Carbohydrates

CARBOHYDRATESPrakash Pokhrel

CARBOHYDRATES • Most abundant organic compounds in the plant word

• Act as storehouses of chemical energy

• Components of supportive structures in plants

• Crustacean shells• Connective tissues in animals• Essential components of nucleic acids

CARBOHYDRATES • means “hydrate of carbon”• derives from the formula Cn(H2O)m

• Glucose: C6H12O6 or C6(H2O)6

• most are polyhydroxyaldehydes, polyhydroxyketones, or compounds that yield them after hydrolysis• saccharides – simpler members of the CHO family (Latin: saccharum – sugar)

• Monosaccharide, Disaccharide, Oligosaccharide, and Polysaccharide

A. MONOSACCHARIDES• C6H12O6

• with one of the carbons being the carbonyl group of either an aldehyde or a ketone

• have 3 to 9 carbon atoms

• -ose indicates that a molecule is a carbohydrate • tri-, tetr-, pent-, so and so forth - indicate the number of carbon atoms in the chain

A. MONOSACCHARIDES

•Aldoses

• monosaccharides containing an aldehyde group

A. MONOSACCHARIDES

•Ketoses

• monosaccharides containing a ketone group

A. MONOSACCHARIDES

•2 Trioses

• aldotriose glyceraldehyde

• ketotriose dihydroxyacetone

A. MONOSACCHARIDES• Fischer Projection Formulas• Glyceraldehyde – contains a stereocenter and therefore exists as a pair of enantiomers

• Enantiomer - is one of two stereoisomers that are non-superposable complete mirror images of each other, much as one's left and right hands are "the same" but opposite

A. MONOSACCHARIDES• D- and L- Monosaccharides•D-Monosaccharide

• has the –OH group on its penultimate carbon to the right

•L-Monosaccharide

• has the –OH group on its penultimate carbon to the left

A. MONOSACCHARIDES•D-

• specifies the configuration at the stereocenter farthest from the carbonyl group

•Prefixes (rib-, arabin-, and gluc-)

• specify the configuration of all other stereocenters in the monosaccharide relative to one another

•-ose• indicates that the compound is a carbohydrate

A. MONOSACCHARIDES•Most Abundant Hexoses

•D-Glucose•D-Galactose

• D-aldohexoses

•D-Fructose• D-ketohexose

A. MONOSACCHARIDES•Amino Sugars

• a monosaccharide in which an –OH group is replaced by an –NH2 group•D-Glucosamine•D-Mannosamine•D-Galactosamine

A. MONOSACCHARIDES•Physical Properties

• are colorless, crystalline solids

•Are very soluble in water• because hydrogen bonding is possible between their polar –OH groups and water

•Slightly soluble in ethanol•Insoluble in nonpolar solvents such as diethyl ether, dicloromethane, and benzene

A. MONOSACCHARIDES•Cyclic Structure

• Haworth Projection•A way to view furanose and pyranose forms of monosaccharides•The ring is drawn flat and viewed through its edge with the anomeric carbon (new C stereocenter created in forming the cyclic structure) on the right and the oxygen atom to the rear

•A 5- or 6-membered cyclic hemiacetal is represented as a planar pentagon or hexagon, respectively, lying roughly perpendicular to the plane of the paper


• Haworth Projection

•β means that the –OH on the anomeric carbon lies on the same side of the ring as the terminal –CH2OH

•α means that the –OH on the anomeric carbon lies on the side of the ring opposite from the terminal –CH2OH


• Haworth Projection

•-pyran- a 6-membered hemiacetal ring

•-furan- a 5-membered hemiacetal ring

•Pryanose and Furanose•Are used because monosacharide 5- and 6-membered rings correspond to the heterocyclic compunds pyran and furan

REACTIONS OFCARBOHYDRATE

REACTION OF MONOSACCHARIDES•Formation of Glycosides (Acetals)

•Acetal – yields when hemiacetal is treated with one molecule of alcohol

•Glycoside•A carbohydrate in which the –OH group on its anomeric carbon is replaced by an –OR group

•Glycosidic Bond•the bond from the anomeric carbon of a glycoside to an –OR group

Glycosides The hydroxyl group of anomeric carbon of a

carbohydrate can join with a hydroxyl group of another carbohydrate or some other compound to form a glycoside and the bond so formed is known as glycosidic bond.

eg. R-OH + HO-R’ R-O-R' + H2O The non-carbohydrate moiety is known as

aglycone –phenol, sterol, glycerol and methanol.

Glycosidic bond can be N-linked or, O- linked.

Streptomycin◦Antibiotic◦Given in Tuberculosis

Cardiac Glycosides –Digoxin, Digitoxin◦Used in cardiac insufficiency.◦Stimulate cardiac muscle contraction.◦Contain steroids as aglycone

component.

Ouabain –Sodium pump inhibitor.

Formation of Esters

Esterification of alcoholic groups of monosaccharides with phosphoric acid is a common reaction in metabolism.

Examples :Glucose-6-phosphate, andGlucose-1-phosphate.

ATP donates the phosphate moiety.

