Chapter 22

CarbohydratesCarbohydrates

Carbohydrates Fun Facts:Fun Facts:

Photosynthesis converts more than 100 billion metric tons of CO2 and H20 into carbohydrates annually.

Non-photosynthetic cells can make there own glucose from amino acids, fats and other breakdown products.

Carbohydrates Fun Facts 2Fun Facts 2

Mole Ratios 1C, 2H, 1O Mole Ratios 1C, 2H, 1O Empirical Formula = CHEmpirical Formula = CH22OO

monosaccharides have from 3 to 8 carbons

aldose:aldose: linear sugar with an aldehyde group

ketose:ketose: linear sugar with a ketone group

Carbohydrates Fun Facts 3Fun Facts 3

Three classes of carbohydratesThree classes of carbohydrates MonosaccharidesMonosaccharides

3 to 8 carbons with carbonyl and 3 to 8 carbons with carbonyl and alcohol FGalcohol FG

DisaccharidesDisaccharides 2 monosaccharides connected with a 2 monosaccharides connected with a

ketal or acetal connectionketal or acetal connection PolysaccharidesPolysaccharides

Multiple ketal or acetal connectionsMultiple ketal or acetal connections

Monosaccharides Monosaccharides are

classified by their number of carbon atoms

Hexose

Heptose

Octose

TrioseTetrose

Pentose

FormulaName

C3H6 O3C4H8 O4

C5H1 0O5

C6H1 2O6

C7H1 4O7C8H1 6O8

Monosaccharides And they differ by the type

of carbonyl present Aldehyde Ketone

Monosaccharides There are only two trioses

often aldo- and keto- are omitted and these compounds are referred to simply as trioses

Dihydroxyacetone (a ketotriose)

Glyceraldehyde (an aldotriose)

CHO

CHOH

CH2OH

CH2OH

C=O

CH2OH

Monosaccharides Glyceraldehyde, the simplest

aldose, contains a stereocenter and exists as a pair of enantiomers

CHO

CH OH

CH2OH

CHO

C

CH2OH

HHO

Monosaccharides Fischer projection:Fischer projection: a two dimensional

representation for showing the configuration of tetrahedral stereocenters horizontal lines represent bonds projecting

forward vertical lines represent bonds projecting to

the rearCHO

CH OH

CH2OH

H OHCHO

CH2OH

convert to a Fischerprojection

D,L Monosaccharides Emil Fischer decided on of D- and L-

assignments for the enantiomers of glyceraldehyde D-monosaccharide:D-monosaccharide: the -OH is on the right L-monosaccharide:L-monosaccharide: the -OH is on the left

L-GlyceraldehydeD-Glyceraldehyde

CHOCHO

H OH

CH2OH CH2OH

HHO

[]25 = +13.5°D

[]25 = -13.5°D

D,L Monosaccharides the most common D-tetroses and D-

pentoses

CH2OH

CHO

OHOHH

H

CH2OH

CHO

OHHHO

HH

CH2OH

CHO

OHOHH

OHH

CH2OH

CHO

OHHH

HOHH

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

D,L Monosaccharides the three common D-hexoses

CHO

HOHH

HOOHH

CH2OHOHH

CHO

HOHH

HOHHO

CH2OHOHH

CH2OH

HHOC=O

OHH

CH2OHOHH

D-FructoseD-Glucose D-Galactose

Amino Sugars Amino sugars contain an -NH2 group in

place of an -OH group

CHO

OHOHHNH2

HH

HOH

CH2OH

CHO

OHOHHH

HH

HOH2N

CH2OH

CHO

OHOHHNHCCH3

HH

HOH

CH2OH

OCHO

OHHHNH2

HHOHO

H

CH2OH

4

2

D-Mannosamine(C-2 stereoisomer of D-glucosamine

D-Glucosamine D-Galactosamine(C-4 stereoisomer of D-glucosamine)

