7.1 단당류 -알토오스(알데히드기), 케토오스(케톤기)(그림7.1) -가장 간단한 알토오스 케토오스(그림7.2) -글루코오스: 알도헥소오스 (1)단당류의 입체이성질체 -광학적으로 활성있는 물질에서 비대칭단소를 키랄탄소 -자연적으로 생기는 당 은 D-구조, D-알도오스 계보(그림7.3) -거울상이성질체가 아닌 입체이성질체를 부분이성질체라 함 알도펜토오스인 D-리보오스와 L-리보오스는 D-아라비노오스와 L-아라비노오스 의 거울상이성질체(그림7.4). 하나의 비대칭 탄소원자에서 구조가 다른 부분이성질체를 에피머라함

Chapter 7 Carbohydrates Overview Section 7.1: Monosaccharides Section 7.2: Disaccharides Section 7.3: Polysaccharides Section 7.4: Glycoconjugates Section 7.5: The Sugar Code From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Carbohydrates are the most abundant biomolecule in nature Chapter 7: Overview Carbohydrates are the most abundant biomolecule in nature Have a wide variety of cellular functions: energy, structure, communication, and precursors for other biomolecules They are a direct link between solar energy and chemical bond energy From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.1 General Formulas for the Aldose and Ketose Forms of Monosaccharides Monosaccharides, or simple sugars, are polyhydroxy aldehydes or ketones Sugars with an aldehyde functional group are aldoses Sugars with an ketone functional group are ketoses From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.2 Glyceraldehyde (an Aldotriose) and Dihydroxyacetone (a Ketotriose) Carbohydrates are also classified by the number of carbon atoms they contain Trioses, tetroses, pentoses, and hexoses Most abundent in living cells are hexoses and pentoses Class names often combine information about carbon number and functional group From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Monosaccharide Stereoisomers An increase in the number of chiral carbons increases the number of possible optical isomers 2n where n is the number of chiral carbons Figure 7.3 The D Family of Aldoses From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Almost all naturally occurring monosaccharides are the D form All can be considered to be derived from D-glyceraldehyde or nonchiral dihydroxyacetone Figure 7.3 The D Family of Aldoses From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides In optical isomers, the reference carbon is the asymmetric carbon farthest from the carbonyl carbon Diastereomers are stereoisomers that are not enantiomers (mirror-image isomers) (i.e., D-ribose and D-arabinose) Figure 7.4 The Optical Isomers D- and L- Ribose and D- and L- Arabinose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Diastereomers that differ at a single chiral carbon are epimers (e.g., D-glucose and D-galactose) From Figure 7.3 From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

(2) 단당류의 고리구조 -4개 또는 그 이상의 탄소를 갖는 당은 주로 고리구조를 형성: 알데히드와 케톤기가 당의 히드록시기와 반응하여 고리모양의 헤미아세탈 과 헤미케탈을 형성(그림7.5) -카르보닐탄소가 새로운 키랄중심: 이 탄소를 아노머탄소, 이 화합물을 아노머라함: 알도스에서 1번 탄소의 아래에 히드록시기가 있으면 α-아노머(그림7.6) Haworth 구조 -정확한 결합각도와 결합길이를 나타냄(그림7.7) -5개 구성원으로 된 헤미아세탈구조인 푸란은 푸라노오스라 함(그림7.8) 6개 구성원, 피라노오스; 글루코피라노오스 형태구조 -결합각분석과 X-선분석에 의한 형태식(그림7.10) *변광회전 - 단당류의 α-와 β-형은 물에 용해될 때 쉽게 상호전환(그림7.11)

Section 7.1: Monosaccharides Figure 7.5 Formation of Hemiacetals and Hemiketals Cyclic Structure of Monosaccharides Sugars with four or more carbons exist primarily in cyclic forms Ring formation occurs because aldehyde and ketone groups react reversibly with hydroxyl groups in an aqueous solution to form hemiacetals and hemiketals From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.6 Monosaccharide Structure The two possible diastereomers that form because of cyclization are called anomers Hydroxyl group on hemiacetal occurs on carbon 1 and can be in the up position (above ring) or down position (below ring) In the D-sugar form, because the anomeric carbon is chiral, two stereoisomers of the aldose can form the a-anomer or b-anomer From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.7 Haworth Structures of the Anomers of D-Glucose Haworth Structures—these structures more accurately depict bond angle and length in ring structures than the original Fischer structures In the D-sugar form, when the anomer hydroxyl is up it gives a b-anomeric form (left in Fischer projection) while down gives the a-anomeric form (right) From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.8 Furan and Pyran Five-membered rings are called furanoses and six-membered rings are pyranoses Cyclic form of fructose is fructofuranose, while glucose in the pyranose form is glucopyranose Figure 7.9 Fischer and Haworth Representations of D-Fructose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Conformational Structures Conformational structures show the puckered nature of sugar rings X-ray and bond angle analysis Space-filling models also give useful information Figure 7.10 a- and b- D-glucose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Mutarotation The a- and b-forms of monosaccharides are readily interconverted in aqueous environments This spontaneous process, mutarotation, produces an equilibrium mixture of a- and b-forms in both furanose and pyranos ring structures Open chain form can participate in redox reactions Figure 7.11 Equilibrium Mixture of D-Glucose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

