Ch. 8: Ch. 8: CarbohydratesCarbohydrates
Ch. 10: Ch. 10: Metabolism (intro)Metabolism (intro)
Ch. 11: Ch. 11: GlycolysisGlycolysis
Ch. 12: Ch. 12: Other pathyways in Other pathyways in carbo. metabolismcarbo. metabolism
Exam: Tues Mar 2ndExam: Tues Mar 2nd
Diseases associated with sugar metabolismDiseases associated with sugar metabolism
4 major classes of biomolecules4 major classes of biomoleculesProteinsProteinsCarbohydratesCarbohydratesFatsFats
Nucleic acidsNucleic acids
Most abundant class of macromolecules on the earth
Ch. 8: Ch. 8: CarbohydratesCarbohydrates
Glucose
Carbohydrate (a.k.a. sugars, saccharide)– (CH2O)n n>3
– Monosaccharide – smallest unit or ‘building blocks’
– Oligosaccharide - disaccharide– Polysaccharide – (more than 20)
Glycoconjugates - linked to protein or lipid
(2-20)
FunctionFunctionEnergy storage and releaseEnergy storage and release
Cell wall and protective coatingsCell wall and protective coatings
Marker mol. on cell surface cell-cell interactionsMarker mol. on cell surface cell-cell interactionsvirus invasion…virus invasion…
Protein function (covalent modification)Protein function (covalent modification)
DNA/RNADNA/RNA
‘‘Hydrate of carbon’Hydrate of carbon’
Polyhydroxyl aldehyde (aldose) or
Polyhydroxyl ketone (ketose)
– Aldotriose• Glyceraldehyde (D or L)
– Ketotriose• Dyhydroxyacetone
D enantiomer predominate in nature
MonosaccharidesMonosaccharides
(CH2O)3
Monosaccharides - Monosaccharides - AldosesAldoses
# Isomers = 2n wheren = # of chiral carbons
Epimers – differ in configuration at only one chiral carbon
Enantiomer
Distant chiral CFrom most oxidized
Not all made in nature
Monosaccharides - Monosaccharides - KetosesKetoses
# Isomers = 2n wheren = # of chiral carbons
Furanose – 5 membered ring, one member O of –OH
Pyranose – 6 membered ring, one member O of –OH
Cyclization - Ring StructuresCyclization - Ring Structures
Similar to:
Optical behavior of monosaccharides in solution suggests that they have an additional chiral center.
Cyclization of MonosaccharidesCyclization of Monosaccharides
Most oxidized CNew chiral C
Cyclization - aldohexoseCyclization - aldohexose
Draw most oxidized carbon (C1 aldose and C2 ketose) on right and number C clockwise
In ring most oxidizes carbon new chiral center (anomeric C)
Transfer information from Fisher projections-OH on right then down in Haworth
-OH on left then up in Haworth
Bulky substituent on highest numbered carbon points up
rapid equilibrium Anomers
Equilibrate in solution
In solution at 31°C– 64% -D-glucopyranose– 36% -D-glucopyranose– Very little in open chain or
furanose form
Cyclization - aldohexoseCyclization - aldohexose
Anomers
Anomers
Hemiacetal
Cyclization - aldopentoseCyclization - aldopentose
Haworthprojection
Anomers
Equilibrium
Anomeric C
““Furanose” ConformationsFuranose” ConformationsNot planar
Rapidly interconvert
““Pyranose” ConformationsPyranose” Conformations
More stable
Whether a ring substituent is Equatorial (same plane) or Axial (above/below) depends on whether C-1 or C-4 is above the ring.
Derivatives of monosaccharides – sugar phosphates
Important in metabolism
alcohol phosphate esters
hemiacetal phosphate
More reactiveNucleic acidNucleic acidmetabolismmetabolism
EnergyEnergymetabolismmetabolism
Derivatives of monosaccharides – deoxy sugars
• replacement of one of the -OH groups with H• Important in DNA
DNARNA
OH
OH
OH
OH
RNA hydrolysis
Derivatives of monosaccharides – amino sugars
• amino groups or an acetylated amino group replaces one of the -OH groups
NeuNAc
Sialic acids: on cell surface glycoproteins
Derivatives of monosaccharides – sugar alcohols
• reduction of carbonyl oxygen, so polyhydroxyl alcohol
Id
glyceraldehyde
Idose ---- Inositol
• derived from aldoses by either the oxidation of C1 or the highest-numbered carbon
• Glucose oxidation : gluconate or glucuronate• gluconate can cyclize under acidic conditions to form a
lactone - intramolecular ester.