N-Acetyl-D-glucosamine

Cyclic Structure Aldehydes and ketones react with

alcohols to form hemiacetalshemiacetals cyclic hemiacetals form readily as five- or six-

membered ring

O-HH

O

CO O

H

H

O O-H

H4-Hydroxypentanal

A cyclic hemiacetal

14

14

redraw to show -OH and -CHO

close to each other

Haworth Projections D-Glucose forms these cyclic

hemiacetalsCHO

OH

H

OH

H

HO

H

H OH

CH2OH

HH OH

HHO

HOH

OH

H

CH2OHO

C

H OH

HHO

HOH

H

CH2OHOH

O

H

OHH OH

HHO

HH

OH

H

CH2OHO

D-Glucose

-D-Glucopyranose (-D-Glucose)

()

()

-D-Glucopyranose (-D-Glucose)

+

anomericcarbon

5

5

1

1

redraw to show the -OH on carbon-5 close to thealdehyde on carbon-1

Haworth Projections a five- or six-membered cyclic hemiacetal

is represented as a planar ring groups lie either above or below the

plane the new carbon stereocenter is called an

anomeric carbonanomeric carbon stereoisomers that differ in configuration

only at the anomeric carbon are called anomersanomers

the anomeric carbon of an aldose is C-1; that of the most common ketoses is C-2

Haworth Projections Terminology of carbohydrate chemistry,

means that the anomeric -OH is on the same side of the ring as the terminal -CH2OH

means that the anomeric -OH is on the side of the ring opposite the terminal -CH2OH

a six-membered hemiacetal ring is called a pyranosepyranose, and a five-membered hemiacetal ring is called a furanosefuranose

Haworth Projections aldopentoses also form cyclic

hemiacetals the most prevalent forms of D-ribose

and other pentoses in the biological world are furanoses

OH ()

H

HOH OH

H HOHOCH2

H

OH ()

HOH H

H HOHOCH2

-D-Ribofuranose(-D-Ribose)

-2-Deoxy-D-ribofuranose(-2-Deoxy-D-ribose)

Haworth Projections D-fructose also forms a five-

membered cyclic hemiacetal

HO

HOCH2 OH

HHO

CH2OH

OHH

H

C=O

CH2OH

HOH

CH2OH

OHH

HO HOH

HOHOCH2

HO HCH2OH

OH

D-Fructose

1

2

5

5

5

1

2

2

()

-D-Fructofuranose(-D-Fructose)

-D-Fructofuranose(-D-Fructose)

()

1

Mutarotation Mutarotation: Mutarotation: the equilibrium

interconversion of - and -anomers in aqueous solution

Chair Conformations Pg 475

Lets leave this out. I will be very happy if you can draw Fisher and Hayworth forms.

Physical Properties Monosaccharides are colorless

crystalline solids, very soluble in water sweetness relative to sucrose:

Carbohydrate

fructose

glucose

galactose

sucrose (table sugar)

lactose (milk sugar)

honey

SweetnessRelative to Sucrose

1.741.000.970.74

0.320.16

Artificial Sweetener

SweetnessRelative to Sucrose

maltose 0.33

saccharin 450acesulfame-K 200aspartame 180

Chemical Properties Monosaccharides

Hemiacetal into acetal – glycosidic bond A glycosidic bond slows mutarotation to snails

pace. Acid is needed to break acetal or ketal

Aldose’s reduce Cu2+, Fe3+, and cold MnO4-

Only works with the linear aldehyde form Hemiacetals are in equilibrium with aldehyde form

Called reducing sugars Glycosides cannot reduce these

Carbonyl can be reduced

Formation of Glycosides Treatment of a monosaccharide with

an alcohol gives an acetal

HH OH

HHO

HOH

OH

H

CH2OHO

CH3OHH

+

-H2O

OCH2OH

H

OH

OCH3H

HOH

OHH

H

OCH2OH

H

OH

HH

HOH

OHH

OCH3

(-D-Glucose)-D-Glucopyranose

Methyl -D-glucopyranoside(Methyl -D-glucoside)

anomeric carbon

+

+

Methyl -D-glucopyranoside(Methyl -D-glucoside)

glycosidicbond

Glycosides a cyclic acetal derived of a

monosaccharide is called a glycosideglycoside the bond from the anomeric carbon to

the -OR group is called a glycosidic glycosidic bondbond

mutarotation is VERY SLOW in a glycoside

glycosides are stable in water and aqueous base, but like other acetals, are hydrolyzed in aqueous acid to an alcohol and a monosaccharide

