17-1 principles and applications of inorganic, organic, and biological chemistry denniston, topping,...
TRANSCRIPT
17-1
Principles and Applications of Inorganic, Organic, and
Biological ChemistryDenniston, Topping, and Caret
4th ed
Chapter 17
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Power Point to Accompany
17-2
Introduction• Carbohydrates are synthesized by
photosynthesis in plants.
• Grains, cereals, bread, sugar cane
• Glucose is major energy source
• A gram of digested carbohydrate gives about 4 kcal of energy
• Complex carbs are best for diet
• USDA recommends about 58% daily calories from carbs (not simple sugars)
17-3
17.1 Carbohydrate TypesMonosaccharides
E. g. glucose, fructoseone sugar (saccharide) molecule
DisaccharidesE. g. sucrose, lactoseTwo monosaccharides linked
PolysaccharidesE. g. starch, glycogen, celluloseChains of linked monosaccharide units
17-4
17.2 Monosaccharides
polyhydroxy
Aldehydesare aldoses
Ketonesareketoses
3=triose4=tetrose5=pentose6=hexose
Number of carbons
17-5
Three carbon monosaccharides
D-glyceraldehyde
Is an aldotriose
dihydroxy acetone
Is a ketotriose
C
C
O H
CH2OH
OHHCH2OH
C
CH2OH
O
17-6
17.3 Stereoisomers and StereochemistryPrefixes D- and L- in a monosaccharide
name identify one of two isomeric forms.
The isomers (same formula) differ in the spatial arrangement of atoms and are stereoisomers.
The stereoisomers D- and L- glycer- aldehyde are nonsuperimposable
mirror image molecules and are called enantiomers (a subset of stereoisomers).
17-7
Stereoisomers and StereochemistryMolecules that can exist in enantiomeric
forms are said to be chiral.
Chirality in glyceraldehyde is conveyed by a chiral (asymmetric) carbon-one with four different groups attached.
17-8
Glyceraldehyde has a stereocenter (chiral) carbon and thus has two enantiomers (nonsuperimposable mirror image molelcules)
The D isomer has the OH on the stereocenter to the right. The L isomer has the OH on the stereocenter to the left.
C
C
O H
CH2OH
OHH
C
C
O H
CH2OH
HOH
the D isomer the L isomer
Stereocenter:connected tofour different atoms or groups
Mirrorplane
17-9
Optical ActivityEnantiomers are also called optical isomers.
Pasteur, in 1848, showed that enantiomers interact with plain polarized light to rotate the plane of the light in opposite directions. This interaction with polarized light is called optical activity and distinguishes the isomers. It is measured in a device called a polarimeter.
A discussion of plane polarized light follows.
17-10
Polarized Light-1Normal light vibrates in an infinite number of directions perpendicular to the direction of travel. When the light passes through a polarizing filter (Polaroid sunglasses, for example) only light vibrating in one plane reaches the other side of the filter.The diagram on the next slide illustrates this idea. The diagram is of a polarimeter, the instrument used to measure rotation of plain polarized light.
17-11
Polarized Light-2
Light vibration inmany directions
Polarized light vibrating in vertical plane.
polarizerPolarized light planebeing rotated in sampletube.
Rotated beam
Analyzer polaroid
17-12
Optical Activity-againWhen an enantiomer in a solution is placed
in the polarimeter, the plane of rotation of the polarized light is rotated.
One enantiomer always rotates light in a clockwise (+) direction and is said to be the dextrorotatory isomer. The other isomer rotates the light in a counterclockwise (-) direction and is the levorotatory isomer.
Under identical conditions, the enantiomers always rotate light to exactly the same degree but in opposite directions.
17-13
Fischer ProjectionsA Fischer projection uses lines crossing
through a chiral carbon to represent bonds projecting out of the page (horizontal lines) or bonds projecting into the page (vertical lines).
Compare the wedge vs the Fischer pictures below for glyceraldehyde.
CHO
C
CH2OH
OHH
CHO
C
CH2OH
HOH
the D isomer the L isomer
CHO
CH2OH
OHH
CHO
CH2OH
HOH
17-14
The D- and L-SystemMonosaccharides are drawn in Fischer
projections with the most oxidized carbon closest to the top. The carbons are numbered from the top. If the chiral carbon with the highest number has the OH to the right, the sugar is D. If the OH is to the left, the sugar is L.
