I.2 Carbohydrates

7/28/2019 I.2 Carbohydrates

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© 2003 Thomson Learning, Inc.

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Functional Groups are:

• Groups of atoms that give properties tothe compounds to which they attach

Gained Electrons Lo st Electrons



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Common Functional Groups



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Macromolecules

Macromolecules

Macromolecules are formed by a process known as

polymerization.

Monomers

Polymers



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Giant Molecules - Polymers

•

Large moleculesare called polymers

Polymers are built

from smaller molecules called

monomers

Biologists call them

macromolecules



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Examples of Polymers

•Proteins

Lipids

Carbohydrates

Nucleic Acids



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Most Macromolecules arePolymers

•Polymers are made by stringing togethermany smaller molecules calledmonomers

Nucleic Acid Monomer



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Linking Monomers

Cells link monomers by a process called condensation or dehydration synthesis (removing a molecule of water)

This process joins two sugar monomers to make a double sugar

Remov

e H

Remove OH

H 2 O Forms



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Breaking Down Polymers

• Cells breakdownmacromolecule

s by a processcalledhydrolysis(adding amolecule ofwater)

Water added to split a double sugar



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Macromolecules in Organisms

• There are four categories of largemolecules in cells:

Carbohydrates

Lipids

Proteins

Nucleic Acids



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Carbohydrates



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Carbohydrates• Carbohydrate: (also called as sugars)

• General formula can all be written in a simpleform as (CH2O)x

• a polyhydroxyaldehyde or polyhydroxyketone, or

a substance that gives these compounds onhydrolysis

• Rooted in the word “saccharide” (from the Latin,

saccharum, meaning sugar).

• Simple units of sugar are calledmonosaccharides

• Can be linked together to form disaccharides,

oligosaccharides and polysaccharides



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Functions• For Energy

• Used as fuel by our bodies

• For Structural Support

• As roughage or fiber in the diets and is importnat forintestinal health

• As structural component of plant in their cell walls

• As structural component component exoskeleton ofarthropods

•

For Cell Identification• Embedded into the surface of cell membranes as

glycolipids and glycoproteins



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Classes• Monosaccharides

• Disaccharides

• Polysaccharides



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Classification• Monosaccharide: a carbohydrate that cannot be

hydrolyzed to a simpler carbohydrate• they have the general formula CnH2nOn, where n varies

from 3 to 8

• aldose: a monosaccharide containing an aldehyde

group

• ketose: a monosaccharide containing a ketone group



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Monosaccharides• Monosaccharides are classified by their number

of carbon atoms

hexose

heptose

octose

triose

tetrose

pentose

FormulaName

C3 H6 O3

C4 H8 O4

C5 H1 0 O5

C6 H1 2 O6

C7 H1 4 O7

C8 H1 6 O8



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Monosaccharides• There are only two trioses

• aldo- and keto- are often omitted and these compoundsare referred to simply as trioses; although thisdesignation does not tell the nature of the carbonylgroup, it at least tells the number of carbons

Dihydroxyacetone(a ketotriose)Glyceraldehyde(an aldotriose)

CHO

CHOH

CH2 OH

CH2 OH

C= O

CH2 OH



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Monosaccharides• Glyceraldehyde contains a stereocenter and

exists as a pair of enantiomers

L-GlyceraldehydeD-Glyceraldehyde

CHO

C

CHO

CH OH

CH2 OH CH2 OH

HHO



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Fischer Projections• Fischer projection: a two dimensional

representation for showing the configuration oftetrahedral stereocenters

• horizontal lines represent bonds projecting forward

• vertical lines represent bonds projecting to the rear

• the carbon atom at the intersection of the horizontaland vertical lines is not shown

D-Glyceraldehyde

CHO

CH OH

CH2 OH

D-Glyceraldehyde

convert toa Fischer

projection H OH

CHO

CH2 OH



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D,L Monosaccharides• According to the conventions proposed by

Fischer• D-monosaccharide: a monosaccharide that, when

written as a Fischer projection, has the -OH on itspenultimate carbon on the right

• L-monosaccharide: a monosaccharide that, whenwritten as a Fischer projection, has the -OH on itspenultimate carbon on the left



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The four aldotetroses• Enantiomers: stereoisomers that are mirror

images• example: D-erythrose and L-erythrose are enantiomers

• Diastereomers: stereoisomers that are not mirror

images• example: D-erythrose and D-threose are diastereomers

CHO

CH2 OH

OHH

OHH

CHO

CH2 OH

HHO

HHO

CHO

CH2 OH

HHO

OHH

CHO

CH2 OH

OHH

HHO

D-Erythrose L-Erythrose D-Threose L-Threose

Mirrorplane

Mirrorplane



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• Following are the two most common D-

aldotetroses and the two most common D-aldopentoses

D,L Monosaccharides

D-Erythrose D-Threose D-Ribose 2-Deoxy-D-ribose

CHO

CH2 OH

OHH

OHH

CHO

CH2 OH

HHO

OHH

CHO

CH2 OH

OHH

OHH

OHH

CHO

CH2 OH

HH

OHH

OHH



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D,L Monosaccharides• and the three most common D-aldohexoses. Note that

the third of these is an amino sugar• also shown is the most common 2-keto-D-hexose