Glucose oxidase test

Glucose + O2

Glucose Oxidase

Gluconolactone + H2O2 H2O2 + (reduced colourless

dye)

Peroxidase

(Oxidized colored

dye)

Osazone Formation

All reducing sugars will form osazones with excess of phenyl hydrazine when kept at boiling temperature.

Glucose, Galactose and Fructose will produce the same needle-shaped crystals.

Molisch’s test

All carbohydrates when treated with conc. sulphuric acid undergo dehydration to give fufural compounds. These compounds condense with Alpha-napthol to form colored compounds.

Molish test is given by sugars with at least five carbons because it involves furfural derivatives, which are five carbon compounds.

Purple ring at junction

Fehling’s test

Same principle as benedicts testFehling’s A contains 7% copper

sulphate and Fehling’s B contains sodium potassium tartarate.

Oxidation

The glucuronic acid is used by the body for conjugation with insoluble molecules to make them soluble in water for detoxification purpose and also for synthesis of heteropolysaccharides.

Reduction to Form AlcoholsWhen treated with reducing agents

hydrogen can reduce sugars. Aldose yields corresponding alcohol.

Glucose is reduced to sorbitolmannose to mannitolfructose becomes sorbitol and mannitolGalactose is reduced to dulcitol andribose to ribitol.

Significance of reduction

Sorbitol, mannitol and dulcitol are used to identify bacterial colonies.

Mannitol is also used to reduce intracranial tension by forced diuresis.

The osmotic effect of sorbitol produces changes in tissues when they accumulate in abnormal amounts, e.g. cataract of lens.

Cataract Retinopathy Nephropathy Neuropathy

In maltose and lactose, there is still One carbonyl group attaching the 1st carbon Not engaged in the formation of glycosidic bond.It is reductable.So, they are still reducing sugars.In sucrose, both reductable carbonyl groups Are involved in the formation of glycosidic bond.So, it is a non-reducing sugarThe decomposition of disaccharides into

monosaccharides is called hydrolysis, Because one molecule of water should be added.

B. DISACCHARIDES and OLIGOSACCHARIDES•Disaccharides

• Sucrose (table sugar)

• most abundant• obtained principally from the juice of sugar cane and sugar beets• nonreducing sugar


• Lactose• principal sugar present in milk• consists of D-galactopyranose bonded by a beta-1,4-glycosidic bond to carbon 4 of D-glucopyranose• reducing sugar


• Maltose• derives its name from its presence in malt, the juice from sprouted barley and other cereal grains• consists of 2 units of D-glucopyranose joined by a glycosidic acid between carbon 1 of one unit and carbon 4 of the other unit

SucroseWhen sucrose is hydrolyzed, the products

have reducing action.

A sugar solution which is originally non-reducing, but becomes reducing after hydrolysis, is inferred as sucrose (specific sucrose test).Benedict's test is positive for

glucose. Test is negative for sucrose; but when sucrose is hydrolyzed, the test becomes positive (specific sucrose test)

B. DISACCHARIDES and OLIGOSACCHARIDES•Relative Sweetness

•Fructose• sweetest – even sweeter than sucrose

• Honey• D-fructose and D-glucose

•Lactose•almost no sweetness and is sometimes added to food as a filler

C. POLYSACCHARIDES•Polysaccharides

•Starch: Amylose and Amylopectin• used for energy storage in plants• complete hydrolysis yields only D-Glucose• Amylose – composed of continuous, unbranched chains of as many as 4000 D-glucose units joined by alpha-1,4-glycosidic bonds• Amylopectin – contains chains of as many as 10,000 D-glucose units joined by alpha-1,4-glycosidic bonds

• new chains of 24-30 units are started by alpha-1,6-glycosidic bonds

•Cellulose• most widely distributed plant skeletal polysaccharide• is a linear polysaccharide of D-glucose units joined by beta-1,4-glycosidic bonds

Physical property of polysaccharides

(1) Polysaccharides are insoluble in water and cannot give any taste.(2) As it cannot be dissolved in water, polysaccharides cannot move across the plasma membrane of the cell and cannot change the water potential of the water body. (3) No optical activity can be observed

Homopolysaccharides

StarchGlycoge

nCellulos

eInulinDextransChitin

Starch

It is the reserve carbohydrate of plantkingdom

Sources: Potatoes, cereals (rice,wheat) and other food grains.

Starch is composed of amylose andamylopectin.

Amylose

Amylopectin

OH

0

OH

OH

0 0

OH

0

OH

OH

n OH

0

n OH

Amylose is made up of glucose units with alpha-1,4 glycosidic linkages to form an unbranched long chain. Water soluble.

The insoluble part absorbs water and forms paste like gel; this is called amylopectin.

Amylopectin is also made up of glucose units, but is highly branched. The branching points are made by alpha-1,6 linkage

Iodine test for starch

Starch will form a blue colored complex with iodine; this color disappears on heating and reappears when cooled. This is a sensitive test for starch.

Starch is nonreducing because the free sugar groups are negligible in number.

Glycogen

It is the reserve carbohydrate in animals.It is stored in liver and muscle.

