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4 major classes of biomolecules Proteins Carbohydrates Fats Nucleic acids Ch. 8: Carbohydrates Ch. 10: Metabolism (intro) Ch. 11: Glycolysis Ch. 12: Other pathyways in carbo. metabolism Diseases associated with sugar metabolism Exam: Tues Mar 2nd Ch. 8: Carbohydrates Most abundant class of macromolecules on the earth Glucose Carbohydrate (a.k.a. sugars, saccharide) – (CH2O)n n>3 ‘Hydrate of carbon’ – Monosaccharide – smallest unit or ‘building blocks’ (2-20) – Oligosaccharide - disaccharide – Polysaccharide – (more than 20) Glycoconjugates - linked to protein or lipid Function Energy storage and release Cell wall and protective coatings Marker mol. on cell surface cell-cell interactions virus invasion… Protein function (covalent modification) DNA/RNA Monosaccharides Polyhydroxyl aldehyde (aldose) or Polyhydroxyl ketone (ketose) (CH2O)3 – Aldotriose • Glyceraldehyde (D or L) – Ketotriose • Dyhydroxyacetone D enantiomer predominate in nature Monosaccharides - Aldoses # Isomers = 2n where n = # of chiral carbons Enantiomer Distant chiral C From most oxidized Epimers – differ in configuration at only one chiral carbon Not all made in nature Monosaccharides - Ketoses # Isomers = 2n where n = # of chiral carbons Cyclization - Ring Structures Optical behavior of monosaccharides in solution suggests that they have an additional chiral center. Furanose – 5 membered ring, one member O of –OH Pyranose – 6 membered ring, one member O of –OH Similar to: Cyclization of Monosaccharides Most oxidized C New chiral C Cyclization - 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 Cyclization - aldohexose Anomers Equilibrate in solution In solution at 31°C – 64% b-D-glucopyranose – 36% a-D-glucopyranose – Very little in open chain or furanose form Anomers Cyclization - aldopentose Equilibrium Anomeric C Hemiacetal Haworth projection Anomers “Furanose” Conformations Not planar Rapidly interconvert “Pyranose” 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 Nucleic acid metabolism Energy metabolism hemiacetal phosphate More reactive Derivatives of monosaccharides – deoxy sugars • replacement of one of the -OH groups with H • Important in DNA RNA DNA 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 glyceraldehyde Id Idose ---- Inositol Derivatives of monosaccharides – sugar acids • 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. Primates unable to do this reaction Vitamin C or L-Ascorbic Acid Common Carbohydrates and their abbreviations 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 – Disaccharides No open chain equil non-reducing reducing Hemiacetals -a reactive carbonyl that can be oxidized. b anomer: refers to free C1 OH (In equilibruim) non-reducing sugar Glycoside Bonds – Disaccharides epimer Most abundant disacc. in nature (plants) Glycoside Bonds – Reducing and Non-reducing • 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 – Other Polysaccharides – Glucose Storage • Plant starch – mixture of amylose and amylopectin • Animals glycogen Homoglycans- one type of monosaccharide Amylose 100-1000 glucose residues (maltose units) Amylopectin and Glycogen Amylopectin: branch every 25 residues Glycogen: branch every 8-12 residues 10% mass of liver No template (ie no gene) Polysaccharides -Starch Degradation Know how starch is broken down ! • Humans digest starch via two enzymes: – α -amylase endoglycosidase of α-(14) linkages (random) – debranching enzyme (cleaves limit dextrans) • Higher plants have – β- amylase exoglycosidase of α- (14) linkages, releasing the disaccharide maltose Single reducing end Polysaccharides – Structure Cellulose b-(1-4) linkage 180 deg rotation 300- 15,000 Glc residues Rigid extended conformation H-bonding Forms bundles or fibrils Plant cell walls, stems and branches Humans don’t have b-glucosidases Microbe that live in ruminants do termites Amylose Polysaccharides – Structure • Chitin 2nd most abundant organic compound on earth – found in exoskeletons of insects and crustaceans, and in cell wall of algae and fungi – composed of β- (1-4)linkage of GlcNAc residues. 180 deg rotation H-bonding Adjacent strands Glycoconjugates: Proteoglycans unbranched • Glycosaminoglycans have dissaccharide components (repeating) heteroglycan – 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 joints Elastic and resistant to compression cartilage cartilage Glycoconjugates: Peptidoglycan Bacteria cell wall, heteroglycans chains linked to peptides GlcNAc linked to N-acetylmuramic acid (MurNAc) joined by β -(1-4) linkage Large/rigid mol Defines shape of cell Gram stain +/- Glycoconjugates - Glycoproteins • 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 Glycoconjugates - Glycoproteins N-linked Large amt of structural diversity possible !! Glycoconjugates Glycoproteins 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 b-D-ribofuranosyl –(1-4)-a-D-glucopyranose. Is this a reducing or nonreducing sugar? • Compare and contrast the structures of starch, glycogen and cellulose.