1 carbohydrates structure and biological function monosaccharides carbohydrates in cyclic structures...

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CarbohydratesStructure and Biological Function

CarbohydratesStructure and Biological Function

Monosaccharides

Carbohydrates in Cyclic Structures

Reactions of Glucose and Other Monosaccharides

Polysaccharides

Glycoproteins

Monosaccharides

Carbohydrates in Cyclic Structures

Reactions of Glucose and Other Monosaccharides

Polysaccharides

Glycoproteins

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CarbohydratesCarbohydrates

Compounds containing C, H and O

General formula : Cx(H2O)y

All have C=O and -OH functional groups.

Classified based on •Size of base carbon chain•Number of sugar units •Location of C=O•Stereochemistry

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Types of carbohydratesTypes of carbohydrates

Classifications based on number of sugar units in total chain.

MonosaccharidesMonosaccharides - single sugar unit

DisaccharidesDisaccharides - two sugar units

OligosaccharidesOligosaccharides - 2 to 10 sugar units

PolysaccharidesPolysaccharides - more than 10 units

Chaining relies on ‘bridging’ of oxygen atoms

glycoside bondsglycoside bonds

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StereoisomersStereoisomers

StereochemistryStereochemistryStudy of the spatial arrangement of molecules.

Stereoisomers haveStereoisomers have•the same order and types of bonds.•different spatial arrangements.

•different properties.

Many biologically important chemicals, like sugars, exist as stereoisomers. Your body can tell the difference.

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EnantiomersEnantiomers

Pairs of stereoisomersPairs of stereoisomers

Designated by D- or L- at the start of the name.

They are mirror images that can’t be overlapped.

If you don’t believe it,give it a try!

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L- and D- glyceraldehydeL- and D- glyceraldehyde

CHO

HO H

C

CH OH2

CH OH2

H

CHO

HO

CHO

H

C

CH OH2

OH

CH OH2

H

CHO

OH

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Chiral center.Chiral center.

Asymmetric carbon Asymmetric carbon - 4 different things are attached to it.

Cl |

I - C - F |

BrYou must have at least one asymmetric

carbon to have stereoisomers.

Chiral center

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ExamplesExamples

Is the ‘red’ carbon chiral?

H

ClCC=O

CC-OHH

H3C-

H

CC-OH

CH2CH3

H3C-

H

H | C=O | H-CC-OH |

CH2OH

CC=CCl

Br

I

F

H2N-C-C-CC-C-C-SH

H H H

HCl Cl

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Physical propertiesPhysical properties

Optical activityOptical activityability to rotate plane polarized light.

dextrorotatorydextrorotatory - rotate to right

- use + symbol

- usually D isomers

levorotatorylevorotatory - rotate to left

- use - symbol

- usually L isomers

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Plane polarized lightPlane polarized light

Light is passed through a polarized filter.A solution of an optical isomer will rotate the light one direction.

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StereochemistryStereochemistry

Properly drawing enantiomers in 3-D is hard.

Use Fischer ProjectionsFischer ProjectionsSpecific type of formula that designatesthe orientation of groups.


CH2OH

H | C=O | H-C-OH |

CH2OH

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With this system, a tetrahedral carbon atom is represented by two crossed lines.

A horizontal bond to an asymmetric carbon designates bonds in the front plane of the page.

Vertical bonds are behind the plane of the page.

Fischer projectionsFischer projections


CH2OH

H O H OH

H OH

CH2OH

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Some important monosaccharidesSome important

monosaccharides

D-glyceraldehyde Simplest sugarD-glucose Most important in dietD-fructose Sweetest of all sugarsD-galactose Part of milk sugarD-ribose Used in RNA

note that each is a D- enantiomer

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D-glyceraldehydeD-glyceraldehyde

Three carbon sugarAldose sugarTriose sugar

aldotriose

H | C=O | H-C-OH |

CH2OH

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D-glucoseD-glucose

• Glucose is an aldohexose sugar.

• Common names include dextrose, grape sugar, blood sugar.

• Most important sugar in our diet.

• Most abundant organic compound found in nature.

• Level in blood can be as high as 0.1%

C

C

C

C

C

CH 2 OH

OH

OH

H

OHH

HO

H

H

OH

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Carbohydrates in cyclic structures

Carbohydrates in cyclic structures

If optical isomers weren’t enough, sugars also form rings. For many sugars, its the most common form.

hemiacetalhemiacetal - forms from alcohol and aldehyde

hemiketalhemiketal - forms from alcohol and ketone

R OR’’ \ |

C=O + ROH R - C - OH / |

R’ R’

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Intramolecular cyclizationIntramolecular cyclization

Cyclization.Cyclization.Remember - chains can bend and rotate.

