(4) 단당류의 유도체 * 우론산 - 그림 7.24, 간에서 글루쿠론산은 스테로이드, 약물, 빌리루빈, 헤모글로빈 등과 결합하여 수용성증가 * 아미노당 - 당의 두번째 탄소의 히드록시기가 아미노기로 치환 ( 그림 7.25) * 디옥시당 --OH 기가 –H 로 대체된 단당류 ( 그림 7.26) 7.2 이당류 - 다양한 유형의 글리코시드결합 ( 그림 7.27) - 락토오스 비내성 * 락토오스 - 갈락토오스, 글루코오스의 β- 글리코시드결합 ( 그림 7.28) * 말토오스 - 그림 7.29 * 셀로비오스 -β(1,4) 글리코시드결합 ( 그림 7.230) * 수크로오스 ( 설탕 ) -α- 글루코오스와 β- 프룩토오스로 구성 ( 그림 7.31), 비환원당

Section 7.1: Monosaccharides  Important Monosaccharides  Glucose ( D -Glucose) — originally called dextrose, it is found in large quantities throughout the natural world  The primary fuel for living cells  Preferred energy source for brain cells and cells without mitochondria (erythrocytes) Figure 7.21  - D -glucopyranose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.1: Monosaccharides  Fructose ( D -Fructose) is often referred to as fruit sugar, because of its high content in fruit  On a per - gram basis, it is twice as sweet as sucrose; therefore, it is often used as a sweetening agent in processed food  Sperm use fructose as an energy source Figure 7.22  -D-fructofuranose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.1: Monosaccharides  Galactose is necessary to synthesize a variety of important biomolecules  Important biomolecules include lactose, glycolipids, phospholipids, proetoglycan, and glycoproteins  Galactosemia is a genetic disorder resulting from a missing enzyme in galactose metabolism Figure 7.23  -D-galactopyranose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.1: Monosaccharides  Monosaccharide Derivatives  Uronic Acids —  - D -glucuronate (7.24a) and its epimer  - L -iduronate (7.24b) are important in animals  D -Glucuronic acid is used in the liver to improve water solubility to remove waste molecules Figure 7.24 Uronic Acids From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.1: Monosaccharides  Monosaccharide Derivatives Continued  Amino Sugars — in amino sugars, a hydroxyl group (usually on carbon 2) is replaced with an amine group  D -Glucosamine (a) and D - galactosamine (b) are the most common and often attached to proteins or lipids Figure 7.25 Amino Sugars From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.1: Monosaccharides  Monosaccharide Derivatives Continued  Deoxy Sugars — Monosaccharides that have an –OH replaced by an –H or –CH 3  2-deoxy- D -ribose (7.25b) is the pentose sugar of DNA and fucose (7.25a) is part of ABO blood group determinants Figure 7.26 Deoxy Sugars From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.2: Disaccharides  Disaccharides  Two monosaccharides linked by a glycosidic bond  Linkages are named by  - or  -conformation and by which carbons are connected (e.g.,  (1,4) or  (1,4)) Figure 7.27 Glycosidic Bonds From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.2: Disaccharides  Disaccharides Continued  Lactose (milk sugar) is the disaccharide found in milk  One molecule of galactose linked to one molecule of glucose (  (1,4) linkage)  It is common to have a deficiency in the enzyme that breaks down lactose (lactase)  Lactose is a reducing sugar Figure 7.28  - and  -lactose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.2: Disaccharides  Disaccharides Continued  Maltose (malt sugar) is an intermediate product of starch hydrolysis   (1,4) linkage between two molecules of glucose  Does not exist freely in nature Figure 7.29  - and  -Maltose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.2: Disaccharides  Disaccharides Continued  Cellobiose is a degradation product of cellulose  Cellobiose is composed of two molecules of glucose linked with a  (1,4) glycosidic bond  Does not exist freely in nature Figure 7.30  -Cellobiose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.2: Disaccharides  Disaccharides Continued  Sucrose is common table sugar (cane or beet sugar) produced in the leaves and stems of plants  One molecule of glucose linked to one molecule of fructose, linked by an ,  (1,2) glycosidic bond  Glycosidic bond occurs between both anomeric carbons  Sucrose is a nonreducing sugar Figure 7.31 Sucrose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

7.3 다당류 * 올리고당류 : N-, O- 연결 올리고당류 ( 그림 7.32) (1) 동질그리칸 * 전분 - 아밀로오스 ( 그림 7.33): α(1,4) 글리코시드결합 - 아밀로펙틴 ( 그림 7.34a): α(1,4), α(1,6) 의 가지사슬의 중합체 * 글리코겐 - 아밀로펙틴과 유사 ( 그림 7.34b) * 셀룰로오스 -β(1,4) 글리코시드결합 ( 그림 7.35) - 미세원섬유 ( 그림 7.36) * 키틴 : N- 아세틸글루코사민의 β(1,4) 글리코시드결합 ( 그림 )

