DANEVA REYES DANEVA REYES DANEVA REYES DANEVA REYES DANEVA REYES DANEVA REYES DANEVA REYES DANEVA REYES Carbohydrates or Saccharides - constitute one of three important nutrient biomolecules (the others are proteins and lipids) - considered to be the most widespread biomolecules in living organisms - described as polyhydroxyl (or polyhydric) carbonyl compounds- aldehydes (Aldoses) + ketones (Ketoses) including their derivatives and condensation products - composed of predominantly C,H and O - other elements may be present like N, S, P (derived carbohydrates)Simple Carbohydrates: CHO w/alcohol; aldoses and ketoses; formyl group, free aldehyde group; ketonic groupComplex Carbohydrates: with other functional groups; contain other chemicals (ex. Derived carbohydrate)ClassificationsA. Based on Hydrolyzability1. Monosaccharides: simple sugars, cannot be hydrolyzed further Traditional chemical name of carbohydrates carry the suffix: -OSE Carbohydrates, generally are polyfunctional with Aldehyde or formyl group: terminal Ketonic group: Internal Alcoholic groups: Primary (terminal); Secondary (internal) Other groups: Amino group: -NH2 Carboxyl group: -COOH Classified further based on principal functional group present Aldoses With free aldehyde group or formyl group Name: -----ose Ketoses With ketonic group Name (in some cases): -----ulose Monosaccharides with CHO only may conform with empirical formula as hydrated carbon (CH2O)n for aldoses and ketoses Classified further based on the number of C-atoms Triose: 3 C atoms Tetriose: 4 C atoms Pentose: 5 C atoms Hexose: 6 C atoms Derived monosaccharides: contain other functional groups Sugar acids (products of REDOX) Sugar alcohols (products of REDOX) Sugar amines Sugar phosphates O glycosides Heterocyclic hemiacetals and hemiketals2. Oligosaccharides: hydrolyzed completely to produce 2 10 monosaccharides Examples: Disaccharides: Sucrose Maltose Isomaltose Lactose Cellubiose Trisaccharides Tetrasaccharides, etc. Note: The term sugar applies to certain water-soluble monosaccharides and disaccharides that have a sweet taste. The sweet taste has been associated usually but not necessarily with the OH group. The sweetest carbohydrate is fructose3. Polysaccharides: hydrolyzed completely to produce 10 or more monosaccharides Glycan linked by glycosidic bond Classified based on the number of C-atoms in the monosaccharide unit released Pentosan: releases 5C monosaccharide unit Hexosan: releases 6-C monosaccharide unit Classified further based on the type of monosaccharide unit released Glucan or glucosan: releases glucose Fructosan: releases fructose Classified further based on the number of type of monosaccharide unit released Homopolysaccharide: composed of one type of monosaccharide unit Example: Starch (Glucose) Glycogen (Glucose) Chitin (N-acetylglucosamine) Heteropolysaccharide: composed of more than one type of monosaccharide unit released Example: Galactomannan: galactose & manose Hyaluronic acid: Beta-glucuronic acid & N-acetylglucosamine Heparin: sulfated glucosamine & sulfated iduronic acid Classified based on the nature of monosaccharide unit released Simple polysaccharide Complex polysaccharide Consists of monosaccharide derivativesDietary Fiber: consists of nondigestible carbohydrates including cellulose, lignin and pectin provides no energy but has beneficial effects in the diet:1. Adds bulk to the diet (roughage); absorbes 10 15x its own weight in water, drawing liquid into the lumen of the intestine and increasing bowel motility by softening fecal matter.2. Binding property decreases absorption of toxic substances including certain carcinogens3. Decreases risk for constipation, hemorrhoids, diverticulosis and colon cancerNegative Effects of Excessive fiber:1. Can bind trace elements (ex. Zn+2)2. Decrease the absorption of fat-soluble vitamins: A,D,E,K 20 35 g/day from whole grain cereals, bread, fruits, vegetables and legumes.Because of its fibrous nature, it encourages chewing or mastication which in turn induces secretions of certain hormones that can improve digestion, such as gastrin and cholecystokinin. Without these hormones, it takes longer to reach the feeling of satiety.B. Based on Function1. Reserve or Storage or Nutrient carbohydrate Metabolized as a source of energy Energy obtained is transported to the mitochondrion in the form of reducing equivalents such as NAD + FAD. These compounds are oxidized along the ETC in the inner membrane of the mitochondrion and the energy released is used to synthesize high energy phosphate compounds such as ATP OXIDATIVE PHOSPHORYLATION Oxidative degradation CO2 + H2O Example: Animal: Glycogen Plant: Starch2. Structural carbohydrates: for support or protection Examples: Chitin: in the exoskeleton of insects and crustaceans Cellulose: fibrous framework of plants3. Biologically active carbohydrates: associated with other functions Metabolites in different metabolic pathway Ex. Sugar phosphates In conjugation with other biomolecules Examples: Glycoproteins: catalytic & regulatory Carbohydrate increases water solubility of the conjugated biomoleculeCarbohydrates: Structure (Nomenclature & Isomerism) Configuration on the penultimate c-atom: L and D Penultinate Carbon atom: asymmetric or chiral C-atom; farthest removed from the functional group and which is assigned the highest location number In hexose: C5 In Pentose: C4 Assymetric or chiral C-atom: tetragonal; single bonded; covalently binded to four different atoms or groupsD-aldosesD-GlyceraldehydeNatural configurationCarries D-configuration on the penultimate carbon atom