C

C

C

CH2OH

C

C

OH

O

H C

C

C

CH2OH

C

C

O

OH

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The -OH group that forms can be above or below the ring resulting in two forms - anomers anomers

and and are used to identify the two forms. are used to identify the two forms.

- OH group is down compared to CH2OH (trans).

- OH group is up compared to CH2OH (cis).

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The and forms are in equilibrium so one form can convert to the other - mutarotation.mutarotation.

Haworth projections can be used to help see and orientations.

O O

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Cyclization of D-glucoseCyclization of D-glucose

-D - glucose-D - glucose

- D - glucose- D - glucose

H

OH

O H

OHOH

H

OHH

OH

CH 2 OH

H

C

C

C

C

C

CH 2 OH

OH

OH

H

OHH

HO

H

H

OH

OH

OH

OHOH

H

H

H

OH

CH 2 OH

H

OH

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Fischer vs. Haworth projectionsFischer vs. Haworth projections

H

OH

O H

OHOH

H

OHH

OH

CH2OH

H

-D-glucose-D-glucose

C

C

C

C

C

OH

H

OHH

HO

H

HO-CH2

H OH

H

O

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Cyclization of D-fructoseCyclization of D-fructose

This can also happen to ketose sugars. CH 2 OHO

OHOH

CH2OH

HOH H

H OH

OH

CH 2 OH O

CH2OH

OHOH

HH

H OH

CH 2 OH

C

C

C

C

CH 2OH

O

H

OH

OHH

H

HO

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D-galactoseD-galactose

• Not found in many biological systems• Common part of lactose - disaccharide

OOH

H

H

OHOHH

OHH

OH

CH2OH

H

C

C

C

C

C

CH2OH

OH

H

H

OHH

HO

HO

H

OH

OOH

H

OHOH

HH

H

OH

CH2OH

H

OH

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D-glucose vs. D-galactoseD-glucose vs. D-galactose

C

C

C

C

C

CH 2OH

OH

OH

H

OHH

HO

H

H

OH O

C

C

C

C

C

CH 2OH

OH

H

H

OHH

HO

HO

H

H

D-glucose D-galactose

Can you find a difference? Your body can!

You can’t digest galactose - it must be converted to glucose first.

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D-riboseD-ribose

An important sugar usedAn important sugar usedin genetic material.in genetic material.

This sugar is not used as an energy source but is a part of the backbone of RNA.

When the C-2 OH is removed,the sugar becomesdeoxyribosedeoxyribose which is usedin the backbone of DNA.


CH2OH

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Reactions of glucose and other monosaccharides

Reactions of glucose and other monosaccharides

Oxidation-Reduction.Oxidation-Reduction. Required for their complete metabolic breakdown.

Esterification.Esterification. Production of phosphate esters.

Amino derivatives.Amino derivatives. Used to produce structural components and glycoprotein.

Glycoside formation.Glycoside formation. Linkage of monosaccharides to form polysaccharides.

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Aldehyde sugars (reducing sugars) are readily oxidized and will react with Benedict’s reagent.

This provides a good test for presence of glucose in urine - forms a red precipitate.

Other testsOther tests - Tollen’s or Fehling’s solutions.

Oxidation-Reduction.Oxidation-Reduction.

H | C=O | + 2 Cu 2+ + 5 OH-

H-C-OH |

CH2OH

O- | C=O | + 2 Cu2O + 3H2O H-C-OH |

CH2OH

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Benedict’s reagentBenedict’s reagent

Benedict'sReagent

0.5% 2%

glucose

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Ketones are not easy to oxidize except ketoses.

Enediol reaction.Enediol reaction.

So all monosaccharides are reducing sugars.

Ketone sugarsKetone sugars

C

C

C

C

C

CH 2 OH

OH

OH

H

OHH

HO

H

H

OH

C

C

C

C

C

CH 2 OH

OH

OH

H

OH

HO

H

H

C

C

C

C

CH2OH

CH 2 OH

OH

OH

H

OH

HO

H

H

OHH

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EsterificationEsterification

Esters are formed by reaction of hydroxyl groups (alcohols) with acids.

The hydroxyl groups of carbohydrates react similarly to alcohols.

R OH C R'O

HOR O C

OR' + H2O+

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EsterificationEsterification

The most important biological esters of carbohydrates are phosphate esters.

Example.Example. Phosphoryl group from ATP forms an ester with D-glucose, catalyzed by kinases.

D-glucose + ATP D-glucose-6-phosphate + ADP

kinase

R OH P OHO

OH+ H2O+HO P OH

O

O - RHO

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Amino derivativesAmino derivatives

The replacement of a hydroxyl group on a carbohydrate results in an amino sugar.

