Carbohydrate 2nd lecture Biochemistry

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Carbohydrate Carbohydrate chemistrychemistry

StreaksStreaks

CarbohydratesCarbohydrates Carbohydrates are polyhydroxy Carbohydrates are polyhydroxy

aldehydes or ketons.aldehydes or ketons.

Classification of carbohydratesClassification of carbohydrates

Carbohydrates are classified into:Carbohydrates are classified into:– monosaccharides,monosaccharides,– disaccharides, disaccharides, – oligosaccharidesoligosaccharides– polysaccharides.polysaccharides.

SaccharidesSaccharidesScientist use the word saccharides to Scientist use the word saccharides to describe sugars describe sugars Greek “Greek “sakcharon”sakcharon” = = sugarsugar..If there is only one sugar molecule it is If there is only one sugar molecule it is known as a known as a monosaccharidemonosaccharideIf there are two it is a If there are two it is a disaccharidedisaccharideWhen there are a whole bunch, it is a When there are a whole bunch, it is a polysaccharidepolysaccharide..

MonosaccharidesMonosaccharides The simplest form of carbohydratesThe simplest form of carbohydrates

They are further classified according They are further classified according to:to:

The number of carbon atoms in The number of carbon atoms in its backboneits backbone

The functioning group (aldehyde The functioning group (aldehyde or ketone)or ketone)

No. of

carbonsName Aldehyde Ketone

3 Triose Glyceraldehyde Dihydroxy

acetone4 Tetrose Erythrose Erythrulose

5 Pentose Ribose Ribulose

6 Hexose Glucose-

Galactose-

Mannose

Fructose

7 Heptose Sedoheptulose 66

Most of the names of Most of the names of carbohydrates end in -carbohydrates end in -oseose

GlucGlucoseose-What plants make-What plants make MaltMaltoseose- used in making beer - used in making beer (disaccharide)(disaccharide)FructFructoseose – found in fruit – found in fruit (monosaccharide)(monosaccharide)SucrSucroseose- Table sugar (disaccharide)- Table sugar (disaccharide)LactLactose ose – In milk (disaccharide)– In milk (disaccharide)

Carbohydrates – polyhydroxyaldehydes or polyhydroxy-ketones of formula (CH2O)n, or compounds that can be hydrolyzed to them. (aka sugars or saccharides)Monosaccharides – carbohydrates that cannot be hydrolyzed to simpler carbohydrates; eg. Glucose or fructose.

Disaccharides – carbohydrates that can be hydrolyzed into two monosaccharide units; eg. Sucrose, which is hydrolyzed into glucose and fructose.

Oligosaccharides – carbohydrates that can be hydrolyzed into a few monosaccharide units.

Polysaccharides – carbohydrates that are are polymeric sugars; eg Starch or cellulose.

Aldose – polyhydroxyaldehyde, eg glucoseKetose – polyhydroxyketone, eg fructoseTriose, tetrose, pentose, hexose, etc. – carbohydrates that contain three, four, five, six, etc. carbons per molecule (usually five or six); eg. Aldohexose, ketopentose, etc.

Of these; trioses, pentoses and hexoses are most common in cells.

If the carbon chain is long enough (five or more carbons), the alcohol at one end of a monosaccharide can attack the carbonyl group (aldehyde or ketone) at the other end to form a cyclic compound (hemiacetal or hemiketal respectively).

When a When a six-memberedsix-membered ring is formed, the ring is formed, the product of this reaction is called a product of this reaction is called a pyranosepyranose

When a When a five-memberedfive-membered ring is formed, it is ring is formed, it is called a called a furanosefuranose

The rings can open and re-close, allowing rotation to occur around the carbonyl

carbon resulting in :– Two distinct configurations (α and β

anomers) of the hemiacetals and hemiketals are present.

The anomeric carbon is the carbonyl carbon (C1 of aldose or C2 of ketose).

Carbohydrates can change spontaneously between the α and β configurations-- a process known as mutarotation.

