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Structure of Carbohydrates
O
HO
CH2OH
OH
OH
O
CH2OH
OH
OH
OH
O
O
HO
CH2OH
OH
OH
O—HO
H—O
CH2OH
OH
OH
OH
H2O
Sugars OligosaccharidesPolysaccharides
Properties of Carbohydrates
• Most abundant class of organic molecules
• Source: Photosynthesis• Classification
– Monosaccharides• Stereoisomers• Aldehydes (Aldose) or Ketones (Ketose)• Number of Carbons (ie 3=triose; 6=hexose)• Combined: Aldotriose/Ketotetrose
– Polymers• Oligosaccharides (2- ~20 sugars)• Polysaccharides (> ~20 sugars)
Biological Roles of Carbohydrates
• Energy source• Energy storage• Cell walls• Recognition events
– Between proteins (targeting)– Between cells
• Signalling• Components of other biological
molecules– Antibiotics– Enzyme cofactors– Nucleic Acids
Classes of Monosaccharides
C
C
CH2OH
H O
H OH
CH2OH
C
CH2OH
O
D-Glyceraldehyde Dihydroxyacetone
Aldoses(Aldehydes)
Ketoses(Ketones)
Chirality
C
C
CH2OH
H O
H OH
D-Glyceraldehyde
C
C
CH2OH
H O
OH H
L-Glyceraldehyde
D- versus L- determined by chirality of highest number carbon (from aldehyde or ketone)
Epimers(stereoisomers differing by configuration
of only one of several chiral centers)
C
C
H O
H
C
C
H O
H OH
CH2OH
CHO H
CH OH
CHO H
C
C
H O
H OH
CH2OH
CHO H
CH OH
CH OH
OH
CH2OH
CHO H
CHO H
CH OH
D-Galactose (gal)D-Glucose (glc) D-Mannose (man)
Epimers(stereoisomers differing by configuration
of only one of several chiral centers)
C
C
H O
H
C
C
H O
H OH
CH2OH
CHO H
CH OH
CHO H
C
C
H O
H OH
CH2OH
CHO H
CH OH
CH OH
OH
CH2OH
CHO H
CHO H
CH OH
D-Galactose (gal)D-Glucose (glc) D-Mannose (man)
Enantiomers(mirror images)
C
C
H O
HO H
CH2OH
CH OH
CHO H
CHO H
C
C
H O
H OH
CH2OH
CHO H
CH OH
CH OH
L-GlucoseD-Glucose
Anomers
• Anomeric carbon atom– Most oxidized carbon atom– Shares electrons with 2 oxygen atoms
-configuration has -OH on opposite side of ring from CH2OH group at chiral center that designates D- or L-
Cyclization of D-Fructose(biologically relevant forms)
CH2OH
C
O
H OH
CH2OH
CHO H
CH OH
CHOCH2 CH2OH
OH
OH
OH
HOCH2 OH
CH2OH
OH
OH
O O
D-Fructose -D-Fructose-D-Fructose
Examples of Nomenclature
-D-glucopyranose
-D-fructofuranoseConfiguration of anomeric carbon
Configuration of sugar
Sugarprefix
RingType*not required
Anomeric carbon modification:ose: reducingoside: non-reducing
Cyclization of D-Fructose(biologically relevant forms)
CH2OH
C
O
H OH
CH2OH
CHO H
CH OH
CHOCH2 CH2OH
OH
OH
OH
HOCH2 OH
CH2OH
OH
OH
O O
D-Fructose -D-Fructose-D-Fructose
Figure 8-5
Chair Conformations of -D-glucopyranose
Chair and Boat Forms
Equitorial and Axial Substituents
Steric Crowding: equitorial more stable
Equatorial Axial
Phosphate Esters
OO OH
OH
OH
HO
OH
CH2OPO32–
OH
OH
CH2OPO32–
-D-Fructose-1,6-bisphosphate (Fru-1,6-bisP)
-D-Glucose-6-P (Glc-6-P)
=O3POCH2
CH2OH
C O
CH2OPO32–
C
C OHH