CHO

CH2 OH

OHH

HHO

OHH

OHH

D-GlucosamineD-Glucose D-Galactose

CHO

CH2 OH

OHH

HHO

HHO

OHH

CHO

CH2 OH

N H2H

HHO

OHH

OHH

CH2 OH

C

CH2 OH

O

HHO

OHH

OHH

D-Fructose



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Cyclic Structure• Monosaccharides have -OH and C=O groups in

the same molecule and exist almost entirely asfive- and six-membered cyclic hemiacetals

• anomeric carbon: the new stereocenter resulting fromcyclic hemiacetal formation

• anomers: carbohydrates that differ in configurationonly at their anomeric carbons



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Haworth Projections• Haworth projections

• five- and six-membered hemiacetals are represented asplanar 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 istrans



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Haworth Projections

D-Glucose

-D-Glucopyranose(-D-Glucose)

C

H OH

HHO

HOH

H

CH2 OH

OH

OH( )

H OH

HHO

HH

OH

HCH2 OH

O

O

H

H

H OH

HHO

HOH( )

OH

HCH2 OH

O

-D-Glucopyranose

(-D-Glucose)

+

anomericcarbon

5

5 5

5

CH= O

CH2 OH

OHH

HHO

OHH

OHH

redraw



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Haworth Projections• a six-membered hemiacetal ring is shown by the infix -

pyran-• a five-membered hemiacetal ring is shown by the infix -

furan-

OOPyranFuran



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Conformational Formulas• five-membered rings are so close to being planar that

Haworth projections are adequate to representfuranoses

O

OH( )

H

HHO OH

H H

-D-Ribofuranose

(-D-Ribose)

O

H

OH( )

HHO OH

H H

-D-Ribofuranose(-D-Ribose)

HOCH2 HOCH2



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Conformational Formulas• for pyranoses, the six-membered ring is more

accurately represented as a strain-free chairconformation

-D-Glucopyranose

(chair conformation)

OCH2 OH

HOHO

OH OH( )



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Conformational Formulas• if you compare the orientations of groups on carbons

1, 2, 3, 4, and 5 in the Haworth and chair projections of-D-glucopyranose, you will see that in each case theyare up-down-up-down-up respectively

-D-Glucopyranose

(chair conformation)

OCH2 OHHOHO

OHOH( )

-D-Glucopyranose(Haworth projection)

H

H OH

HHO

H OH( )OH

H

CH2 OH

O5

51

1

4

4

22 33



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Ascorbic Acid (Vitamin C)• L-Ascorbic acid (vitamin C) is synthesized both

biochemically and industrially from D-glucoseCHO

CH2 OH

OHH

HHO

OHH

OHH

D-Glucose

CH2 OH

OHH

HHO

O

OH

both biochemialand industrial

syntheses

L-Ascorbic acid(Vitamin C)

O



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Ascorbic Acid (Vitamin C)• L-Ascorbic acid is very easily oxidized to L-

dehydroascorbic acid• both are physiologically active and are found in most

body fluids

CH2 OH

OHH

HO

O

O

L-Ascorbic acid

(Vitamin C)

L-Dehydroascorbic acid

oxidation

reduction

CH2 OH

OHH

HHO

O

OH

O O



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Oxidation• Reducing sugar: one that reduces an oxidizing

agent• oxidation of a cyclic hemiacetal form gives a lactone

• when the oxidizing agent is Tollens’ solution, Ag

precipitates as a silver mirror

OH-

H OH

HHO

HOH

H

CH2 OH

O

O

A lactone(a cyclic ester)

OH

H OH

HHO

HH

OH

H

CH2 OH

O

A cyclichemiacetal

A g ( N H3 ) 2++ A g+



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Reduction• The carbonyl group of a monosaccharide can be

reduced to an hydroxyl group by a variety ofreducing agents, including H2/M and NaBH4

• reduction of the C=O group of a monosaccharide givesa polyhydroxy compound called an alditol

Ni+

D-Glucitol(D-Sorbitol)