Derivatives of monosaccharides – sugar acids
Vitamin C orL-Ascorbic Acid
Primates unable to do this reaction
Common Carbohydrates and their abbreviationsCommon Carbohydrates and their abbreviations
Glycoside Bonds – Glycoside Bonds –
• acetal linkage between the anomeric carbon of a sugar and an alcohol, an amine, or a thiol
• Compounds containing glycoside bonds are called glycosides
if glucose donates the anomeric carbon then glucosides
Glycoside Bonds – DisaccharidesGlycoside Bonds – Disaccharides
Hemiacetals -a reactive carbonyl that can be oxidized.
reducingnon-reducing
non-reducing sugar
No open chain equil
anomer: refers to free C1 OH (In equilibruim)
Glycoside Bonds – Glycoside Bonds – DisaccharidesDisaccharides
epimer
Most abundant disacc. in nature (plants)
• Since mono- and disaccharides are hemiacetals they have a reactive carbonyl that can be oxidized.
• Linear polymer usually one reducing end (free anomeric carbon), one non-reducing end, and all internal monosaccharides are acetals that are not in equilibrium with open chains form.
• Some polymers such as the disaccharide sucrose do not have a reducing end (both anomeric carbons are involved in the gycosidic bond) so non-reducing sugar.
Glycoside Bonds – Glycoside Bonds – Reducing and Non-reducingReducing and Non-reducing
Glycoside Bonds –Glycoside Bonds – OtherOther
Polysaccharides – Glucose Storage
Amylose
Amylopectinand
Glycogen
• Plant starch –
mixture of amylose and amylopectin
• Animals glycogen
No template (ie no gene)
Homoglycans- one type of monosaccharide
100-1000 glucose residues (maltose units)
Amylopectin:branch every 25 residues
Glycogen:branch every 8-12 residues
10% mass of liver
Polysaccharides -Polysaccharides -Starch DegradationStarch Degradation
• Humans digest starch via two enzymes:– α -amylase -
endoglycosidase of α-(1-4) linkages (random)
– debranching enzyme
(cleaves limit dextrans)
• Higher plants have– β- amylase
exoglycosidase of α- (1-4) linkages, releasing the disaccharide maltose Single reducing end
Know how starch is broken down !
Amylose
Polysaccharides – Structure
Humans don’t have -glucosidases
Microbe that live in ruminants do
Plant cell walls, stems and branches
300- 15,000 Glc residues
180 deg rotation
termites
Rigid extended conformationH-bondingForms bundles or fibrils
Cellulose -(1-4) linkage
Polysaccharides – Structure
• Chitin– found in exoskeletons of insects and crustaceans, and in
cell wall of algae and fungi– composed of β- (1-4)linkage of GlcNAc residues.
2nd most abundant organic compound on earth
180 deg rotation
H-bondingAdjacent strands
Glycoconjugates: Glycoconjugates: ProteoglycansProteoglycans
• Glycosaminoglycans have dissaccharide components (repeating)– one sugar is an amino
sugar; e.g. GalNAc, or GlcNAc. The other sugar is usually a uronic acid
• Certain types can be sulfated, etc. They are highly hydrated, and viscous and are excellent lubricants
Fluid of jointsElastic and resistant to compressioncartilage
unbranched
cartilage
heteroglycan
Glycoconjugates: Glycoconjugates: PeptidoglycanPeptidoglycan
Bacteria cell wall, heteroglycans chains linked to peptides
GlcNAc linked to N-acetylmuramic acid (MurNAc) joined by β -(1-4) linkage
Large/rigid molDefines shape of cell
Gram stain +/-
Glycoconjugates - Glycoconjugates - GlycoproteinsGlycoproteins
• O-linked - typically a GalNAc residue linked to the side chain of Ser or Thr, occurs in the golgi
• N-linked-typically a GlcNAc residue linked to the nitrogen of an Asn, occurs in the endoplasmic reticulum
N-linked
Glycoconjugates - Glycoconjugates - GlycoproteinsGlycoproteins
Large amt of structural diversity possible !!
Glycoconjugates - Glycoconjugates - Glycoproteins and blood typesGlycoproteins and blood types
Practice Problems
• Draw the Fisher projections of fructose and show how it can cyclize to form both the α and β anomers of fructopyranose and fructofuranose.
• Draw the disaccharide -D-ribofuranosyl –(1-4)--D-glucopyranose. Is this a
reducing or nonreducing sugar? • Compare and contrast the structures of starch, glycogen
and cellulose.
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