Oxidation to Aldonic Acids the aldehyde group of an aldose is oxidized

under basic conditions to a carboxylate anion the oxidation product is called an aldonic acidaldonic acid reducing sugarreducing sugar (it reduces the oxidizing

agent)

OCH2OH

HOHO

OHOH

COHHHHOOHH

CH2OHOHH

O HC

OHHHHOOHH

CH2OHOHH

O O-

oxidizingagent

D-GluconateD-Glucose-D-Glucopyranose(-D-Glucose)

basicsolution

Oxidation to Uronic Acids

Enzyme-catalyzed oxidation of the primary alcohol at C-6 of a hexose yields a uronic aciduronic acid enzyme-catalyzed oxidation of D-glucose,

for example, yields D-glucuronic acidCHO

CH2OH

OHHHHOOHHOHH

CHO

COOH

OHHHHOOHHOHH OH

OH

COOHO

HOHO

D-Glucose

enzyme-catalyzedoxidation

D-Glucuronic acid(a uronic acid)

Reduction to Alditols The carbonyl group can be reduced

to a hydroxyl group by NaBH4 and H2/Pd the reduction product is called an alditolalditol

OHOH

HOHO

CH2OHO

CHOOHHHHOOHH

CH2OHOHH

NaBH4

CH2OHOHHHHOOHH

CH2OHOHH

D-Glucitol(D-Sorbitol)

D-Glucose-D-Glucopyranose

Reduction to Alditols sorbitol is found in the plant world in

many berries and in cherries, plums, pears, apples, seaweed, and algae

it is about 60 percent as sweet as sucrose these three alditols are also common in

the biological world

CH2OH

CH2OH

OHHOHH

CH2OH

CH2OH

OHHHHOOHH

CH2OHHHOHHOOHH

CH2OHOHH

D-Mannitol XylitolErythritol

D-Glucuronic Acid D-glucuronic acid exists in the plants and animals in humans, it is an important component of the

acidic polysaccharides of connective tissues it is used to detoxify foreign phenols and

alcohols; in the liver, these compounds are converted to glycosides of glucuronic acid and excreted in the urine

OHOHO

OHO

COO-

HO

Propofol A urine-soluble glucuronide

Phosphate Esters Mono- and diphosphoric esters are

intermediates in metabolism of monosaccharides

the first step in glycolysis is conversion of D-glucose to -D-glucose 6-phosphate

CHO

CH2O-P-O-

OHHHHOOHHOHH

O-

O

CH2

OP O--O

OHO

HO

OHHO

O

D-Glucose 6-phosphate

Disaccharides Sucrose

most abundant disaccharide sucrose is a nonreducing sugar (why)

HOOH

OH

CH2OH

O

OH

HOO

CH2OH

HOCH2

OHO

HO

O

OH

CH2OH

OH

HOO

CH2OH

HOCH2

1

1

2

1

2

1

a unit of -D-glucopyranose

a unit of -D-fructofuranose

Disaccharides Lactose

lactose is the principal sugar present in milk it consists of D-galactopyranose bonded by a -1,4-

glycosidic bond to carbon 4 of D-glucopyranose lactose is a reducing sugar (why)

O

OH

HOOH

O

CH2OH

O

HOOH

OH

CH2OHOOH O

OH

OH

CH2OH

O OH

OH

OH

CH2OH

1

1

4

4

-1,4-glycosidic bond

Disaccharides Maltose

present in malt two D-glucopyranose joined by an -1,4-glycosidic bond maltose is a reducing sugar (Why)

