Bioquímica- 1 carbohidratos
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Transcript of Bioquímica- 1 carbohidratos
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Carbohydrates
Copyright 1999-2005 by Joyce J. Diwan.
All rights reserved.
Molecular Biochemistry I
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EL PRINCIPAL CICLO ENERGTICO DE LA BISFERA:Fotosntesis y Respiracin.
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Monosaccharides - simple sugars with multiple OHgroups. Based on number of carbons (3, 4, 5, 6), a
monosaccharide is a triose, tetrose, pentose or hexose.
Disaccharides - 2 monosaccharides covalently linked.
Oligosaccharides - a few monosaccharides covalentlylinked.
Polysaccharides - polymers consisting of chains of
monosaccharide or disaccharide units.
Carbohydrates (glycans) have the followingbasic composition: I
(CH2O)n or H-C-OHI
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CHOs REPRESENTATIVOS: MONO-, DI- Y POLI-SACRIDO(MONMERO, OLIGMERO Y POLMERO)
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Monosaccharides
Aldoses (e.g., glucose) have
an aldehyde group at one
end.
Ketoses (e.g., fructose) have
a keto group, usually at C2.
EL SUFIJO OSA
ALDOSA O CETOSA;TRIOSA, HEXOSA,
ETC- DESIGNACOMPUESTOS COMOLOS SACRIDOS O
AZCARES
C
C OHH
C HHO
C OHH
C OHH
CH2OH
D-glucose
OH
C HHO
C OHH
C OHH
CH2OH
CH2OH
C O
D-fructose
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TRIOSAS, LOS MONOSCARIDOSMS SENCILLOS
INTERCONVERSIN TAUTOMRICA ALDOSA-CETOSA
ENANTIMEROS DELGLICERALDEHIDO
* TAUTMEROS. Ismerosestructurales que difieren en la
distribucin de sus H y =
* ENANTIMEROS:ISMEROS PTICOS
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D vs L Designation
D & L designations are
based on the
configuration aboutthe single asymmetric
C in glyceraldehyde.
The lower
representations are
Fischer Projections.
CHO
C
CH2OH
HO H
CHO
C
CH2OH
H OH
CHO
C
CH2OH
HO H
CHO
C
CH2OH
H OH
L-glyceraldehydeD-glyceraldehyde
L-glyceraldehydeD-glyceraldehyde
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Sugar Nomenclature
For sugars with more
than one chiral center,
D or Lrefers to the
asymmetric C farthest
from the aldehyde or
keto group.Most naturally occurring
sugars are D isomers.
O H O H
C C
H C OH HO C H
HO C H H C OH
H C OH HO C H
H C OH HO C H
CH2OH CH2OH
D-glucose L-glucose
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SISTEMA R-S. Describe la configuracin estereoqumica absolutaPOR CONVENCIN, A CADA GRUPO UNIDO AL C QUIRAL SE LE ASIGNA UNA PIORIDAD:
OR>OH>NH2>COOH>CHO>CH2OH>CH3>H .SI LA PRIORIDAD DE LOS GRUPOS DISTINTOS AL H DISMINUYE EN EL SENTIDO DEL RELOJ,LA CONFIGURACIN ABSOLUTA ES R (LATN RECTUS DER), SI ES AL CONTRARIO, LA
CONFIGURACIN ES S (LATN SINISTERIZQ)
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D & L sugars are mirror
images of one another.
They have the same
name, e.g., D-glucose
& L-glucose.
Other stereoisomers
have unique names,e.g., glucose, mannose,
galactose, etc.
The number of stereoisomers is 2n, where n is the
number of asymmetric centers.The 6-C aldoses have 4 asymmetric centers. Thus
there are 16 stereoisomers (8 D-sugars and 8 L-
sugars).
O H O H
C C
H C OH HO C HHO C H H C OH
H C OH HO C H
H C OH HO C H
CH2OH CH2OH
D-glucose L-glucose
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DIASTERMEROSDE TETROSAS
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PRESENCIA Y FUNCIONES BIOQUMICAS DE LOS MONOSACRIDOS
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Hemiacetal & hemiketal formation
An aldehyde can
react with an
alcohol to form
a hemiacetal.
