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.