OH
CH2OPO32–
C
C OHH
OH
C OHH
CH2OPO32–
D-Erythrose4-phosphate (E4P)
D-Glyceraldehyde 3-phosphate (G3P)
Dihydroxyacetone phosphate (DHAP)
Deoxy Sugars
O
OH
OH
O
OH
OH
2-Deoxyribose (dRib)
Deoxyribose 5-phosphate (dRib-5-P)[Deoxy--D-ribof uranose 5-phosphate]
HOCH22–O3POCH2
Note: 5-membered ring form is used in biological systems
Sugar Alcohols
C
CH OH
CH2OH
CH OH
CH OH
CH2OH
CH OH
CH2OH
CH OH
CH OH
OH
D-Ribose Ribitol
CH2OH
CH OH
CH2OH
CHO H
CH OH
CH OH
C
C
H O
H OH
CH2OH
CHO H
CH OH
CH OH
D-Glucose Sorbitol
Structure of Glycosides
PolymerizationMonomers(Sugars)
Polymers(Disaccharides)
(Oligosaccharides)(Polysaccharides)
NOTE: linear and branched polymers
Glycosidic Linkages (glycoside)
O
CH2OH
OCH3
OH
OH
HO
Acetal
Stable: no mutarotation
Non-reducing sugar (no free anomeric C atom)
Nomenclature
O
CH2OH
OCH3
OH
OH
HO
O
CH2OH
OH
OH
OH
CH3O
OHOCH2 OCH3
CH2OH
OH
HO
Optional
[Non-reducing][Reducing][Non-reducing]
Methyl--D-Fructofuranoside
4-O-Methyl--D- Glucopyranose
O-Methyl--D-Glucopyranoside
Reducing test
• Free Aldehydes are reductants
• If free to mutarotate sugar is a reductant– Must have only –OH
at anomeric carbon
Cupric oxidebrick-red
precipitate
Cu2O
Sucrose (non-reducing)
O
CH2OH
OH
OH
HOO
OHOCH2
CH2OH
OH
OH
OHOCH2 OH
CH2OH
OH
OH
-D-f ructose
-D-glucopyranosyl-(l __> 2)--D-f ructofuranoside
OR: Glc(α1 β2)Fru
Sucrose
O
CH2OH
OH
OH
HOO
OHOCH2
CH2OH
OH
OH
OHOCH2 OH
CH2OH
OH
OH
-D-f ructose
-D-glucopyranosyl-(l __> 2)--D-f ructofuranoside
OR: Glc(α1 β2)Fru
-Maltose
O
CH2OH
OH
OH
HOO
O
CH2OH
OH
OH
OH
-D-glucopyranosyl-(l __> 4)--D-glucopyranose
Glc(α14)Glc
Nomenclature
1. Recognize individual monosaccharides2. Drop the –se and add root for rings
– 6 member: pyran– 5 member: furan
3. Attach:– ose: can mutarotate– oside: canNOT mutarotate– osyl: not terminal residue
4. Indicate carbon to carbon number linkage (##)
5. Label each residue with D or L and α or β
Oligosaccharides
• Generally complex– Heteropolymers– Branched
• Various Cellular Functions– Receptors– Antigens– Signal transduction– Trafficking
Polysaccharides
• Simpler structures– Homopolymers– Less branching
• Limited Cellular Functions– Structural/Protective– Energy Storage
Functions of Polysaccharides
• Structural - e.g. plant cell walls, cement between cells (animals): • -linkages stable to enzymatic cleavage
• Storage - e.g. glycogen as energy reserves:• -linkages are readily cleaved
• Potential osmotic problem
• Accessibility for energy production -linkages
• Branching
Chitin(1—>4)-linked homopolymer of
N-acetylglucosamine
Exoskeletin of invertebrates (e.g. crustacians, insects, and spiders)
Cell wall (most fungi and some algae)
Glycogen(storage)
Linear: α14Branches: α16
O
CH2OH
HO O
OH
OH
O
O
CH2OH
OH
OH
O
CH2OH
HO O
OH
OH
O
CH2OH
OH
OH
O
CH2
O
OH
OH
O
CH2OH
OH
OH
OHO