H O

OH

OH

H

H

OHH

OH

CH2OH

HH O

OH

OH

H

H

NH2H

OH

CH2OH

H

-D-glucose -D-2-aminoglucose (glucosamine)

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Amino derivativesAmino derivatives

Uses for amino sugars.Uses for amino sugars.

Structural components of bacterial cell walls.

As a component of chitin, a polymer found in the exoskeleton of insects and crustaceans.

A major structural unit of chondroitin sulfate - a component of cartilage.

Component of glycoprotein and glycolipids.

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Glycoside formationGlycoside formation

or -OH group of cyclic monosaccharide can form link with another one (or more).

glycosidic bond

sugar -O- sugar

oxygen bridge

OH

OH

OHOH

H

H

H

OH

CH2OH

HO H

OH

H

OHOH

H

OH H

OH

CH2OH

H

OH

OH

OH H

H

H

OH

CH2OH

H

O H

OH

H

H

OH H

OH

CH2OH

H

OH

oo

+ H2 O

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Glycosidic bondsGlycosidic bonds

OO

Type is based on the position of the C-1 OH

glycosidic bondglycosidic bond - linkage between a C-1 OH and a C-4 OH

glycosidic bondglycosidic bond - linkage between a C-1 OH and a C-4 OH

bonds bonds

O O

C-4 end can be either up or down dependingon the orientation of the monosaccharide.

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O O

O O bonds bonds bonds bonds

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General format used to describe bond.

OH type carbon# of carbon# of ( or ) first sugar second sugar

As we work through the next few examples this will become clear.

For disaccharidesFor disaccharides - the sugar is either or based on form of the remaining C-1 OH.

( )

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-Maltose-Maltose

Malt sugar. Malt sugar. Not common in nature except in germinating grains.

-D-glucose -D-glucose

OH

OH

H

H

H

OH

CH 2 OH

H

OH

OH OH

H

H

H

OH

CH 2 OH

H

OH

O

-D-glucose and -D-glucose, (1 4) linkage.

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-Maltose-Maltose

It is referred to as -maltose because the unreacted C-1 on -D-glucose is in the position.

OH

OH

H

H

H

OH

CH 2 OH

H

OH

OH OHOH

H

H

H

OH

CH 2 OH

H

OH

O

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-Maltose-Maltose

Uses for Uses for -maltose-maltoseIngredient in infant formulas.Production of beer.Flavoring - fresh baked aroma.

It is hydrolyzed the in body by:

maltose + H2O 2 glucosemaltase

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CellobioseCellobiose

Like maltose, it is composed of two molecules of D-glucose - but with a (1 4) linkage.

H O

OH

H

OHH

OH

CH2OH

H

H

O

H O

H

OHH

OH

CH2OH

H

H

OH

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CellobioseCellobiose

OH

OH

H

H

H

OH

CH 2 OH

H

OH

OH OH

HH

H

OH

CH 2 OH

H

OH

O

H O

OH

H

OHH

OH

CH2OH

H

H

O

H O

H

OHH

OH

CH2OH

H

H

OH

The difference inthe linkage resultsin cellobiose being unusable

We lack an enzymethat can hydrolyzecellobiose.

cellobiose (1 4)

maltose, (1 4)

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LactoseLactose

Milk sugarMilk sugar - dimer of -D-galactose and either the or - D-glucose.

-Lactose-Lactose

OOH

H H

H

H

OH

CH 2 OH

H

OH

OH OH

H

H

H

OH

CH 2 OH

H

OH

O

-D-galactose -D-glucose

(1 4) linkage, disaccharide.

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LactoseLactose

We can’t directly use galactose. It must be converted to a form of glucose.

GalactosemiaGalactosemia - absence of needed enzymes needed for conversion.

Build up of galactose or a metabolite like dulcitol (galactitol) dulcitol (galactitol) causes toxic effects.

Can lead to retardation, cataracts, death.

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LactoseLactose

LactaseLactaseEnzyme required to hydrolyze lactose.

Lactose intoleranceLactose intoleranceLack or insufficient amount of the enzyme.

If lactase enters lowerGI, it can cause gasand cramps.

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SucroseSucrose

Table sugar - most common sugar in all plants.

Sugar cane and beet, are up to 20% by mass sucrose.

Disaccharide of -glucose and -fructose.

(1 2) linkage

CH2OH O

CH2OHH

OH H

H OH

H O

OH

H

H

OHH

OH

CH2OH

H

O

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SucroseSucrose

glucose

fructose

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How sweet it is!How sweet it is!

