D-fru.

  • Sugar cane
  • Sugar beet
  • Hydrolysis of Sucrose

Hydrolysis is the breakdown of a molecule into sub-molecules that take up water and form itself. Hydrolysis is carried out chemically (boiling with acid), or enzymatically (such as baker's yeast, wine yeast or brewer's yeast).< Acid Hydrolysis of Sucrose Approximately 5 ml. sucrose solution, 2.5 ml. water and 0.5 ml. It is mixed with concentrated HCl and heated in a water bath for 10 minutes, then cooled and neutralized with NaOH, it is seen that the Fehling test is positive. Since sucrose is broken down into glucose and fructose molecules (Hydrolysis) during heating with acid, it gains reducing properties. Sucrose + H2O -> Glucose + Fructose

Hydrolysis of Sucrose by Yeast

Sucrose can be hydrolyzed by acid as well as by yeast. a few ml. 1 ml on sucrose solution. The baker's yeast solution is added and heated for a while at 37 degrees Celsius (in a water bath). In the meantime, with the effect of the enzyme, sucrose is broken down into glucose and fructose and the reduction tests (Fehling) are positive.

4 – Polysaccharides

They are composed of many monosaccharide units. If they are hydrolyzed, they break down into their constituent monosaccharides. If the polysaccharide is the polymer of the same monosaccharide, it is called homopolysaccharide. Some polysaccharides contain other groups. These are also called heteropolysaccharides.

In the systematic naming of polysaccharides, the suffix "ose" at the end of the name of the monosaccharide that is included in the structure is removed and the suffix "an" is put. For example, if "glycose" generally denotes a monosaccharide, then the glycan thus derived from it is synonymous with a polysaccharide. A polysaccharide formed from a D-mannose or L-mannose is called mannan. If a glycan contains a type of monosaccharide as a building block, it is called homoglycan (homopolysaccharide). If it contains two or more types of monosaccharides, it is called Heteroglycan (Heteropolysaccharide).

Glycogen, amylopectin, amylose, cellulose and dextran are homopolysaccharides (homoglycans) containing D-glucose as monomer units. Pectin, D-galacturonic acid, inulin, D-fructose; chitin are homopolysaccharides (homoglycans) containing DN-acetyl-glucosamine. Many polysaccharides differ from each other not only by the monosaccharides they contain, but also by their molecular weights and other structural properties. Indeed, some polysaccharides are in straight chain form, while others are highly branched polymers. In all cases, the bonds connecting the monosaccharide units are always glycosidic bonds. These bonds can be alpha or beta, and successive units line up in a straight line or are linked by 1.2, 1.3, 1.4, or 1.6 bonds between units at branch points in the polymer.



Cellulose is the most abundant organic compound in the world. 50% or more of all carbon in plants is in the form of cellulose. That is, cellulose is usually a vegetable polysaccharide. Cotton is the purest source of cellulose and contains 90% cellulose. Cellulose gives glucose when fully hydrolyzed, and gives cellobiose, a disaccharide, when partially hydrolyzed. In cellulose, many glucose molecules are linked by a b-1,4 glycosidic bond.

Cellulose cannot be digested because there is no enzyme digesting this bond in the digestive system of monogastric organisms. Cellulase can be digested by the enzyme cellulase found in the rumen of equids and the caecum of equids.

Starch acts as a nutritional substitute for nutrition in plants. While glucose molecules are linked to each other by b-1,4 bonds in cellulose, they are linked to each other by a-1,4 bonds in starch. Therefore, the disaccharide unit repeated in the formation of starch is maltose, not cellobiose.

Starches are mixtures of two types of compounds that can be separated from each other. The part that has a long unbranched chain and resembles cellulose in this respect is called amylose. The amylose portion of starch is in the form of long chains that tend to spiral. Amylopectin is a branched chain polysaccharide. The average length of the branches varies with the species and the average length contains 24-30 glucose residues. The glycosidic bond of the main chain is α-1,4, but there are α-1,6 bonds at the branching points.

Starch is insoluble in cold water. With iodine solution, amylose gives a dark blue color and amylopectin gives a blue violet color. Starch gives complex color with iodine. Starch is hydrolyzed either by aqueous mineral acids or by special enzymes. The hydrolysis products of starch and the colors each of them give with iodine are as follows: In reaction with iodine, starch gives a blue color, amylodextrin gives a violet color, and erythrodextrin gives a red color. Does not color with acrodextrin.

Starch molecules are broken down into D-glucose molecules by undergoing a complete hydrolysis by three main types of enzymes. The first of these is the enzyme called alpha-amylase. Alpha-amylase enzyme is found in saliva and pancreatic secretion of animals. This enzyme randomly breaks straight amylose chains by acting on alpha 1à4 bonds. A mixture of glucose and maltose occurs in the environment. Beta-amylase in plants causes the formation of maltose units by acting on the non-reducing chain end bonds of amylase. Alpha and beta-amylases affect amylopectin. But they can unravel straight chains to their branching points. However, the 1α6 bonds close to the 1α4 bonds and the 1α6 glycoside bonds can be dissolved by a special enzyme. The name of this enzyme is "Branch Degrading Enzyme" or "alpha 1-6 glycosidase". Starch is broken down into maltose and eventually glucose units by the action of enzymes.

