Chp 1 Carbohydrate

7/31/2019 Chp 1 Carbohydrate

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Key words

Carbohydrate- definition

Aldose, ketose

Classification

Enantiomer, Diastreomer, Epimer

Fischer projection, Haworth projection

CARBOHYDRATE


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Carbohydrates

Carbohydrate: most abundant biomolecules(other biomolecules protein, lipid, nucleic

acid) Suffixose indicates the molecule is a

carbohydrate

- glucose, fructose, maltose, sucrose, cellulose

Major role in energy metabolism and structuralcomponent


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Why Carbohydrates?

Play a number of important roles in

biochemistry:

Major energy sources

Play a key role of processes that take place on

the surfaces of cells. eg. cell-cell interactions

Essential structural components of severalclasses organisms.


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Carbohydrates

Definition: a polyhydroxyaldehyde or

polyhydroxyketone, or a substance thatgives these compounds on hydrolysis


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Carbohydrate

Three level number of sugar/saccharide unit

1. Monosaccharide simplest

2. Oligosaccharide consist more than 1monosaccharide > disaccharide has 2monosaccharide

3. Polysaccharide has large number ofmonosaccharide


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CARBOHYDRATE

MONOSACCHARIDE


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Monosaccharide: simplest carbohydrate,

sometimes referred as sugar / saccharide

Building blocks of all carbohydratesThey have the general formula CnH2nOn, where n

varies from 3 to 8

Aldose: a monosaccharide containing an aldehydegroup

Ketose: a monosaccharide containing a ketone group

Monosaccharides


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Monosaccharides are classified by theirnumber of carbon atoms

- 3 C = triose- 4 C = tetrose

- 5 C = pentose

- 6 C = hexose

- 7 C = heptose

Trioses are simplest carbohydrate

monosaccharides

Monosaccharides


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Aldose: containing an aldehyde group


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Ketose: containing a ketone group


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D-Glucose

This is a Fischer

Formula

6C monomeric

molecule

Is an aldohexose

D to denote theOH

on C5 is on the right

side of the C chain


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Fischer Projections and

Haworth Projections


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Fischer Projections

Fischer projection:bonds

are written in a two

dimensional representation

showing the configurationof tetrahedral stereocenters

horizontal lines represent

bonds projecting forward

vertical lines represent bondsprojecting to the rear

the carbon atom at the

intersection of the horizontal

and vertical lines is not

shown


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Comparison of the Fischer andHaworth Representations


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Glyceraldehyde contains a stereocenter andexists as a pair of enantiomers

Mirror-images stereoisomers are calledenantiomers

Monosaccharides


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Stereochemistry of monosacharides

Anomers :- (carbonyl becomes a new

chiral; C1)

Epimers :- ( excluding the anomeric

carbon )


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Enantiomers :- Molecules that are

superimposible mirror images of one

another.

Isomers : Isomers are molecules with the

same molecular formula, but differentarrangements of atoms.


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Stereoisomers : molecules that differ fromeach other only in their configuration ( three

dimensional shapes )also called optical

isomers. Glucose n Galactose.

Diastereomers :non superimposable,non mirror

image stereoisomers. ( L- Threose with both Dn L erythrose. )


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Stereoisomer

Stereoisomer that are

nonsuperimposable

mirror images of eachother = enantiomer

Chiral carbon/centre =

carbon atom connected to 4different groups

Chiral carbon

Chiral molecule

mirror


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StereoisomerD,L Monosaccharides

What is D and L?