Pyranose ring

B. B. AAnomerismnomerismSugars in solution exist in ring form and not in straight chain Sugars in solution exist in ring form and not in straight chain

formform . .Aldosugar form mainly Aldosugar form mainly pyranosepyranose ring and ketosugar form ring and ketosugar form furanosefuranose ring structure ring structure

Carbon Carbon 11, after ring formation becomes asymmetric and it is , after ring formation becomes asymmetric and it is called as anomeric carbon atom. If the two sugars which differ called as anomeric carbon atom. If the two sugars which differ in the configuration at only in the configuration at only C1C1 in case of aldoses and in case of aldoses and C2C2 in in ketoses are known as anomers and represented as alpha and ketoses are known as anomers and represented as alpha and

beta sugarsbeta sugars . .E.g. E.g. -D glucose and -D glucose and -D-glucose-D-glucose

-D fructose and -D fructose and -D-fructose-D-fructose

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Furanose ring

D-fructose α - D-fructofuranose β -D-fructofuranose

ISOMERISM IN CARBOHYDRATESISOMERISM IN CARBOHYDRATES•The presence of asymmetric carbon atoms (A The presence of asymmetric carbon atoms (A

carbon atom to which four different atoms or carbon atom to which four different atoms or groups attached is known as asymmetric groups attached is known as asymmetric carbon) in a compound produces following carbon) in a compound produces following effecteffect;;

•Sterioisomerism of the compoundSterioisomerism of the compound •Confers optical activity to the compoundConfers optical activity to the compound..

11 . .SterioisomerismSterioisomerismCompounds which are identical in composition Compounds which are identical in composition and structural formula but differ in spatial and structural formula but differ in spatial configuration are called as sterioisomers. configuration are called as sterioisomers. These includeThese include

IsomersIsomers These are compounds that have These are compounds that have

the same chemical formula e.g. the same chemical formula e.g. – glucose,glucose,– fructose, fructose, – mannose and mannose and – galactose galactose – all have the chemical formula all have the chemical formula

CC66HH1212OO66..1717

EpimerismEpimerism:: The isomers formed due to variations in the The isomers formed due to variations in the configuration of configuration of –H–H and and –OH–OH around a single chiral around a single chiral carbon atom in a sugar molecule is called as carbon atom in a sugar molecule is called as

epimersepimers . .Mannose is 2 – epimer of glucose because these two Mannose is 2 – epimer of glucose because these two

have different configuration only around C2have different configuration only around C2 . .Galactose is 4-epimer of glucose [at C4]Galactose is 4-epimer of glucose [at C4]

2 .Optical activityThe compounds having asymmetric carbon atoms can rotate the beam of plane polarized light and are said to be optically active .

An isomer which can rotate the plane of polarized light to the right is called as

dextrorotatory and is designated as (d) or)+( Example: D- (d)-glucose or it is also known as dextrose .

While the isomer which rotates the plane of polarized light to left is known as

levorotatory, and is identified as (l) or.)-( Example: D-(l)-fructose.

Enantiomers Enantiomers (sterioisomers)(sterioisomers)

These are special type of isomers in which the structure is present in 2 pairs which are mirror images to each other, resulting in D and L forms

All carbohydrates contain at least one All carbohydrates contain at least one chiral chiral (asymmetrical) carbon(asymmetrical) carbon and are, therefore can exist and are, therefore can exist in either of two conformations, as determined by in either of two conformations, as determined by the the orientation of the hydroxyl group around the orientation of the hydroxyl group around the asymmetric carbon farthest from the carbonyl. asymmetric carbon farthest from the carbonyl.

The stereoisomer in which the -The stereoisomer in which the -OH extends to the OH extends to the right right is called is called D-glyceraldehydeD-glyceraldehyde (from the Latin (from the Latin dexter= right), and the stereoisomer in which the -dexter= right), and the stereoisomer in which the -OH extends to the left OH extends to the left is is L-glyceraldehydeL-glyceraldehyde (from (from laevus = left). laevus = left).