Liver glycogen stores increase during the well-fed state , and are depleted during a fast.

Glycogen is composed of glucose units joined by alpha-1,4 links in straight chains. It also has alpha-1,6 glycosidic linkages at the branching points.

Glycogen is more branched and more compact than amylopectin.

Liver and muscle glycogen

Cellulose

It is made up of glucose units combined with beta-1,4 linkages.

It has a straight line structure, with nobranching points.

Beta-1,4 bridges are hydrolyzed by the enzyme cellobiase. But this enzyme is absent in animal and human digestive system, and hence cellulose cannot be digested.

Importance

Fiber can absorb 10–15 times its own weight in water, drawing fluid into

the lumen of the intestine

Increasing bowel motility

1.Decrease the risk for constipation

It is a major constituent of fiber, thenondigestable carbohydrate.

Intestine

Bile salt Fibers

Excreted

Cholesterol

Decreases serum cholesterol level

.

2. Lower LDL cholesterol levels

Delays gastric emptying and can result in a sensation of fullness

4. Reduced peaks of blood glucose following a meal

Can bind various toxic substances including carcinogens & eliminate them in faecal matter

3.Decreases chances of some cancers

Inulin

It is a long chain homoglycan composed of D-fructose units with repeating beta-1,2 linkages.

It is the reserve carbohydrate present in various bulbs and tubers, such as onion, garlic.

It is clinically used to find renal clearance value and glomerular filtration rate.

Dextrans

These are highly branched homopolymers of glucose units with 1-6, 1-4 and 1-3 linkages. They are produced by micro- organisms.

Since they will not easily go out of vascular compartment, they are used for intravenous infusion as plasma volume expander for treatment of hypovolemic shock.

D-glucose is otherwise called Dextrose, a term often used in bed-side medicine, e.g. dextrose drip.

Dextrin is the partially digested product of starch.

Dextran is high molecular weightcarbohydrate, synthesized by bacteria.

It is present in exoskeletons of insect. It is composed of units of N- acetylglucosamine with beta-1,4 glycosidic linkages.

Heteropolysaccharides

• . Agar• Mucopolysaccharide

Agar

Agar = The linear polysaccharide Agarose+ agaropectin

It is dissolved in water at 100ºC, which upon cooling sets into a gel. Agarose is used as matrix for electrophoresis.

Agar cannot be digested by bacteria and hence used widely as a supporting agent to culture bacterial colonies.

Mucopolysaccharideglycosaminoglycans(GAGs)[acidic sugar–amino sugar]n.

Because of their large number of negative charges, these heteropolysaccharide chains tend to be extended in solution. They repel each other, and are surrounded by a shell of water molecules. When brought together, they “slip” past each other.

This produces the “slippery” consistencyof mucous secretions and synovial fluid.

ImportanceAmino sugars Found in

Glucosamine Hyaluronic acid, heparin andblood group substances

Galactosamine Chondroitin sulphate of cartilage, bone and tendons.

Mannosamine constituent of glycoproteins

N-acetylglucosamine (GluNac) and N- acetyl galactosamine (GalNac)

constituents of glycoproteins, Mucopolysaccharide and cell membrane antigens.

GAGs Composition Tissue distribution Functions

Hyaluronic acid

D-glucuronic acid and N-acetyl D- glucosamine

Connective tissue Synovial fluid Vitreous humor Gel around ovum

lubricant and shock absorbant in joints

Chondroitin sulphate

D-glucuronic acid and N- acetyl D-galactosamine4-sulfate.

bone, cartilage, Tendons,heart valves and skin.

Helps to maintain the structure And shapes of tissues

Dermatansulfate

D-Iduronic acid andN-acetyl D-galactosamine4 –sulfate.

Skin Helps to maintainshapes of tissues

Keratan sulphate

galactose and N-acetyl glucosamine

cornea tendons

Keeps cornea Transparent

Heparin sulphated glucosamine and glucuronic acid or iduronic acid

blood, lung, liver,kidney, spleen

Anticoagulant Clearing factor

Hyaluronidase

Breaks b(1-4 linkages) in hyaluronic acid.

Present in high concentration in testes, seminal fluid, and in certain snake and insect venoms.Hyaluronidase of semen clears the gel (hyaluronic acid) around the ovum allowing a better penetration of sperm into the ovum.Serves important role in fertilization

Hyaluronidase of bacteria helps their invasioninto the animal tissues.

Heparin is an anticoagulant( preventsblood clotting).

Heparin helps in the release of the enzyme lipoprotein lipase which helps in clearing the turbidity of lipemic plasma.

Lipoprotein lipase breaks TG in glyceroland FFA.

Proteoglycans: When carbohydrate chains are attached to a polypeptide chain.

Glycoproteins: Carbohydrate content ≤10%.

Glycoprotein Major functionGlycophorin glycoprotein of

erythrocytes cell membrane

Collagen Structure of cartilage and bone

Ceruloplasmin Transport proteinImmunoglobulin Defense against

infectionIntrinsic factor Absorption of vitamin

B12Fibrinogen Blood clotting

Thank you

Carbohydrates

Education

Transcript of Carbohydrates