D-Glucose

H2

CHO

CH2 OH

OHH

HHO

OHH

OHH

CH2 OH

CH2 OH

OHH

HHO

OHH

OHH



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Phosphoric Esters• Phosphoric esters are particularly important in

the metabolism of sugars• phosphoric esters are frequently formed by transfer of

a phosphate group from ATP

H

H OH

HHO

HOH

OH

H

CH2 OH

O

-D-glucose

-O- P-OPOPO-AdenosineO

O- O-

O

O-

O+

+ - OPOPO-Adenosine

O-

O

O-

O

ATP

H

H OH

HHO

H OHOH

H

CH2 OPO32 -

O

-D-glucose-6-phosphate

AD P

enzyme



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Formation of Glycosides• Glycoside: a carbohydrate in which the -OH of

the anomeric carbon is replaced by -OR• those derived from furanoses are furanosides; those

derived from pyranoses are pyranosides

• glycosidic bond: the bond from the anomeric carbon to

the -OR group

O

CH2 OH

H

OH

HH

HOH

OHH

OCH3

Methyl -D-

glucopyranoside

O

CH2 OH

H

OH

HH

HO H

OHH

OH

+ CH3

OH+ H2 O

glycosidicbond

-D-glucopyranose



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Amino Sugars

O

CH2 OH

OH

OH

HO

NH-C-CH3

N-Acetyl-D-glucosamine

OCH2 OH

HOHO

N H

OH

C

CH3

O

O

CH2 OH

O

OH

HO

NH-C-CH3CH3 -CH

O O

OCH2 OH

HOO

N H

OH

C

CH3

O

CH3

-CH

COO-

N-Acetylmuramic acid

COO-

H

HH

H

H

H

HH

H

H



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Common monosaccharides• Glucose

• Dextrose, blood sugar

• Lone energy source of the brain

• Fructose

•

Sweetest natural monosaccharides• Found in fruits, nectar, honey

• Galactose

• Found in milk sugar (lactose)



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Disaccharides and Polysaccharides

• Formed by joining together monosaccharides viacondensation reaction

• A condensation reaction always yields a complex

molecule plus water• Bond linking together is called glcosidic bond

• Disaccharieds and polysaccharides are degradedvia hydrolysis reaction, characterized by

breaking of glycosidic bond by water



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Disaccharides• Sucrose

• table sugar; obtained from the juice of sugar cane andsugar beet

• one unit of D-glucose and one unit of D-fructose joinedby an -1,2-glycosidic bond

OHO

HO

O

OH

CH2 OH

OH

HOO

CH2 OH

HOCH2

1

1

2

O

HO

OH

OH

CH2 OH

O

OH

HOO

CH2 OH

HOCH2

1

2

1

-1,2-glycosidic

bond

D-Glucose

D-Fructose

3



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Disaccharides• Lactose

• about 5% - 8% in human milk, 4% - 5% in cow’s milk • one unit of D-galactose and one unit of D-glucose

joined by a -1,4-glycosidic bond

O

HO

HO

OH

O

CH2 OH

O

HO OH OH

CH2 OHOHO O

HO

OH

CH2 OH

O OH

OH

OH

CH2 OH

1

1

4

4

-1,4-glycosidic bond


D-galactose

D-glucose

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Disaccharides• Maltose

• two units of D-glucose joined by an -1,4-glycosidicbond

OHO

HOOH

OOHO OH

OH

CH2

OH

CH2 OH

O

OH

O

OHHO

OOH

HO

OH

CH2

OH

HOCH2 1

4


1 4

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• Cellulose: the major structural component of

plants, especially wood and plant fibers• a linear polymer of approximately 2800 D-glucose units

per molecule joined by -1,4-glycosidic bonds

• fully extended conformation with alternating 180° flips

of glucose units• extensive intra- and intermolecular hydrogen bonding

between chains

Polysaccharides

O

OHHO

O OO

OH

HO O O

OHHO

HO- CH 2

HO- CH 2HO- CH 2

1

1

1

4

4

4

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Polysaccharides• Starch is used for energy storage in plants

• a polymers of -D-glucose units• amylose: continuous, unbranched chains of up to 4000-D-glucose units joined by -1,4-glycosidic bonds

• amylopectin: a highly branched polymer consisting of

24-30 units of D-glucose joined by -1,4-glycosidicbonds and branches created by -1,6-glycosidic bonds

• amylases catalyze hydrolysis of -1,4-glycosidic bonds

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

glycosidic bonds

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PolysaccharidesFigure 13.22 Branching in amylopectin and glycogen

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Polysaccharides• Glycogen: Used for energy storage in animals

• Composed of D-glucose monomers linked by -1,4-glycosidic bonds and branches created by -1,6-glycosidic bonds

• More highly branched than amylopectin every 12-16

glucose units• Stored in muscles and liver cells

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P l h id



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Polysaccharides• Chitin: the major structural component of the

exoskeletons of invertebrates, such as insectsand crustaceans; also occurs in cell walls ofalgae, fungi, and yeasts

• composed of units of N-acetyl--D-glucosamine joined

by -1,4-glycosidic bondsCHO

CH2 OH

NH-CCH3H

HHO

HHO

OHH

O

N-Acetyl-D-glucosamine

(insert bottom of Fig 13.23)