Section 7.3: Polysaccharides  Polysaccharides (glycans) are composed of large numbers of monosaccharides connected by glycosidic linkages  Smaller glycans made of 10 to 15 monomers called oligosaccharides, most often attached to polypeptides as glycoproteins  Two broad classes : N- and O-linked oligosaccharides From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  N-linked oligosaccharides are attached to polypeptides by an N-glycosidic bond with the side chain amide nitrogen from the amino acid asparagine  Three major types of asparagine-linked oligosaccharides: high mannose, hybrid, and complex Figure 7.32 Oligosaccharides Linked to Polypeptides From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  O-Glycosidic linkages attach glycans to the side chain hydroxyl of serine or threonine residues or the hydroxyl oxygens of membrane lipids Figure 7.32 Oligosaccharides Linked to Polypeptides From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Larger glycans may be hundreds or thousands of subunits  Polysaccharides can be linear or branched  Polysaccharides have been divided into two classes: homoglycans and heteroglycans From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Homoglycans  Have one type of monosaccharide and are found in starch, glycogen, cellulose, and chitin (glucose monomer)  Starch and glycogen are energy storage molecules while chitin and cellulose are structural From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Homoglycans  Chitin is part of the cell wall of fungi and arthropod exoskeleton  Cellulose is the primary component of plant cell walls  No fixed molecular weight, because the size is a reflection of the metabolic state of the cell producing them From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Starch — the energy reservoir of plant cells and a significant source of carbohydrate in the human diet  Two polysaccharides occur together in starch: amylose and amylopectin  Amylose is composed of long, unbranched chains of D - glucose with  (1,4) linkages between them Figure 7.33 Amylose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Amylose typically contains thousands of glucose monomers and a molecular weight from 150,000 to 600,000 Da  The other form is amylopectin, which is a branched polymer containing both  (1,6) and  (1,4) linkages  Branch points occur every 20 to 25 residues Figure 7.33 Amylose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Glycogen is the carbohydrate storage molecule in vertebrates found in greatest abundance in the liver and muscle cells  Up to 8–10% of the wet weight of liver cells and 2–3% in muscle cells  Similar in structure to amylopectin, with more branch points  More compact and easily mobilized than other polysaccharides From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides Figure 7.34 (a) Amylopectin and (b) Glycogen From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Cellulose is a polymer of D -glucopyranosides linked by  (1,4) glycosidic bonds  It is the most important structural polysaccharide of plants (most abundant organic substance on earth) Figure 7.35 The Disaccharide Repeating Unit of Cellulose From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Pairs of unbranched cellulose molecules (12,000 glucose units each) are held together by hydrogen bonding to form sheetlike strips, or microfibrils  Each microfibril bundle is tough and inflexible with a tensile strength comparable to that of steel wire  Important for dietary fiber, wood, paper, and textiles Figure 7.36 Cellulose Microfibrils From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

(2) 이질다당류 *N- 및 O- 글리칸 * 글리코사미노글리칸 (GAG) - 이당류반복단위 ( 그림 7.37) 를 갖는 선형중합체로 당 잔기의 대부분이 아미노유도체임 - 황산염기, 카르복실기를 갖음 - 생리적 pH 에서 음전하, 다량의 물을 흡수 (1000 배이상 : 히알우론산 ) (* 뮤레인 - 펩티도글리칸으로도 불림 ( 그림 ) - 펩티드교차다리 ( 그림 )) 7.4 당접합체 - 탄수화물이 단백질, 지질과 공유결합으로 연결된 화합물 (1) 프로테오글리칸 - 건량의 95% 가 탄수화물, 조직의 세포외기질 - 핵심단백질에 GAG 가 N- 와 O- 글리코시드결합으로 연결 ( 그림 7.38) - 다음이온 : 조직의 지지와 탄력성제공, 예로 연골 - 다세포조직에 지지와 세기 제공 ( 콜라겐, 라미닌 피브로넥틴과 함께 ) - 뮤코다당체침착증 ( 과도한 축척 ), 후를러증후군 ( 더마틴 황산염축적 )