Enantiomers (sterioisomers) Enantiomers (sterioisomers) D - and L - isomersD - and L - isomers

With a few exceptions, those carbohydrates that are of physiological significance exist in the D-conformation

Reactions involving Reactions involving monosaccharidemonosaccharidess

Reducing sugars: The sugar is reducing if the

oxygen of the anomeric carbon (carbonyl oxygen) is not attached to any other structure.

So glucose, galactose and fructose are reducing sugars while sucrose is not.

Reducing sugars react with Benedict reagent.

Oxidation reduction reactionsOxidation reduction reactions

Oxidation of hydroxyl group at C6 to carboxyl group produces uronic a.

• glucose gives glucuronic acid,

• galactose gives galacturonic acid..

Reduction of aldehyde or keton group produces alcohol

– glucose gives sorbitol,

– galactose gives galactilol,

– ribose gives ribitol

Glycosidic bondsGlycosidic bonds It is the bond formed between It is the bond formed between OH OH group of group of

anomeric carbonanomeric carbon and a and a OHOH group or group or aminoamino group of other compound called group of other compound called aglycone aglycone

– If the group of aglycone is OH group, then If the group of aglycone is OH group, then it is O-glycoside bond (e.g. disaccharides).it is O-glycoside bond (e.g. disaccharides).

– If the group of aglycone is NH2 group, If the group of aglycone is NH2 group, then it is N-glycosidethen it is N-glycoside..

DisaccharidesDisaccharides

The two monosaccharides are linked by The two monosaccharides are linked by a glycosidic bond to form disaccharides a glycosidic bond to form disaccharides

Physiologically important disaccharides Physiologically important disaccharides are:are:– sucrosesucrose– lactoselactose– maltose. maltose.

Sucrose

•Found in sugar cane and sugar beets•It is composed of glucose and fructose linked by a-(1,2) -glycosidic bond

LactoseLactose

It It is found in the milk of mammalsis found in the milk of mammals It consists of It consists of galactosegalactose and and glucoseglucose in a b- in a b-

(1,4) glycosidic bond. (1,4) glycosidic bond.

MaltoseMaltose The major degradation product of starchThe major degradation product of starch It is composed of It is composed of 2 glucose 2 glucose monomers in monomers in

an an αα-(1,4) glycosidic bond. -(1,4) glycosidic bond.

PolysaccharidesPolysaccharides Most of the carbohydrates found in nature Most of the carbohydrates found in nature

occur in the form occur in the form polysaccharides. polysaccharides.

The main building blocks in The main building blocks in polysaccharides is polysaccharides is D-glucose.D-glucose.

When polysaccharides are composed of a When polysaccharides are composed of a single monosaccharide, they are termed single monosaccharide, they are termed homopolysaccharides.homopolysaccharides.

Polysaccharides composed of more than Polysaccharides composed of more than one type of monosaccharide are termed one type of monosaccharide are termed heteropolysaccharidesheteropolysaccharides. .

OligosaccharidesOligosaccharides Contain 3 - 10 molecules of Contain 3 - 10 molecules of

monosaccharide unitsmonosaccharide units.. eg: Maltotriose eg: Maltotriose

(glucose+glucose+glucose)(glucose+glucose+glucose)

PolysaccharidesPolysaccharides Contain more than 10 molecules of Contain more than 10 molecules of

monosaccharide unitsmonosaccharide units Classified into Classified into homopolysaccharideshomopolysaccharides

and and heteropolysaccharidesheteropolysaccharides3232

a) a) HomopolysaccharideHomopolysaccharide : : Polymer of same monosaccharide unitsPolymer of same monosaccharide units

ExamplesMonosaccharide Unit SourcesStarch Glucose Plant, rice

Dextrin Glucose from starch hydrolysisGlycogen Glucose liver, muscleCelluloseGlucose Plant fibers

Inulin Fructose dahlia rootsChitin N-acetyl glucosamine Shells of arthropod

Hydrolysis Hydrolysis Hydro=water lysis= break Hydro=water lysis= break

apartapartHydrolysis breaks down a Hydrolysis breaks down a disaccharide molecule disaccharide molecule into its original into its original monosaccharidesmonosaccharides..Hydrolysis, it means that Hydrolysis, it means that water splits a water splits a compoundcompound..When sucrose is added When sucrose is added to water, it splits apart to water, it splits apart into glucose and into glucose and fructosefructose..