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Polysaccharides• Bacterial cell walls: prokaryotic cell walls are

constructed on the framework of the repeatingunit NAM-NAG joined by -1,4-glycosidic bonds

O

N HO

O

CH2 OH

O

O

N HHO

CH2 OH

O

O= C O= CCH3 CH3

CHH3 C

COO-

N-Acetyl-D-glucosamine(NAG)

N-Acetylmuramic acid(NAM)

1

4

13

C



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Bacterial Cell Walls• The NAM-NAG polysaccharide is in turn cross-

linked by small peptides• in Staphyloco ccu s aureus , the cross link is a

tetrapeptide

• this tetrapeptide is unusual in that it contains two

amino acids of the D-series, namely D-Ala and D-Gln• each tetrapeptide is cross linked to an adjacent

tetrapeptide by a pentapeptide of five glycine units

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B i l C ll W ll



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O

N HOO

CH2 OH

O

O

NHO

CH2 OH

O

O= C O= CCH3 CH3

CHH3 C

C= O

N H

A la

Gln

Ly s

A la

L

D

L

D

C= O

N H-( Gly) 5 C----

( CH2 ) 4N H- C-( Gly ) 5 - N H - - - - -

To tetrapeptideside chains

O

O

Bacterial Cell Walls

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B i l C ll W ll



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Bacterial Cell WallsFigure 13.24(d) The peptidoglycan of a bacterial cell wall

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Pl C ll W ll



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Plant Cell Walls• consist largely of cellulose

•also contain pectin whichfunctions as an intercellularcementing material

• pectin is a polymer of D-

galacturonic acid joined by-1,4-glycosidic bonds

• the major nonpolysaccharideof cell walls, especially inwoody plants, is lignin (nextscreen)

4

O

OHHO

OCOOH

O

O

OHHO

COOH

O

1

-1,4-glycosidic

bond

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Pl C ll W ll Li i



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Plant Cell Walls - LigninFigure 13.25 Lignin

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Polysaccharides• Glycosaminoglycans: polysaccharides based on

a repeating disaccharide where one of themonomers is an amino sugar and the other has anegative charge due to a sulfate or carboxylategroup

• heparin: natural anticoagulant

• hyaluronic acid: a component of the vitreous humor ofthe eye and the lubricating fluid of joints

• chondroitin sulfate and keratan sulfate: components ofconnective tissue

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H l i A id



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Hyaluronic Acid

O

HO

OH

COO-

OHO

N H

CH2 OH

CH3 C O

O O

The repeating unit of hyaluronic acid

1

3

1

4

D-glucuronic acid N-Acetyl-D-glucosamine

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H i



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Heparin

OO

HON H

CH2

OSO3-

OO

HOOH

COO-

OOO

N H

CH2

OH

OO

HO

OSO3-

OO

HON H

CH2

OSO3-

O

CCH3

O

-O3 S

COO-

-O3 SA pentasaccharide repeating unit of heparin

N-acetyl-D-glucosamine

D-glucuronic acid

-O3 S

D-glucosamine

L-iduronic acid

D-glucosamine

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Gl t i



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Glycoproteins• Glycoproteins contain carbohydrate units

covalently bonded to a polypeptide chain• antibodies are glycoproteins

• carbohydrates play a role as antigenic determinants,the portions of the antigenic molecule that antibodies

recognize and to which they bond

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Bl d G S b t



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Blood Group Substances• Membranes of animal plasma cells have large

numbers of relatively small carbohydrates boundto them

• these membrane-bound carbohydrates act as antigenicdeterminants

• among the first antigenic determinants discoveredwere the blood group substances

• in the ABO system, individuals are classified accordingto four blood types: A, B, AB, and O

• at the cellular level, the biochemical basis for thisclassification is a group of relatively small membrane-bound carbohydrates

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ABO Bl d Cl ifi ti



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ABO Blood Classification• in type A, the nonreducing end is NAGal

•in type B it is Gal

• in type AB, both types are present

• in Type O, neither of these terminal residues is present

NAGal Ga l N AGluCell membraneof erythrocyte

-1,4-) -1,3-) -1-)

Fuc

-1,2-)

NAGal = N-acetyl-D-galactosamineGal = D-galactoseNAGlu = N-acetyl-D-glucosamineFuc = L-fucose

missing intype O blood

D-galactose in

type B blood

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L F



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L-Fucose• L-fucose is synthesized biochemically from D-

mannose

CHO

OH

CH3

HHO

OHH

H

HHO

An L-monosaccharidebecause this -OH is onthe left in the Fischerprojection

rather than -CH2OH

Carbon 6 is -CH 3

L-Fucose

Documents

I.2 Carbohydrates