Condensed Kekule StructurePenultimate; Asymmetric C-atom: 2Fischer Projection Formula

Ball and Stick Formula

L-Glyceraldehyde

D-aldosesTriose:

Tetrose:

Pentose:

Hexose:

D-Ketoses NO ASYMMETRIC CARBON

C# 3. Asymmetric carbon

Nomenclature --OSE: traditional suffix; indicates an aldose --ULOSE: traditional suffix; indicates a ketose Exceptions: Fructose (gluculose) Psicose Sorbose TagatoseIsomerism Stereoisomers: isomers (same molecular formula); with the same structure but differ in conformation or configuration Conformational stereoisomers: Stereocenter restricted rotation about C-C single bond 4C, chair, puckered and envelope Configurational stereoisomers: Stereoisomers that differ in spatial arrangement of atom or groups about a stereocenter Chiral or Asymmetric C-atom in carbohydrates imparts the ability to exhibit configurational stereoisomerism Vant Hoff states that if a molecule has n different asymmetric c-atom, it may exists in 2n stereoisomer forms 2n no. of stereoisomers It also allows the carbohydrate to exhibit optical activity Dextrorotatory: d or (+) Levorotatory: l or (-) Optical Isomers Optical activity & Configuration (D or L) are not related to each otherConfigurational stereoisomers in carbohydrates: asymmetric or chiral C-atoms (stereocenter in carbohydrates) Enantiomers: non-superimposable mirror image stereoisomers; differ in optical activity Example D+L configurations of isomeric monosaccharides D + L glucose Vant Hoff rule: 2n = no. of stereoisomers No. of stereoisomers divided by 2 = no. of pairs of enantiomers Equimolar mixture of D + L enantiomers is not optically active due to external compensation Molecules of the enantiomers will mutually and equally cancel out each others optical activity Diastereomers: non-superimposable non-mirror image stereoisomers Organic compounds with one C-atom cannot exhibit diastereomerism Organic compounds with more than one c-atom can Examples: D-ribose D-arabinose Epimers: diastereomers that differ in configuration on one asymmetric C-atom and have the same configuration on other asymmetric C-atom Examples: 2-Epimers Differ in configuration on C2 Same configuration on C3 & C4 Anomers: diastereomers that differ in configuration on the anomeric C-atom (C1 for aldoses; C2 for Ketoses) Designated as either -anomer or -anomer