Most common sugars are in the D form.
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C
C
O H
C
OHH
CH2OH
H OH
CH2OH
C
C
O
OH
C OHH
C
H
H OH
CH2OHD-erythrosean aldotetrose
D-fructosea ketohexose
1
2
3
4
1
2
3
4
5
6
17-16
CHO
C
C
OH
OH
C HOH
C
H
H OH
CH2OH
H
D-glucosean aldohexose
D-galactosean aldohexose
CHO
C
C
OH
OH
C OHH
C
H
H OH
CH2OH
H
These diastereomers are also epimers, they differ in configuration at only one stereocenter (colored dot).
17-17
17.4 Biological MonosaccharidesGlucose is the most important sugar in
the human body. Its concentration in the blood is regulated by insulin and glucagon.
Under physiological conditions, glucose exists in a cyclic hemiacetal form where the C-5 OH reacts with the aldehyde.
Two isomers (anomers) are formed which differ in the location of the OH on the acetal carbon, C-1. (Next slide)
17-18
Cyclic Form for GlucoseThe cyclic form of glucose is shown as a
Haworth projection.O
CH2OH
HH
OHH
OH
OH
HOH
H
OCH2OH
HH
OHH
OH
OH
H O
HH
OCH2OH
HH
OHH
OH
OH
HH
OH
form(alpha)
form(beta)
arrows showelectron movement
Pyranose ring form
Haworth projections
17-19
Cyclic Form for Glucose-cont.Fischer to Haworth projections
- D-glucose
C
C
C
OH
OH
C OHH
C
H
HHOCH2
H
OHH
O
1
2
3
4
5
6
ODraw ring with O at upper right.
OCH2OH
HH
OHH
OH
OH
HOH
H
Groups to the left go up on the Haworth ring.
1
23
6
4
5
17-20
Fructose (Levulose or Fruit Sugar)Found in honey, corn syrup, and sweet
fruits. The sweetest of sugars!
D-fructose
CH2OHCC
OOH
C OHHC
H
OHCH2OH
H
1
2
3
4
5
6
O CH2OHCH2OH
HOHH
OH
O
CH2OH
CH2OH
HOHH
OH
17-21
Galactose ( in lactose/milk sugar)
-D-galactoseamine is a component of the blood group antigens.
-D-galactose
CHOCC
OHOH
COH HC
H
OHCH2OH
H
H
1
2
3
4
5
6
OCH2OH
H
H
OH
H
OH
OH
HOH
H
17-22
RiboseRibose also exists mainly in the cyclic form
OHCCH2OH
H
CHO
CC
H OHH OH
CH2OH
HH
OH
H
OH
O H
OH
-D-riboseDeoxyribose has an H herereplacing the OH
17-23
Reducing Sugars
+ Cu2O (red-orange)
Aldehydes of aldoses are oxidized by Benedict’s reagent, an alkaline copper(II) solution. The blue color fades as reaction occurs and a ppt forms. Test measures glucose in urine.
CC
O H
CH2OHOHH
CC
O O
CH2OHOHH+2 Cu2+
17-24
Reducing SugarsAll monosaccharides and the disac-
charides except sucrose are reducing sugars. Ketoses can isomerize to aldoses.
D-glucose
CHCC
OHOH
C OHHC
H
H OHCH2OH
HO
D-fructose
CH2OHCC
OOH
C OHHC
H
H OHCH2OH
CHCC
OHOH
C OHHC
H
H OHCH2OH
OH
enediol
17-25
A Reduced SugarThe most important reduced sugar is deoxyribose. (In DNA)
CC
O H
CHH
CH OH
OHHCH2OH
D-deoxyribose -D-2-deoxyribose
O OH
H
CH2OH
HH
OH
H
H
17-26
17.5 DisaccharidesThe anomeric OH can react with another
OH on an alcohol or sugar. Water is lost to form an acetal.
O
CH2OH
HH
OHH
OH
OH
H
H
OH
+ CH3 OH
O
CH2OH
HH
OHH
OH
OH
H
H
O CH3
+ H2O
Acetal link: R-O-C-O-R
Acetalcarbon
17-27
Disaccharides: SucroseSucrose is formed by linking D-glucose
with D-fructose (acetal link=1) to give a 1,2 glycosidic link.
