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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