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(4)단당류의 유도체
*우론산
-그림7.24, 간에서 글루쿠론산은 스테로이드, 약물, 빌리루빈, 헤모글로빈 등과
결합하여 수용성증가
*아미노당
-당의 두번째 탄소의 히드록시기가 아미노기로 치환(그림 7.25)
*디옥시당
--OH기가 –H로 대체된 단당류(그림7.26)
7.2 이당류
-다양한 유형의 글리코시드결합(그림7.27)
-락토오스 비내성
*락토오스
-갈락토오스, 글루코오스의 β-글리코시드결합(그림7.28)
*말토오스
-그림7.29
*셀로비오스
-β(1,4)글리코시드결합(그림7.230)
*수크로오스(설탕)
-α-글루코오스와 β-프룩토오스로 구성(그림7.31), 비환원당
Section 7.1: Monosaccharides
Figure 7.21 a-D-glucopyranose
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)
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press
Section 7.1: Monosaccharides
Figure 7.22 b-D-fructofuranose
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
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press
Section 7.1: Monosaccharides
Figure 7.23 a-D-galactopyranose
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
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press
Section 7.1: Monosaccharides
Monosaccharide Derivatives
Uronic Acids—a-D-glucuronate (7.24a)
and its epimer b-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
Figure 7.25 Amino Sugars
sugars, a hydroxyl group
(usually on carbon 2) is
replaced with an amine group
D-Glucosamine (a) and Dgalactosamine (b) are the
most common and often
attached to proteins or
lipids
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
–CH3
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
Figure 7.27 Glycosidic Bonds
Disaccharides
Two monosaccharides linked by a glycosidic bond
Linkages are named by a- or b-conformation and by
which carbons are connected (e.g., a(1,4) or b(1,4))
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 (b(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 a- and b-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
a(1,4) linkage between two
molecules of glucose
Does not exist freely in nature
Figure 7.29 a- and b-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
Figure 7.30 b-Cellobiose
Cellobiose is composed of two
molecules of glucose linked with
a b(1,4) glycosidic bond
Does not exist freely in nature
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 a,b(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(그림7.32)
(1)동질그리칸
*전분
-아밀로오스(그림7.33): α(1,4)글리코시드결합
-아밀로펙틴(그림7.34a): α(1,4), α(1,6)의 가지사슬의 중합체
*글리코겐
-아밀로펙틴과 유사(그림7.34b)
*셀룰로오스
-β(1,4)글리코시드결합(그림7.35)
-미세원섬유(그림7.36)
*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
Figure 7.32 Oligosaccharides
Linked to Polypeptides
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
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press
Section 7.3: Polysaccharides
Figure 7.32 Oligosaccharides
Linked to Polypeptides
O-Glycosidic linkages attach glycans to the side chain
hydroxyl of serine or threonine residues or the hydroxyl
oxygens of membrane lipids
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
Figure 7.33 Amylose
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 Dglucose with a(1,4) linkages between them
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press
Section 7.3: Polysaccharides
Figure 7.33 Amylose
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 a(1,6) and a(1,4) linkages
Branch points occur every 20 to 25 residues
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
Figure 7.35 The
Disaccharide Repeating
Unit of Cellulose
Cellulose is a polymer of D-glucopyranosides linked
by b(1,4) glycosidic bonds
It is the most important structural polysaccharide of
plants (most abundant organic substance on earth)
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press
Section 7.3: Polysaccharides
Figure 7.36 Cellulose
Microfibrils
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
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press
(2)이질다당류
*N-및 O-글리칸
*글리코사미노글리칸(GAG)
-이당류반복단위(그림7.37)를 갖는 선형중합체로 당 잔기의 대부분이
아미노유도체임
-황산염기, 카르복실기를 갖음
-생리적 pH에서 음전하, 다량의 물을 흡수(1000배이상: 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 GAG가 N- 와 O-글리코시드결합으로 연결(그림7.38)
-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 Olinked oligosacchaarides
N-linked (N-glycans) are linked via a b-glycosidic bond
O-linked (O-glycans) have a disaccharide core of
galactosyl-b-(1,3)-N-acetylgalactosamine linked via an
a-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 –OH와 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
-표7.1: 트랜스페린, 혈액응고인자, 보체 등
- 세포생물의 인식과정, 변성의 방지, 점성의 증가, 얼음결정의 성장을 지연 등
-당질피질(글리코칼릭스)는 세포부착에 중요(그림7.39)
7.5 당암호
-세포정보전이: 주화성은 세포막 수용체에 의해 감지, 거대한 분자코드가 필요
*렉틴: 당암호의 번역자
-당코드의 해독은 렉틴에 의해: 탄수화물결합단백질
- 세포간 상호작용에 필요(그림7.40)
-Helicobacter pylori는 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
Lectins Continued
Biological processes
include binding to
microorganisms,
binding to toxins, and
involved in leukocyte
rolling
Figure 7.40 Role of Oligosaccharides in
Biological Recognition
From McKee and McKee, Biochemistry, International Fifth Edition, © 2012 by Oxford University Press