Sweetness relative

Sugar to sucrose

lactose 0.16 galactose 0.32 maltose 0.33 sucrose 1.00 fructose 1.73 aspartame 180 saccharin 450

Sweetness relative

Sugar to sucrose

lactose 0.16 galactose 0.32 maltose 0.33 sucrose 1.00 fructose 1.73 aspartame 180 saccharin 450

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PolysaccharidesPolysaccharides

Carbohydrate polymersCarbohydrate polymers

Storage PolysaccharidesStorage PolysaccharidesEnergy storage - starch and glycogen

Structural PolysaccharidesStructural PolysaccharidesUsed to provide protective walls or lubricative coating to cells - cellulose and mucopolysaccharides.

Structural PeptidoglycansStructural PeptidoglycansBacterial cell walls

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StarchStarch

Energy storage used by plants

Long repeating chain of -D-glucose

Chains up to 4000 units

AmyloseAmylose straight chainmajor form of

starch

AmylopectinAmylopectin branched structure

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Amylose starchAmylose starch

Straight chain that forms coils (1 4) linkage. Most common type of starch.

OH H

H

OHH

OH

CH2OH

H

OH H

H

OHH

OH

CH2OH

H

O O

OH H

H

OHH

OH

CH2OH

H

OH H

H

OHH

OH

CH2OH

H

O O

O

OO

OO

O

O

OO

OO

O

O

OO

OO

O

O

OO

OO

O

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Amylose starchAmylose starch

Example showing coiled structure - 12 glucose units - hydrogens and side chains are omitted.

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Amylopectin starchAmylopectin starch

Branched structure due to crosslinks.

(1 6) linkageat crosslink

OHH OHH OHH

OH H

HOH

CH2OH

H

OH H

HOH

CH2OH

H

O O

OH H

HOH

CH2OH

H

OH H

H

OHH

OH

CH2OH

H

O O

OH H

H

OHH

OH

CH2OH

H

OH H

H

OHH

OH

CH2OH

H

O O

OH H

H

OHH

OH

CH2OH

H

OH H

H

OHH

OH

CH2

H

O O

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c

GlycogenGlycogen

• Energy storage of animals.• Stored in liver and muscles as granules.• Similar to amylopectin.

(1 6) linkageat crosslink

O

O

O

O

O

O

O

O

O

O

O

O

O

O

c

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CelluloseCellulose

• Most abundant polysaccharide.• (1 4) glycosidic linkages.• Result in long fibers - for plant structure.

OH

H

H

OHH

OH

CH2OH

H

OH

H

H

OHH

OH

CH2OH

H

O

O

OH

H

H

OHH

OH

CH2OH

H

OH

H

H

OHH

OH

CH2OH

H

O

O

OH

H

H

OHH

OH

CH2OH

H O

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H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH HH

NH

CH2OH

H

C OCH3

H OO

HH

OHH

COO-

HO

H O

OH

O

HH

NH

CH2OH

H

C OCH3O

MucopolysaccharidesMucopolysaccharides

These materials provide a thin, viscous, jelly-like coating to cells.

The most abundant form ishyaluronic acid.

Alternating units of N-acetylglucosamine and D-glucuronic acid.

(1 3)

(1 4)

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Structural peptidoglycansStructural peptidoglycans

Bacterial cell walls are composed primarily of an unbranched polymer of alternating units of N-acetylglucosamine and N-acetylmuramic acid.

Peptide crosslinks between the polymer strands provide extra strength - varies based on bacterium.

H O

O H

H

NHH

OH

CH2OH

H

C

CH3

O

H O O

H

H

NHH

OR

CH2OH

H

C

CH3

O

O

CH3

CH

O L-Ala

D-Isoglu

L-Lys

D-Ala

(Gly)5

(Gly)5

R =

crosslink forcrosslink forStaphylococcusStaphylococcusaureusaureus

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GlycoproteinsGlycoproteins

Proteins that carry covalently bound carbohydrate units.

They have many biological functions.

• immunological protection

• cell-cell recognition

• blood clotting

• host-pathogen interaction

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Glycoprotein structureGlycoprotein structure

Carbohydrates only account for 1-30% of the total weight of a glycoprotein.

The most common monosaccharides are

glucoseglucose mannosemannose

galactose galactose fucosefucose

sialic acidsialic acid

N-acetylgalactosamineN-acetylgalactosamine

N-acetylglucosamineN-acetylglucosamine

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Glycoprotein structureGlycoprotein structure

Linking sugars to Linking sugars to proteins.proteins.

O-glycosidic bonds using hydroxyl groups of serine

and threonine

N-glycosidic bonds using side chain amide nitrogen

of asparagine residue

C

C

C H

O

CH3

C H2

C

O

H N

OO

H H

H

NHCOCH3H

OH

CH2OH

H

H O

O H

H

NHCOCH3H

OH

CH2OH

H

poly

pep

tid

e c

hain

threonine

asparagine

1 carbohydrates structure and biological function monosaccharides carbohydrates in cyclic structures...

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