Karaganda State Medical University. Chemistry department. Lecture on the topic: Carbohydrates. For the 1st year students of specialty “General medicine". Discipline: Chemistry. Lecturer: PhD, Associate Professor Vlassova Lenina. Karaganda 2014

The objectives of the lecture: 1. 1.You need to be able to distinguish and classify the carbohydrates You should know how to write the structural formulas of simple carbohydrates in various projections (Haworth projection and Fischer projection) You should know the chemical properties of carbohydrates according to their structure You should know the importance of carbohydrates to living organisms.

Plan of the lecture: 1. Definition and classification of carbohydrates. 2. Monosaccharides, their structure and properties. 3. Disaccharides, their structure and properties. 4. Polysaccharides, their structure and importance to the body.

Definition of carbohydrates. The Carbohydrates - are natural compounds having in the vast majority the composition of Cx (H2O) y. Cx (H2O) y. According to the ability to be hydrolyzed carbohydrates are divided into simple – the monosaccharides and complicated – the polysaccharides. Monosaccharides are not hydrolyzed with the formation of the simple carbohydrate.

CARBOHYDRATES Formerly the name "carbohydrate" was used in chemistry for any compound with the formula C m (H 2 O)n Monosaccharides Disaccharides Oligosaccharides and polysaccharides

Definition of polysaccharides. The polysaccharides are high molecular weight compounds whose macromolecules contain hundreds or thousands of monosaccharide units. Among them are a group of oligosaccharides having a relatively low molecular weight and containing from 2 to 10 monosaccharide units.

MONOSACCHARIDES Monosaccharides are the simplest carbohydrates in that they cannot be hydrolyzed to smaller carbohydrates. They are aldehydes or ketones with two or more hydroxyl groups. If the carbonyl group is an aldehyde, the monosaccharide is an aldose. If the carbonyl group is a ketone, the monosaccharide is a ketose.

Мonosaccharides. The Monosaccharides - are poly- hydroxycarbonyl compounds in which each carbon atom (except the carbonyl group) associated with an OH group. The general formula of monosaccharides - Cn (H2O) n, where n = 3-9. n = 3-9.

On chemical structure monosaccharides are distinguished: aldoses - the monosaccharides containing an aldehyde group; ketoses - the monosaccharides containing a ketone group (typically at the second carbon atom.) Depending on the length of the carbon chain monosaccharides are divided into: trioses, tetroses, pentoses, hexoses, etc.

Classification of. Classification of aldoses.

Сlassification of ketosis.

Hexoses (D-glucose, D-galactose, D-mannose, D-fructose) and pentoses (D-ribose, D-xylose, D- arabinose) is widely distributed in nature. Among the derivatives of monosaccharides are the most common amino sugars D-glucosamine and D- galactosamine and 2-deoxy-D-ribose.

The monosaccharides are in linear form (30%) and cyclic forms (70%) in a dissolved state. Anomeric isomerism is typical for cyclic forms of monosaccharides. Anomers - are isomers which differ in configuration of the anomeric carbon atom.

The formation of cyclic forms of monosaccharides. The formation of hemiacetal.

The structure of glucose – the pyranose and the furanose forms. α α Haworth projection formula are depicted by a six-membered pyranose ring (named from pyran) or a five- membered furanose ring (named from furan). The cyclic forms of glucose are known as α  -D- glucopyranose and α  -D-glucofuranose.

If the free hemiacetal hydroxyl group is under the furanose or pyranose ring it will be the ά-anomer. The β-anomer will have the free hemiacetal hydroxyl group is above of the furanose or pyranose ring. Cyclic forms of monosaccharides represented with using Haworth formulas.

For example, in a solution of the D-glucose predominates the β-D-glucopyranose:

Disaccharides. Disaccharides consist of two monosaccharide residues bound by a glycosidic linkage. Probably two variants of glycoside bond formation: 1/ at the expense of hemiacetal hydroxyl of the one monosaccharide and alcoholic hydroxyl another monosaccharide; 2/ through the hemiacetal hydroxyl of both monosaccharides.