D = dextrorotary, L = levorotary

Are stereoisomers, due to the rotated direction

of plane polarized light of solution

Enantiomers: stereoisomers that are mirror

images

example: D-erythrose and L-erythrose are

enantiomers


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D,L Monosaccharides-Fischer Projections

According to the conventions

proposed by Fischer

D-monosaccharide: a

monosaccharide that, when

written as a Fischer projection,

has the -OH on its penultimate

carbon on the right

L-monosaccharide: a

monosaccharide that, when

written as a Fischer projection,

has the -OH on its penultimate

carbon on the left

REMEMBER: D,L= enantiomers


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D,L Monosaccharides-Fischer Projections

According to theconventions proposed

by FischerD-monosaccharide:has the -OH on itspenultimatecarbon on

the rightL-monosaccharide:

has the -OH on itspenultimatecarbon on

the left

REMEMBER: D,L= enantiomers


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Diastereomers

Diastereomers: stereoisomers that are notmirror

images, non-superimposableexample: D-erythrose and D-threose are diastereomers

Epimers-diastereomer differ at only one chiral carbon

Th ld h hi l C C


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Fig. 16-3, p.437

The aldotetroses have two chiral C ; C-

2 and C-3.

Therefore, the stereoisomers of

aldotetroses are 22, or four possible

stereoisomers.

Diastereoisomers that differ from

each other at only one chiral C are

known as epimers.

D-erythrose and D-threose are

epimers.


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Diastereomers - example


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D-mannose and D-galactose differ

stereochemically from D-glucose at only 1 chiral

center D-mannose and D-galactose areEPIMERS of glucose

D-galactose is a C-4

Epimer of D-glucose

D-mannose is a C-2

Epimer of D-glucose

Epimers - example


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Fructose

Epimers of D-fructose

Enantiomers of D-fructose

Diastrereomer of D-fructose


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Fructose

Which structure represents D-Fructose?


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Lesson outcome

Draw from Fischer to Haworth

Reaction of monosaccharide

Members of disaccharide

Disaccharide formation


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What Happens if a Sugar

Forms a Cyclic Molecule?

Cyclization of sugars takes place due to interactionbetween functional groups on distant carbons, C1 to C5,to make a cyclic hemiacetal - aldose

Cyclization using C2 to C5 results in hemiketalformation.- ketose

In both cases, the carbonyl carbon is new chiral center

and becomes an anomeric carbon


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Formation of a Cyclic

Hemiacetal


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Cyclic Structure

via Haworth Projections Monosaccharides have -OH and C=O

groups in the same molecule and exist

almost entirely as five- and six-memberedcyclic hemiacetals

anomeric carbon: the new stereocenter

resulting from cyclic hemiacetal formationanomers:carbohydrates that differ in

configuration only at their anomeric carbons


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Haworth Projections

Haworth projections

five- and six-membered hemiacetals are represented as

planar pentagons or hexagons, as the case may be,

viewed through the edge

most commonly written with the anomeric carbon on

the right and the hemiacetal oxygen to the back right

the designation -means that -OH on the anomeric

carbon is cis to the terminal -CH2OH; - means that it

is trans


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Haworth Projections

A six-membered hemiacetal ring is shown by

the infix -pyran- (pyranose)

A five-membered hemiacetal ring is shown bythe infix -furan- (furanose)


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CONVERTING A FISCHER PROJECTION TO A HAWORTH

CHO

OH

HO

OH

OH

CH2OH

This -OH

determines

D- or L-

These groups

are down in

the Haworth

These groups

are up in

the Haworth

UP DOWN

This group, whichis carbon 6, will be

up in the Haworth if

D- and down if L-

Carbon 1 will be the

anomeric carbon

CH2OH

OH

OH

OH

OHO

1

23

4

5

6D -

This is the

-anomer because

the anomeric OH is

cisto -CH2OH

down

up

down

cis


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Reaction of Monosaccharides

1. Oxidation-reduction

i. Oxidation of aldoses to acid

ii. Reduction of ribose to deoxyribose

iii. Reduction of L-galactose to L-fucose (L-6deoxygalactose)

iv. Reduction of carbonyl group to hydroxyl groupformingsugar alcohol/alditols

2. Esterification

i. Formation of phosphate esters-intermediate in energymetabolism


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Oxidation

Reducing sugar: a sugar that has a

free carbonyl group (anomeric

carbon) one that can reduces an

oxidizing agent

Tollens reagent oxidizing agent


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Reduction

ribose to deoxyriboseReduction to sugar alcohol/alditols


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Esterification -

Phosphoric Esters Phosphoric esters are particularly important in themetabolism of sugars to provide energy

phosphoric esters are frequently formed by transfer of a

phosphate group from ATP


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Monosaccharide derivatives

Amino sugars


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The most abundance monosaccharide in nature.