Free anomeric C-atom Imparts reducing properties Able to mutarotate Mutarotation: acyclic cyclic Water, neutral = -anomer Water, H+ = -anomerStructure of Glucose Emil Fischer: received nobel prize in chemistry for his studies on the structure of glucose and for establishing the configuration of the 4-asymmetric C-atoms in the aldohexose Glucose in solid form is quite inert to oxygen When dissolved in water or acetic acid, glucose undergoes mutarotation forming an anomer. The anomer crystallizes out where the solvent is evaporated completely Mutarotation is reversible and takes place if the anomeric C-atom is free. It is the free anomeric C-atom that imparts the reducing property to the carbohydrate The monosaccharide cyclicizes in the solution -anomer most stableNOTE: In a D-glucose solution (aq.), an equilibrium mixture consists of three forms of the sugar: approximately 33% - -anomer; 66% - -anomer; 1% acyclic form. BUT however, in a biological septum the -anomer is favored at physiological pH

HAWORTH STRUCTURES:

Pyranose rings exists preferably in chair conformations.The natural conformation is a 4C, chair conformation; torsional strain, bulk or Van der Waals strain + Baeyers strain are all minimized

Furanose rings exists preferably in envelope or puckered conmformation.Axial and Equatorial positions are not prominent: Quasi-axial & Quasi-equatorial

WN. Haworth, English Chemist, explained the existence of 2 forms of glucose and showed that aldohexose and other sugars react internally to form a heterocyclic hemiacetal. A hemiacetal is formed between an aldehyde & an alcohol in an Nucleophilic Addition reaction. A hemiketal is formed between a ketone and an alcohol via the same reaction.

A 6-membered or 5-membered ring is favored because they allow conversion to relaxed and stable conformations. 6-membered rings become a carbohydrate derivative of pyran5-membered rings become a carbohydrate derivative of furanThe rings are more stable if the big atoms in groups are accommodated at the equatorial position.

Additional:Forms of Structural Isomerism in Carbohydrates: Functional isomers: differ in functional groups Ex. Glucose (aldose) + Fructose (ketose) Skeletal isomers: differ in parent carbon chain Ex. -D(-)-fructopyranose A-D(-)-fructofuranoseDerivatives of Monosaccharides Products of REDOX Sugar acids: products of oxidation

Lactone: cyclic carboxylic acid ester; product of oxidation; Tollens test

Sugar Alcohols: products of reduction

Deoxysugars: products of reduction Example: L-furose (L-6-deoxygalactose) B-D-2-deoxyribose (B-D-2-deoxyribofuranose) in DNA Sugar Phosphates: phosphate ester Example: B-D-glucose + ATP ADP + B-D-glucose-6-phosphate

O-glycosides: full acetals; furanosides + pyranosides Example Methyl--D-glucopyranoside

Sugar amines or Amino sugars Example: N-acetyl--D-glucosamine N-acetyl muramic acid

DisaccharidesDistinguishing features:1. Monosaccharide units and corresponding stereoconfiguration2. Glycosidic bonds: not an ether linkage because it can be hydrolyze3. Order of the 2 monosaccharide units if they are different4. Anomeric configuration: C1 for aldoses, C2 for ketosesSucrose: Perhaps the most important disaccharide Energy source in all photosynthetic plants Table sugar; Cane sugar; comes from sugar cane; also present in sugar beets White crystalline solid Non-reducing Cannot mutarotate in solution. The anomeric C-atom of the monosaccharide units are in glycosidic linkage GluC1C2Fru

Hydrolysis of sucrose catalyzed by invertase invert sugars Invert sugars: equimolar mixtures of D-glucose and D-fructose. Involves inversion, accompanied by a net change in optical activity from d to l forming a racemic mixture containing invert sugars (not optically active): Glucose (+) d + Fructose (-) l

Lactose: Milk sugar, found in human milk (25%) Can mutarotate in solution Has a reducing end (Free anomeric C-atom)

Maltose: Malt sugar Starch (diastase)maltose(maltase)glucose Has reducing end, can mutarotate in solution Disaccharide unit of starch and glycogen

Isomaltose: Disaccharide unit of limit dextrin Has reducing end and can mutarotate

Cellubiose: Disaccharide unit of cellulose Has reducing end and can mutarotate

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