OHO

HOOH

OOHO OH

OH

CH2OH

CH2OHO

OH

O

OHHO

O OH

HO

OH

CH2OH

HOCH2 1

4

-1,4-glycosidicbond

1 4

Polysaccharides Polysaccharide:Polysaccharide: lots of

monosaccharide units Also called glycans Can be or linked anomers

One we can digest “” The other we cannot “”

Polysaccharides - Starch:Starch: an energy storage polymer of D-

glucose found in plants starch can be separated into amylose and

amylopectin amylose is D-glucose units joined by -1,4-

bonds Amylopectin - D-glucose units joined by -

1,4 bonds; at branch points, new chains every 24 to 30 units are started by -1,6-glycosidic bonds

Polysaccharides - GlycogenGlycogen is the energy-reserve

carbohydrate for animals glycogen - glucose units joined by -1,4-

and -1,6-glycosidic bonds (branches occur every 8 to 12 residues - more compact than starch)

the total amount of glycogen in the body of a well-nourished adult human is about 350 g, divided almost equally between liver and muscle

Polysaccharides - Why Store sugar as starch or Why Store sugar as starch or

glycogen?glycogen? Osmolarity

Individual sugars would be 0.4 M Polymers (mostly insoluable) 10-8 M

Cells would burst with water running into the to equilibrate osmotic pressure!

Polysaccharides - CelluloseCellulose is a linear polysaccharide of D-glucose

units joined by -1,4-glycosidic bonds it has an average molecular weight of 400,000 g/mol,

approximately 2200 glucose units cellulose molecules act like stiff rods and align

themselves side by side into well-organized water-insoluble fibers in which the OH groups hydrogen bond with each other rather than water.

this arrangement of parallel chains in bundles gives cellulose fibers their high mechanical strength

it is also the reason why cellulose is insoluble in water

Polysaccharides - Cellulose (cont’d)

animals cannot digest cellulose no contain -glucosidases, enzymes that

catalyze hydrolysis of -glucosidic bonds we have only -glucosidases; hence we can

digest starch and glycogen many bacteria and microorganisms have

-glucosidases and can digest cellulose termites have such bacteria in their

intestines and can use wood as their principal food

Acidic Polysaccharides Acidic polysaccharides:Acidic polysaccharides: contain carboxyl

groups and/or sulfuric ester groups play important roles in the structure and

function of connective tissues there are a large number of highly

specialized forms of connective tissue such as cartilage, bone, synovial fluid, skin,

tendons, blood vessels, intervertebral disks, and cornea

most connective tissues are made up of collagen, a structural protein, in combination with a variety of acidic polysaccharides

Acidic Polysaccharides Hyaluronic acidHyaluronic acid

Found in embryonic tissues, synovial fluid, lubricant of joints in the body, and the vitreous of the eye

O

HOOH

COO-

OHO

NH

CH2OH

CH3C O

O O

The repeating unit of hyaluronic acid

4

13

1

3

4

D-glucuronic acid N-Acetyl-D-glucosamine

Acidic Polysaccharides Heparin: a heterogeneous mixture of

variably sulfonated polysaccharide chains, ranging in molecular weight from 6,000 to 30,000 g/mol

-O3S

OOHO

NH

CH2

OSO3-

O O

HOOH

COO-

OO

ONH

CH2

OH

OO

HO

OSO3-

OOHO

NH

CH2

OSO3-

O

CCH3

O

SO3-

COO-

SO3-

N-acetyl-D-glucosamine

D-glucuronic acid

D-glucosamine

L-iduronic acid

D-glucosamine

Acidic Polysaccharides Heparin (cont’d)

heparin is synthesized and stored in mast cells of various tissues, particularly the liver, lungs, and gut

the best known and understood of its biological functions is its anticoagulant activity

it binds strongly to antithrombin III, a plasma protein involved in terminating the clotting process

End End Chapter 19Chapter 19

Carbohydrates