CH2
O H
OH H
OH
O H
CH2OH
OHO
CH2OH
HH
OH
H
OH
OH
H
H
1 2
Sucrose is table sugar and is linked to dental caries. It is nonreducing. The glycosidic O is part of an acetal and a ketal.
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Disaccharides: LactoseLactose is formed by joining D-galactose to D-
glucose to give a 1,4 glycoside
O
CH2OH
H
H
OH
H
OH
OH
HH OH
O
CH2OH
HH
H
OH
OH
H
H
O1
-D-galactose
4
-D-glucoseLactose is milk sugar. Lactose intolerance
results from lack of lactase to hydrolyze the glycosidic link of lactose.
17-29
Disaccharides:GalactosemiaIn order for lactose to be used as an
energy source, galactose must be converted to a phosphorylated glucose molecule. When enzymes necessary for this conversion are absent, the genetic disease galactosemia results.
People who lack the enzyme lactase (~20%) are unable to digest lactose and have the condition called lactose intolerance.
17-30
Disaccharides: MaltoseMaltose is formed by linking two -D-glucose
molecules to give a 1,4 glycosidic link.
OH
OCH2OH
HH
H
OH
OH
H
H
O
OCH2OH
HH
OHH
OH
OH
HH
Maltose is malt sugar. It is formed when starch is partly hydrolyzed. It is a reducing sugar due to the free acetal.
17-31
Disaccharides:CellobioseCellobiose is formed by linking two D-
glucose molecules to give a 1,4 glycosidic link. It comes from hydrolyzed cellulose.
OCH2OH
HH
OHH
OH
OH
H H
OHOCH2OH
HH
H
OH
OH
H HO
17-32
17.6 Polysaccharides: CelluloseCellulose is the major structural polymer
in plants. It is a liner homopolymer composed of -D-glucose units linked -1,4. The repeating disaccharide of cellulose is -cellobiose.
Animals lack the enzymes necessary to hydrolyze cellulose. The bacteria in ruminants (eg. cows) can digest cellulose so that they can eat grass, etc.
17-33
Structure of Cellulose
OO
CH2OH
HH
OH
OH
OH
H HOCH2OH
HH
H
OH
OH
H HOO
CH2OH
HH
OH
OH
OH
H H
-(1->4) glycosidic bond
17-34
Polysaccharides: StarchStarches are storage forms of glucose
found in plants.They are polymers of linked glucose.If the links are only 1,4, the polymer is
linear and is called amylose. (Figure on next slide.) Amylose usually assumes a helical configuration with six glucose units per turn.
If the links are both 1,4 and 1,6, the polymer is branched and is called amylopectin. (Figure on next slide.
17-35
Polysaccharides: amylose/amylopectin
amylopectin(-1,6 link)
()
O
OCH2
HH
OH
OH
OH
HH
OHO
CH2
HH
OH
OH
OH
HH
OH
OCH2
HH
OH
OH
OH
HO
HOH
OCH2
HH
OH
OH
OH
HHO
CH2
HH
OH
OH
OH
HH
OHO
CH2
HH
OH
OH
OH
HH
OH
(
amylose(-1,4 links)
()
OHO
CH2
HH
OH
OH
OH
HO
HOH
OCH2
HH
OH
OH
OH
HHO
CH2
HH
OH
OH
OH
HH
OHO
CH2
HH
OH
OH
OH
HH
OH
17-36
Polysaccharides: glycogenThe storage carbohydrate in animals is
glycogen. It is a branched chain polymer like amylopectin but it has more frequent branching (about every 10 residues). Glycogen is stored in liver and muscle cells.
17-37
GlycoproteinsThese materials contain carbohydrate
residues on protein chains. Very important examples of these materials are antibodies-chemicals which bind to antigens and immobilize them.
The carbohydrate part of the glycoprotein plays a role in determining the part of the antigen molecule to which the antibody binds.
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Glycoproteins: 2The human blood groups A, B, AB, and
O depend on the oligosaccharide part of the glycoprotein on the surface of erythrocyte cells. The terminal monosaccharide of the glycoprotein at the nonreducing end determines blood group.
17-39
Glycoproteins: 3
Type Terminal sugar
A N-acetylgalactosamine
B -D-galactose
AB both the above
O neither of the above
O is the “universal donor”
AB is the “universal acceptor”
17-40
The End
Carbohydrates