Do Too many carbohydrates Do Too many carbohydrates make us fatmake us fat!!

If you eat more If you eat more calories than you calories than you expend in energy, expend in energy, then anything can then anything can be stored as fat - be stored as fat - protein, fat or protein, fat or carbohydratecarbohydrate . .

However if you do not take in However if you do not take in any carbohydrates into your any carbohydrates into your body you will use fat as fuelbody you will use fat as fuel..

Thank god for the low carb diet. Now, nobody wants to eat me because they

think I make them fat.

What do we do with all the What do we do with all the sugarsugar??

Plants store glucose Plants store glucose in the form of in the form of polysaccharides polysaccharides known as known as starchstarch in in

their rootstheir roots ..

Animals store Animals store glucose in the glucose in the from of a from of a polysaccharide polysaccharide known as known as glycogenglycogen in our in our liver and muscle liver and muscle cellscells..

CelluloseCellulose

The most abundant The most abundant organic molecule on organic molecule on earthearth..Gives trees and plants Gives trees and plants structure and strengthstructure and strength..Most animals can not Most animals can not break the glucose break the glucose linkage by normal linkage by normal means of hydrolysis. means of hydrolysis. Need special enzymesNeed special enzymes..We need cellulose (fiber) We need cellulose (fiber) to keep our digestive to keep our digestive tracts clean and tracts clean and

healthyhealthy . .

Polysaccharides are used in Polysaccharides are used in the shell of crustaceans like the shell of crustaceans like

crabs and lobsters.crabs and lobsters.ChitinChitin

ChitinChitin: A nitrogenous : A nitrogenous derivative of derivative of cellulose that is that is found in abundance in the found in abundance in the exoskeletons of insects and exoskeletons of insects and crustaceans, as well as the crustaceans, as well as the cell walls of many fungicell walls of many fungi..

Carbohydrates also serve as Carbohydrates also serve as structural elementsstructural elements..

The chains sticking out of the The chains sticking out of the proteins in the cell membrane are proteins in the cell membrane are polysaccharides know as cell polysaccharides know as cell markersmarkers..

StarchStarch Starch is the major storage form of Starch is the major storage form of

carbohydrate in plant cells.carbohydrate in plant cells.

Unbranched starch is called Unbranched starch is called amyloseamylose;; branched starch is called branched starch is called amylopectinamylopectin

Amylose - Is a glucose polymer with - Is a glucose polymer with a (1a (1--4)4) glycosidic glycosidic

bond. bond. - The end of the polysaccharide with an anomeric - The end of the polysaccharide with an anomeric

carbon (C1) that is not involved in a glycosidic carbon (C1) that is not involved in a glycosidic bond is called the bond is called the reducing endreducing end..

Amylopectin:- is a glucose polymer with mainly a(1-4) linkages, - but it also has branches formed by a(1-6) linkages. -The branches produce:

- a compact structure,-and provide multiple chain ends at which enzymatic cleavage of the polymer can occur.

GlycogenGlycogen:: - - Glycogen is the major form of stored Glycogen is the major form of stored

carbohydrate in animals.carbohydrate in animals. - It is a homopolymer of glucose linked - It is a homopolymer of glucose linked

by a-(1,4) glycosidic linkageby a-(1,4) glycosidic linkage

- it is also highly branched, with a-- it is also highly branched, with a-(1,6) branch linkages occurring every (1,6) branch linkages occurring every 8-10 residues8-10 residues..

CelluloseCellulose, a major constituent of plant cell walls, , a major constituent of plant cell walls, consists of long linear chains of glucose, with consists of long linear chains of glucose, with b (1b (1--

4) 4) linkageslinkages..