Hydrolysis of Starch

Polysaccharides adsorb iodine differently depending on the size of their molecules and give a colored complex. The complex is destroyed by heat and reshaped during cooling.

The blue color of starch with iodine is used for its recognition. Again, starch is hydrolyzed with a mineral acid (HCl), and the hydrolysis stages are followed by the different colors it gives with iodine. After the stages (partial hydrolysis) of amylodextrin (violet), erythrodextrin (red) and acrodextrin (colorless, only the color of iodine dominates), it is understood that the hydrolysis is complete (full hydrolysis) with the positive result of the Fehling experiment.

Acid Hydrolysis of Starch

About 2 g of starch is put in a test tube, 10-15 ml on it. cold distilled water is added and a suspension is formed by mixing well. 100 ml of this suspension boiling in a beaker. It is added to the water with continuous mixing. The following applications are made with this starch suspension.

a) About 1 ml of starch suspension into a test tube. The tube is taken under the tap and cooled with water, 1 drop of iodine or diluted lugol solution is added to it (avoid too much diluted iodine solution. Otherwise, its brown color masks the color of the complex). The resulting blue solution is heated until boiling and cooled again. Here, the color is lost due to the destruction of the starch-iodine complex with the effect of heat.

b) About 2 ml of starch suspension. is taken, about 2 ml on it. A mixture of Fehling A and Fehling B is added and heated.

c) 5 ml of starch suspension into a test tube. put 2 ml on it. 5% NaOH is added. It is heated until it boils and after that the heating is continued for another 2 minutes. Then it is cooled and neutralized by adding 1 drop of concentrated HCl, and the Fehling test is performed with this mixture.

d) 5 ml on the starch suspension remaining in the beaker. 15 ml of it after adding concentrated HCl. take the part of it into a test tube and dip it in boiling water in a beaker and leave it there for 15-20 minutes. In this way, starch is hydrolyzed by taking water. If a small sample is taken at the initial stage of hydrolysis and iodine solution or lugol solution is added, it gives a bluish red color. This indicates that amylodextrin is formed. After a while, if a small sample is taken again and checked with iodine solution or lugol solution, it gives a red color. This shows the formation of erythrodextrin. If, after a while, a small sample is taken and treated with iodine solution or lugol solution, the color will not form. This shows the formation of acrodextrin. After that, if heating is continued for a while and then Fehling tests are applied, it is seen that the test is positive, which shows the hydrolysis of starch to maltose and finally to glucose.

Hydrolysis of Starch by Saliva (Amylase)

a) 5 ml into a test tube. starch suspension is taken. By adding 1 drop of iodine solution or diluted lugol on it, the formation of blue color is ensured. Then, this mixture is added to the saliva collected in a second tube, mixed, and left to itself in a 37-degree water bath. It is observed that the color lightens rapidly.

With the effect of amylase in the saliva, the starch molecule begins to break down, causing the bond with iodine to dissolve and the color to become lighter. In further hydrolysis, the blue color disappears completely.

b) About 2 ml. saliva 8 ml. until mixed with water. This mixture is divided equally into 4 numbered tubes. 2 ml in each of the tubes. up to 0.5% starch suspension is added and immediately after shaking the first tube is boiled. Then, the tubes are left in a water bath at 37 degrees Celsius, and the formation of dextrins, which are the products of partial hydrolysis, is observed by applying the iodine test by taking samples from the 2nd tube after about 2 minutes, the 5rd tube after 3 minutes, and the 10th tube after 4 minutes. At the end of this period, it is checked whether the hydrolysis is completed by applying the Fehling test to each of the tubes.

It should be kept in mind that the duration of the experiment may vary due to individual differences in salivary amylase activity and the inability to regulate the temperature well, so it would be better for everyone to consider and record their own findings.

Glycogen is the animal equivalent of starch. Also called animal starch. It is found in significant amounts in the liver and muscle. Upon hydrolysis, it yields glucose units. Glycogen is a branched chain polysaccharide. It is more similar to amylopectin than amylose. It carries both α-1,4 and α-1,6 glycosidic bonds. There are 8-12 glucose residues for each non-reducing end group in glycogen. Its molecular weight ranges from 270.000 to 100 million.

Glycogen is present in the animal cell as particles much smaller than starch granules. Glycogen mixes easily with water and forms opalescent solutions. These solutions impart a violet-red color with iodine. Glycogen is relatively stable in hot alcohol, it can be precipitated from its aqueous solution by adding ethyl alcohol.

Dextrins are formed by the hydrolysis of starch with enzymes or acids. It consists of glucose units. It dissolves in water. It is used for feeding children.