*산화환원반응 -단당류의 알데히드기의 산화로 알돈산, CH2OH의 산화로 우론산, 두 부분 모두 산화는 알다린산(그림7.12) -락톤: 알돈산과 우론산의 카르보닐기와 OH기와의 반응(그림) -환원당: 베네딕트시약같은 산화제에 의해 산화되는 당(그림7.13) *환원반응 -알데히드기와 케톤기의 환원은 알디톨형성: D-글루시톨(소비톨)은 습기의 손실을 막음(그림7.14) *이성질화반응 -D-글루코오스의 알칼리용액은 D-만노오스와 D-프룩토오스로 이성질화; 이중결합의 재배치, 중간물질을 엔디올, 상호전환을 에피머화(그림7.15) *에스테르화 -탄수화물의 자유히드록시기는 산과 반응하여 에스테르로 전환(그림7.16)

Section 7.1: Monosaccharides Reaction of Monosaccharides The carbonyl and hydroxyl groups can undergo several chemical reactions Most important include oxidation, reduction, isomerization, esterification, glycoside formation, and glycosylation reactions From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Oxidation—monosaccharides may readily undergo several oxidation reactions in the presence of metal ions or certain enzymes Figure 7.12 Oxidation Products of Glucose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Oxidation of the aldehyde group yields aldonic acid Oxidation of the terminal CH2OH group yields uronic acid Oxidation of both groups yields aldaric acid From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.13 Structure of Ascorbic Acid A lactone can be produced if the carbonyl groups of aldonic or uronic acids react with an OH group in the same molecule Lactones are readily produced in nature, for example, L-ascorbic acid (vitamin C) Vitamin C is a powerful reducing agent that protects cells from reactive oxygen and nitrogen species From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.14 Reaction of Glucose with Benedict’s Reagent Sugars that can be reduced by weak, oxidizing agents such as Benedict’s reagent are called reducing sugars Needs open chain so all aldoses are reducing sugars and ketoses such as fructose are reducing sugars also, due to isomerization From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.15 Structure of D-Glucitol (Sorbitol) Reduction—Sugar alcohols (alditols) are produced by the reduction of aldehyde and ketone groups of monosaccharides Sugar alcohols are used in commercial food processing and in pharmaceuticals (e.g., sorbitol can be used to prevent moisture loss) From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.16 Isomerization of D-Glucose to Form D-Mannose and D-Fructose Isomerization—monosaccharides can undergo several types of isomerization D-glucose incubated in an alkaline solution for several hours produces two isomers: D-mannose and D-fructose Both involve an enediol intermediate From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides The transformation of glucose to fructose is an aldose-ketose interconversion The transformation of glucose to mannose is referred to as epimerization Figure 7.16 Isomerization of D-Glucose to Form D-Mannose and D-Fructose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Esterification—free OH groups of carbohydrates can be converted to esters by reactions with acids Esterification often dramatically changes a sugar’s chemical and physical properties Sulfate esters of carbohydrate molecules are found predominantly in the proteoglycan components of connective tissue Participate in forming of salt bridges between carbohydrate chains From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

*글리코시드형성 -헤미아세탈과 헤미케탈은 알코올과 반응하여 아세탈 또는 케탈을 형성(그림7.17): 이 때 생기는(단당류) 결합을 글리코시드결합, 화합물을 글리코시드 -글루코오스와 메탄올과 반응(그림7.18) -한 단당류의 히드록시기와 다른 단당류의 히드록시기의 아세탈결합으로 이당류형성, 다당류도 *글루코실화 반응 -메일라드반응(그림7.20) (3)중요한 단당류 *글루코오스 -덱스트로오스로 불림(그림7.21) *프록토오스(과당) -그림7.22, 설탕보다 두 배 달다. 갈락토오스(젖당) -그림7.23, 섭취 않되면 글루코오스-1-인산에서 합성가능 -선천성 갈락토오스혈증

Section 7.1: Monosaccharides Figure 7.17 Formation of Acetals and Ketals Glycoside Formation—hemiacetals and hemiketals react with alcohols to form the corresponding acetal and ketal When the cyclic hemiacetal or hemiketal form of the monosaccharide reacts with an alcohol, the new linkage is a glycosidic linkage and the compound a glycoside From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.18 Methyl Glucoside Formation Naming of glycosides specifies the sugar component Acetals of glucose and fructose are glucoside and fructoside From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides If an acetal linkage is formed between the hemiacetal hydroxyl of one monosaccharide and the hydroxyl of another, this forms a disaccharide In polysaccharides, large numbers of monosaccharides are linked together through acetal linkages From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Glycosylation Reactions attach sugars or glycans (sugar polymers) to proteins or lipids Catalyzed by glycosyl transferases, glycosidic bonds are formed between anomeric carbons in certain glycans and oxygen or nitrogen of other types of molecules, resulting in N- or O-glycosidic bonds From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Glycation is the reaction of reducing sugars with nucleophilic nitrogen atoms in a nonenzymatic reaction Most researched example of the glycation reaction is the nonenzymatic glycation of protein (Maillard reaction) The Schiff base that forms rearranges to a stable ketoamine, called the Amadori product Can further react to form advanced glycation end products (AGEs) Promote inflammatory processes and involved in age-related diseases From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press

Section 7.1: Monosaccharides Figure 7.20 The Maillard Reaction From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 Oxford University Press