Disaccharides are formed by condensation reaction. Hydrolysis reaction - is the reverse reaction and this results to the formation of sugars.

The reaction of formation of maltose

The most important of them are maltose, cellobiose, lactose and sucrose. Maltose is contained in the malt and is produced by incomplete hydrolysis of starch. Maltose molecule consists of two residues of α-D-glucopyranose units connected by α-1,4 - glycosidic bond.

Cellobiose - a product of incomplete hydrolysis of the cellulose fiber. Cellobiose molecule consists of two residues of β-D- glucopyranose linked β-1,4-glycosidic bond. Cellobiose - reducing disaccharide.

Lactose contained in milk (4-5%). The molecule of lactose consists of residues β-D- galactopyranose and α-D-glucopyranose linked β-1,4-glycosidic bond. Lactose - reducing disaccharide.

Sucrose is contained in sugar cane, sugar beet, plants and fruit juices. It is composed of residues of α-D-glucopyranose and β-D- fructofuranose which are connected through the a hemiacetal hydroxyl. Sucrose - nonreducing disaccharide.

Polysaccharides. Polysaccharides -are polymers constructed from monosaccharide residues linked by glycosidic bonds. The polysaccharides may be linear or branched structure. Polysaccharides consist of the same monosaccharide residues, called gomopolisaharides and of different monosaccharide residues - heteropolysaccharides.

STARCHSTARCH α –amylose α –amylopectin

α –amylose α –amylopectin

The chemical properties of starch similar to the properties mono-and disaccharides. The starch is hydrolyzed by the action of acids (but not bases) and the amylase enzyme. The end product of starch hydrolysis is D-glucose. (C6H10O5)n ---> (C6H10O5)m ---> C12H22O11 ---> C6H12O6 starch, maltose, dextrins D-glucose n> m

Glycogen. Glycogen is the carbohydrate reserve in animals, hence often referred to as animal starch. It is present in high concentration in liver, followed by muscle, brain etc. Glycogen is also found in plants that do not possess chlorophyll (e.g. yeast, fungi). The structure of glycogen is similar to that of amylopectin with more number of branches. Glucose is the repeating unit in glycogen joined together by  (1  4) glycosidic bonds, and  (1  6) glycosidic bonds at branching points (Fig.). The molecular weight (up to 1 x 10 8 ) and the number of glucose units (up to 25,000) vary in glycogen depending on the source from which glycogen is obtained.

Cellulose. Cellulose occurs exclusively in plants and it is the most abundant organic substance in plant kingdom. It is a predominant constituent of plant cell wall. Cellulose is totally absent in animal body. Cellulose is composed of β-D-glucose units linked by β (1  4) glycosidic bonds.

Hyaluronic acid, Hyaluronic acid is an important GAG found in the ground substance of synovial fluid of joints and vitreous humor of eyes. It is also present as a ground substance in connective tissues, and forms a gel around the ovum. Hyaluronic acid serves as a lubricant and shock absorbant in joints. Hyaluronic acid is composed of alternate units of D-glucuronic acid and N-acetyl D-glucosamine. These two molecules form disaccharide units held together by β (1  3) glycosidic bond. Hyaluronic acid contains about ,000 disaccharide units (held by β 1  4 bonds) with a molecular weight up to 4 million.

Chondroitin sulfates. Chondroitin 4-sulfate (Greek: chondros-cartilage) is a major constituent of various mammalian tissues (bone, cartilage, tendons, heart, valves, skin, cornea etc.). Structurally, it is comparable with hyaluronic acid. Chondroitin 4-sulfate consists of repeating disaccharide units composed of D-glucuronic acid and N-acetyl D-galactosamine 4-sulfate.

Thank you for your attention.