Dextran is also a homopolysaccharide. It is produced by some microorganisms. Its building blocks are glucose. D-glucose molecules are joined by α-1,4-glycosidic bonds and have a straight chain structure. However, in some types of dextrans, branches are added with α-1,4 or α-1,3 bonds. Dextrans, which is formed by bacteria that reproduce on the surface of the teeth, is important as a component of dental plaques.

Dextran solution is often given to the patient to increase the volume of blood after blood loss. Because their viscosity is high, their osmotic pressure is low, their disintegration and use is slow, and their residence time in the blood circulation is long. In addition, dextran gel is widely used in column chromatography technique.

Agar-Agar is produced by seaweeds. It is a homopolysaccharide composed of D- and L-Galactose units. The units are linked by 1-3 glycosidic bonds. It also contains some sulfate in its structure. It is used in the preparation of culture media in bacteriology. Inulin is found in plants. It is a polymer of fructose. Fructose units are linked by b-2,1 glycosidic bonds. Since this polymer cannot enter the cell, it is used to measure the extracellular fluid volume. In addition, inulin is used to measure the filtration rate from the glomerulus.

Pectins are D-Galacttronic acid polymer. The units are linked by α-1,4 glycosidic bonds.

Sephadex is the trade name for a polysaccharide derivative. It is widely used in biochemical separation processes.


Not only simple sugars, but also some derivative compounds such as amino sugars and uronic acids are the building blocks of some polysaccharides. Most of these polysaccharides are the skeletal substance of the connective tissue or the mucous substance of the body. These are also called mucopolysaccharides or glycosaminoglycan.

Glykosaminoglycans have common structural principles. Glykosaminoglycans are made up of disaccharide units. The uronic acid found in these disaccharides is glycosidic bonded to carbon 3 of an acetylated amino sugar. These disaccharide units are attached to a flat macromolecule at the 1α4 site. In addition, the sulfuric acid may be ester-linked. The substance is strong acid due to uronic acids and sulfuric acid residues. Alongside the common D-glucuronic acid is L-Iduronic acid.

Hyaluronic Acid is the simplest member of this series, it is composed of glucuronic acid and N-Acetyl-glucosamine. The hyaluronic acid molecule is probably unbranched. It is an important component of the intercellular substance of acid-binding tissue. It is often found with protein in the fluid of Synovia, the vitreous of the eye, and the skin. It is obtained mainly from the umbilical cord. The rapid breakdown of hyaluronic acid by the enzyme called hyaluronidase is physiologically important. Hyaluronidase acts as a spreading factor in connective tissue and skin.

Chondroitin sulfate together with hyaluronic acid participate in the establishment of connective tissue. Especially cartilage chondroitin is rich in sulfuric acids. There are three different types defined in this group as chondroitin sulfate A, B and C. Chondroitin sulfate C (Chondroitin-6-sulfate) is built from glucuronic acid and N-acetyl-galactosamine-6-sulfate. In type A, sulfuric acid is located at carbon 4. So it is glucuronic acid and N-acetylgalactosamine-4-sulfate. In chondroitin sulfate B, the sulfate is in the 4th position as in chondroitin sulfate A. However, instead of glucuronic acid, its stereoisomer L-iduronic acid is present. Iduronic acid is the 5-epimer of glucuronic acid.

The structure of Keratan sulfate is N-acetyl-glucosamine, galactose and sulfate. It is the most important element of cartilage. It has been found in the cornea layer and aorta of the eye.

Dermatan sulfate is a polymer of iduric acid and N-acetyl-galactosamine-4-sulphate. It is found in the skin.

Heparin is a polysaccharide formed from the ester of sulfonylaminoglucose (glucosamine-N-sulfuric acid) and glucuronic acid. The attachment style is always a-1 à 4. Accordingly, heparin has a different organization from chondroitin sulfate. The amount of sulfuric acid it contains is very high. There are 4-5 molecules of sulfuric acid per unit of tatrasaccharide. The location of the sulfate residues may vary. Heparin has an anticoagulant effect; It prevents blood clotting by inhibiting the action of thrombin on fibrinogen and preventing the conversion of prothrombin to thrombin.

Cell Wall Structures of Bacteria These are complex structures with very large molecules called “Mureins”. N-acetyl-glucosamine and N-acetyl muramic acid are linked by b-(1 à 4) bond. Muramin acid is the 3-0-ether of lactic acid and glucosamine. The disaccharide units are again attached to a polysaccharide by b-1 to 4-glycosidic bonds.

Muramine acid glycoside is specifically degraded by Lysozym (= Muramidase), which is common in the animal kingdom.

Another group of cell wall components are Teichon acids. They are built from a polyalcohol (glycerin or ribitol) and phosphoric acid; Large chain complexes are formed via the phosphoric acid diester bond. N-Acetyl-glucosamine residues (glycosidic) and D-alanine (via ester bond) are placed on the free hydroxyl groups.

Blood Group Substances are found in the erythrocyte walls. D-glucosamine or D-galactosamine sometimes both contain some monosaccharides (D-galactose, L-fucose) and sialic acid. – Compiled from Lecture Notes

📩 08/07/2021 12:50

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