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CARBOHYDRATE

DISACCHARIDE


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Glycosidic Bond Formation

Glycosidic bond: form between the hemiacetal ofmonosaccharide (saccharide) and the hydroxyl group of

organic compound such as alcohol.

A substance containing a glycosidic bond is a glycoside

Disaccharide: glycosidic bond formation between thehemiacetal of monosaccharide and hydroxyl group from

another hemiacetal

Glycosidic bond

due to dehydration/condensation


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Glycosidic Bond Formation

Type of bond: O-glycosidic bond


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Two Different Disaccharides of

-D-Glucose

Glycosidic linkagescan take variousforms; the anomeric

carbon of one sugar toany of the -OH groupsof another sugar toform an - or -

glycosidic linkage

Type of bond: O-glycosidic bond


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Disaccharides Sucrose

Table sugar; obtained from the juice of sugar cane and sugar beet

One unit of D-glucose and one unit of D-fructose joined by an -1,2-glycosidic bond

LactoseMade up of D-galactose and one unit of D-glucose joined by a -1,4-glycosidic bond

Galactose is a C-4 epimer of glucose

Maltose

Two units of D-glucose joined by an -1,4-glycosidic bond

Formed from the hydrolysis of starch

Cellobiose

Two units of D-glucose joined by an -1,4-glycosidic bond

Formed from the hydrolysis of cellulose


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Reducing & Non Reducing Sugar

Sugars exist in solution as an equilibrium mixture of open-

chain and closed-ring (or cyclic) structures.

In the open-chain form, the carbon atom that contains theC=O bond is called the carbonyl carbon.

Sugars that can be oxidised by mild oxidising agents such

as Benedict's Solution, Fehling's Solution,and Tollen's

Reagen are called reducing sugars because the oxidisingagent is reduced in the reaction.

Reducing sugar: one that has a free aldehyde group and

this aldehyde is easily oxidized.


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+ Ag (NH3)2Beingreduced

Tollens agent


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Haworth Projections

Anomeric

carbon

IfOH is free at theanomeric carbon =the monosaccharideis reducing sugar


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Sucrose

Anomeric carbons of glucose carbon C1 in configuration is linked to the anomeric carbon offructose C2 in configuration

anomeric carbon is tied into aglycosidic bond and none of it

able to form an open chain

containing free aldehyde and

ketone sucrose is NOT a

reducing sugar


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Lactose

Galactose in a (1-4) linkage with glucose

Principal sugar present in milk

Galactose is converted by the body to glucose and glucose usedfor energy

Reducing sugar?


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Maltose

Products from hydrolyticbreakdown of starch

Can be easily digested

by humans because ofthe presence of enzymescatalyzes the hydrolysisof (1-4) glycosidic

bonds

Reducing sugar?


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Cellobiose

Cellobiose hydrolysis product of cellulose

major component of plants

Differs from maltose at glycosidic bond

Humans do not have the capacity to

digest cellobiose or cellulose lack

the enzyme cellulase that break (1-4)

glycosidic linkages between glucose

monomers

Ruminants animals can have

bacteria in the rumen in gastrointestine

tract and secrete cellulase


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N-glycosidic bond

The -NH group of amine

substitute for hydroxyl groups

and react at the anomeric

carbon center of

carbohydrates.