Lactose IntoleranceLactose Intolerancemore lactose is consumed than can be more lactose is consumed than can be digesteddigestedlactose molecules attract waterlactose molecules attract watercause floating, abdominal discomfort, diarrheacause floating, abdominal discomfort, diarrheaintestinal bacteria feed on undigested intestinal bacteria feed on undigested lactoselactoseproduce acid and gasproduce acid and gas

Glucose HomeostasisGlucose Homeostasismaintaining an even balance of maintaining an even balance of glucose is controlled by insulin and glucose is controlled by insulin and glucagonglucagoninsulininsulinmoves glucose into the bloodmoves glucose into the bloodglucagonglucagonbrings glucose out of storagebrings glucose out of storage

Maintaining Blood

Glucose Homeostasi

IntestineWhen a person eats,blood glucose rises.

Insulin stimulates the uptake of glucose into cells and storage

as glycogen in the liver andmuscles. Insulin also stimulates

the conversion of excessglucose into fat for storage.

7 Blood glucose begins torise.

a The stress hormoneepinephrine and other hormonesalso bring glucose out of storage.

GlucoseInsulin

GlucagonGlycogen

Glucagon stimulates livercells to break down glycogenand release glucose into the

blood.a

Low blood glucose stimulatesthe pancreas to release

glucagon into the bloodstream.

As the body's cells useglucose, blood levels decline.

Glucagon

Pancreas

Fat cell

Muscle

High blood glucose stimulatesthe pancreas to release insulin.

Pancreas

Insulin

ImbalanceImbalancediabetesdiabetesafter food intake, blood glucose rises and is after food intake, blood glucose rises and is not regulated because insulin is not regulated because insulin is inadequateinadequatehypoglycemiahypoglycemiablood glucose drops dramaticallyblood glucose drops dramaticallytoo much insulin, activity, inadequate food too much insulin, activity, inadequate food intake, illnessintake, illnessdiet adjustment includes fiber-rich carbs and diet adjustment includes fiber-rich carbs and proteinprotein

SugarSugar

½ ½comes from natural sources, ½ comes from natural sources, ½ from refined and addedfrom refined and addedsucrose, corn syrup, honeysucrose, corn syrup, honeyexcess can lead to nutrient excess can lead to nutrient deficiencies and tooth decaydeficiencies and tooth decayempty caloriesempty caloriessugar and starch break down in the sugar and starch break down in the mouthmouth

Starch and FiberStarch and Fiberdiet that includes starch, fiber and diet that includes starch, fiber and natural sugarsnatural sugarswhole grains, vegetables, legumes, fruitswhole grains, vegetables, legumes, fruitsmay protect against heart disease and strokemay protect against heart disease and strokereduces the risk of type 2 diabetesreduces the risk of type 2 diabetesenhances the health of the large intestineenhances the health of the large intestinecan promote weight losscan promote weight loss

Starch and FiberStarch and Fiberstarch intakestarch intake45-65%45-65%

225225 – – 325325 grams (DV is 300 grams (DV is 300 grams)grams)

900-1300900-1300 kcal/2000 kcalkcal/2000 kcalRDA is 130 gramsRDA is 130 gramsfiber intakefiber intakeDaily Value is 25 grams/2000 Daily Value is 25 grams/2000 kcalkcal

Artificial SweetenersArtificial Sweetenershelp keep sugar and energy intake downhelp keep sugar and energy intake downanything we eat has FDA approvalanything we eat has FDA approval

–saccharinsaccharin–aspartameaspartame

–acesulfame potassiumacesulfame potassium–sucralosesucralose–neotameneotame

Sugar ReplacersSugar Replacerssugar alcoholssugar alcoholsprovide bulk and sweetnessprovide bulk and sweetnesscookies, gum, candy, jellycookies, gum, candy, jellydo contain minimal kcaldo contain minimal kcallow glycemic responselow glycemic responseabsorbed slowlyabsorbed slowlydo not cause dental cariesdo not cause dental caries

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Carbohydrate 2nd lecture Biochemistry

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