Section 7.3: Polysaccharides  Heteroglycans  High-molecular-weight carbohydrate polymers that contain more than one type of monosaccharide  Major types: N- and O-linked glycosaminoglycans (glycans), glycosaminoglycans, glycan components of glycolipids, and GPI (glycosylphosphatidylinositol) anchors  GPI anchors and glycolipids will be discussed in Chapter 11 From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Heteroglycans Continued  N- and O-Glycans — many proteins have N- and O- linked oligosacchaarides  N-linked (N-glycans) are linked via a  -glycosidic bond  O-linked (O-glycans) have a disaccharide core of galactosyl-  -(1,3)-N-acetylgalactosamine linked via an  -glycosidic bond to the hydroxyl of serine or threonine residues From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides  Heteroglycans Continued  Glycosaminoglycans (GAGs) are linear polymers with disaccharide repeating units  Five classes: hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin and heparin sulfate, and keratin sulfate  Varying uses based on repeating unit From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.3: Polysaccharides Figure 7.37 Glycosamino Glycan Structures From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.4: Glycoconjugates  Glycoconjugates result from carbohydrates being linked to proteins and lipids  Proteoglycans  Distinguished from other glycoproteins by their high carbohydrate content (about 95%)  Occur on cell surfaces or are secreted to the extracellular matrix Figure 7.38 Proteoglycan Aggregate From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.4: Glycoconjugates  Proteoglycans Continued  All proteoglycans contain GAG chains that are linked to core proteins by N- and O-glycosidic bonds  Aggrecan is an example of a type of proteoglycan that is found in abundance in cartilage  It is a core protein linked to over 100 chondroitin sulfate and 40 keratin sulfate chains  Up to 100 aggrecans are in turn attached to hyaluronic acid to form a proteoglycan aggregate From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.4: Glycoconjugates  Proteoglycans Continued  Have roles in organizing extracellular matrix and are involved in signal transduction  Metabolism of proteoglycans involved in many genetic disorders, including Hurler’s syndrome Figure 7.38 Proteoglycan Aggregate From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

(2) 당단백질 -O- 연결 ( 세린, 트레오닌의 –OH 와 연결 ) 혹은 N- 연결 ( 탄수화물이 1-85%) * 아스파라긴 - 연결 탄수화물 (N- 글리코시드결합 ) - 만노오스타입, 복합타입, 혼성타입 ( 그림 ) * 뮤신 - 타입 탄수화물 - 부동액 당단백질 등 다양 ( 그림 ) * 당단백질의 기능 - 표 7.1: 트랜스페린, 혈액응고인자, 보체 등 - 세포생물의 인식과정, 변성의 방지, 점성의 증가, 얼음결정의 성장을 지연 등 - 당질피질 ( 글리코칼릭스 ) 는 세포부착에 중요 ( 그림 7.39) 7.5 당암호 - 세포정보전이 : 주화성은 세포막 수용체에 의해 감지, 거대한 분자코드가 필요 * 렉틴 : 당암호의 번역자 - 당코드의 해독은 렉틴에 의해 : 탄수화물결합단백질 - 세포간 상호작용에 필요 ( 그림 7.40) -Helicobacter pylori 는 위점막을 감염시키는 여러 렉틴을 갖음 - 콜레라독소의 창자표면의 당지질에 결합 - 백혈구구르기는 렉틴결합에 의해 일어남 * 복합당질 : 당사슬, 미세유전성이질성

Section 7.4: Glycoconjugates  Glycoproteins  Commonly defined as proteins that are covalently linked to carbohydrates through N- and O-linkages  Several addition reactions in the lumen of the endoplasmic reticulum and Golgi complex are responsible for final N-linked oligosaccharide structure  O-glycan synthesis occurs later, probably initiating in the Golgi complex  Carbohydrate could be 1%–85% of total weight From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.4: Glycoconjugates  Glycoprotein Functions occur in cells as soluble and membrane-bound forms and are nearly ubiquitous in living organisms  Vertebrate animals are particularly rich in glycoproteins From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.4: Glycoconjugates  Functions of glycoproteins include enzymes, blood clotting, hormone, receptor proteins, transport proteins, and cell adhesion From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.4: Glycoconjugates Figure 7.39 The Glycocalyx From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.5: The Sugar Code  Living organisms require large coding capacities for information transfer  Profound complexity of functioning systems  To succeed as a coding mechanism, a class of molecules must have a large capacity for variation  Glycosylation is the most important posttranslational modification in terms of coding capacity  More possibilities with hexasaccharides than hexapeptides From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.5: The Sugar Code  In addition to their immense combinatorial possibilities they are also relatively inflexible, which makes them perfect for precise ligand binding  Lectins  Lectins, or carbohydrate-binding proteins, are involved in translating the sugar code  Bind specifically to carbohydrates via hydrogen bonding, van der Waals forces, and hydrophobic interactions From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press

Section 7.5: The Sugar Code Figure 7.40 Role of Oligosaccharides in Biological Recognition  Lectins Continued  Biological processes include binding to microorganisms, binding to toxins, and involved in leukocyte rolling From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press