New linkage is called N-

glycosidic bond Importance in the construction

ATP and in nucleic acids RNA

and DNA

ATP


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Disaccharides

Formation of glycosidic bondcondensation (-H2

O)


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CARBOHYDRATE

POLYSACCHARIDE


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Key words

Definition

Function

Homopolysaccharide andheteropolysaccharide

Cellulose, Chitin, Pectin, Peptidoglycan

Starch, glycogen

Glycoaminoglycan, glycoprotein


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Polysaccharides

Polysaccharide- When many monosaccharides

are linked together

Divided into 2type of monosaccharide orfunction

Two main function: energy storage and structure

Type of monosaccharidehomopolysaccharideand heteropolysaccharide


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Structural Polysaccharides

Cellulose

PectinChitincomponent of the exoskeleton

of invertebrates and in cell walls of

algae, fungi and yeast

Plant cell wall


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Cellulose

the major structural component of plants,

especially wood and plant fibers

a linear / unbranched polymer of approximately 2800-D-glucose units joined by

extensive intra- and intermolecular hydrogen bonding

between chains-strength

Cellobiose is the repeating

hydrolysis by cellulase


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Cellulose


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Cellulose

Cellulose is a

Structural

polysaccharide

Polymeric Structure of Cellulose


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Polymeric Structure of Cellulose


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Pectin

Important component of

plant cell walls

MonomerD-Galacturonicacid, derivative of galactose

Commercially important-

food processing industry- as gelling agent in jams

and jellies


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Chitin

the major structural component of the

exoskeletons of invertebrates and crustaceans; and

in cell walls of algae, fungi, and yeasts -1,4-glycosidic bondssimilar with cellulose

linear polymer, each chain held together by

hydrogen bonds

composed of units ofN-acetyl--D-

glucosaminediffer with cellulose


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Chitin

Differ with glucose


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Peptidoglycan

Bacterial cell walls:

prokaryotic cell

walls are constructedon the framework of

the repeating unit

NAM-NAG joined

by Presence ofpeptide

bond


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Storage Polysaccharides

Starch

Glycogen


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Starch

Starch is used for energy storage in plants

amylose: continuous, unbranched chains of up to 4000 -D-glucose units joined by

amylopectin: a highly branched polymer consisting of 24-30 unitsofD-glucose joined by and branches created by

amylases catalyze hydrolysis of-1,4-glycosidic bonds

*-amylase is an exoglycosidase and cleaves from the nonreducingend of the polymer

*-amylase is an endoglycosidase and hydrolyzes glycosidiclinkages anywhere along the chain to produce glucose and maltose

debranching enzymes catalyze the hydrolysis of-1,6-glycosidicbonds

Starch


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Starch


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Amylose and Amylopectin


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Amyloseoccurs as a helixwith 6 residues per turn- able to give the dark-blue colorcomplex with iodine.


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Glycogen

Glycogen is used for energy storage in animals

Has amylose and amylopectinsimilar to starch

Differ with starchthe amylopectin is highly branched

- branch point: occur about every 10 residues

in starch, about

every 25 residues


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Polysaccharides

Homopolysaccharide: consists of one type of

monosaccharide

Heteropolysaccharide: consists of more than

one type of monosaccharide


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Polysaccharides

H t l h id


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Heteropolysaccharide:

Glycosaminoglycans

Glycosaminoglycans: polysaccharides based on a

repeating disaccharide where one of the monomers

is an amino sugar and the other has a negative

charge due to a sulfate or carboxylate group

Heparin: natural anticoagulant

Hyaluronic acid: a component of the vitreous humor

of the eye and the lubricating fluid of joints Chondroitin sulfate and keratan sulfate: components

of connective tissue

H t l h id


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Heteropolysaccharide:

Glycosaminoglycans


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Glycoproteins

Glycoproteins contain carbohydrate units covalentlybonded to a polypeptide chain

antibodies are glycoproteins

Oligosaccharide portion of glycoproteins act as antigenicdeterminants

Among the first antigenic determinants discovered were the bloodgroup substances

In the ABO system, individuals are classified according to fourblood types: A, B, AB, and O

At the cellular level, the biochemical basis for this classification isa group of relatively small membrane-bound carbohydrates


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QUIZ

1. Give two important functions of polysaccharide.

2. Name 2 structural polysaccharide and 2 storagepolysaccharide.

3. Give one example of heteropolysaccharide.

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Chp 1 Carbohydrate