A ketone can
react with analcohol to form
a hemiketal.
O C
H
R
OH
O C
R
R'
OHC
R
R'
O
aldehyde alcohol hemiacetal
ketone alcohol hemiketal
C
H
R
O R'R' OH
"R OH "R
+
+
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Pentoses and hexoses
can cyclize as the
ketone or aldehyde
reacts with a distalOH.
Glucose forms an
intra-molecular
hemiacetal, as the C1
aldehyde & C5 OHreact, to form a 6-
member pyranose
ring, named after
pyran.Theserepresentations of thecyclic sugars are called
Haworth projections.LOS MONOSACRIDOS DE 5 6 CARBONOS SE ENCUENTRAN PREFERENTEMENTE
EN FORMA DE ESTRUCTURAS CCLICAS DE 5 6 ESLABONES.
H O
OH
H
OHH
OH
CH2OH
H
OH
H HO
OH
H
OHH
OH
CH2OH
H
H
OH
-D-glucose -D-glucose
23
4
5
6
1 1
6
5
4
3 2
H
CHO
C OH
C HHO
C OHH
C OHH
CH2OH
1
5
2
3
4
6
D-glucose
(linear form)
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Fructose forms either
a 6-member pyranose ring, by reaction of the C2 keto
group with the OH on C6, or
a 5-member furanose ring, by reaction of the C2 keto
group with the OH on C5.
CH2OH
C O
C HHO
C OHH
C OHH
CH2OH
HOH2C
OH
CH2OH
H
OH H
H HO
O
1
6
5
4
3
2
6
5
4 3
2
1
D-fructose (linear) -D-fructofuranose
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Cyclization of glucose produces a new asymmetric center
at C1. The 2 stereoisomers are called anomers, & .
Haworth projections represent the cyclic sugars as having
essentially planar rings, with the OH at the anomeric C1:
(OH below the ring) (OH above the ring).
H O
OH
H
OHH
OH
CH2OH
H
-D-glucose
OH
H HO
OH
H
OHH
OH
CH2OH
H
H
OH
-D-glucose
23
4
5
6
1 1
6
5
4
3 2
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Glycosidic Bonds
The anomeric hydroxyl and a hydroxyl of another sugar
or some other compound can join together, splitting outwater to form a glycosidic bond:
R-OH + HO-R' R-O-R' + H2OE.g., methanol reacts with the anomeric OH on glucose
to form methyl glucoside (methyl-glucopyranose).
ENLACES METAESTABLES: DEGRADACIN in vivoSLO MEDIADA POR ENZIMAS
O
H
HO
H
HO
H
OH
OHHH
OH
-D-glucopyranose
O
H
HO
H
HO
H
OCH3
OHHH
OH
methyl--D-glucopyranose
CH3-OH+
methanol
H2O
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Glucsidos. Formacin del enlace glucosdico. No sufren mutarrotacin, lo que ayudaen determinar la configuracin de los azcares. Abundan en tejidos animales yvegetales; algunos son muy txicos (inhiben enzimas que median la utilizacin del
ATP): ouabainaes inhibidor de laATPasa Na+/K+, muy til como herramientafarmacolgica; amigdalina, en semillas de almendras amargasHCN
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Cellobiose, a product of cellulose breakdown, is the
otherwise equivalent anomer (O on C1 points up).
The (14) glycosidic linkage is represented as a zig-zag,
but one glucose is actually flipped over relative to the other.
Disaccharides:Maltose, a cleavage
product of starch
(e.g., amylose), is a
disaccharide with an
(14) glycosidic
link between C1 - C4OH of 2 glucoses.
It is the anomer(C1 O points down).
H O
OH
H
OHH
OH
CH2OH
H
O H
OH
H
OHH
OH
CH2OH
H
O
HH
1
23
5
4
6
1
23
4
5
6
maltose
H O
OH
H
OHH
OH
CH2OH
H
O OH
H
H
OHH
OH
CH2OH
H
H
H
O1
23
4
5
6
1
23
4
5
6
cellobiose
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Polysaccharides
Plants store glucose as amylose or amylopectin, glucose
polymers collectively called starch. Glucose storage in
polymeric form minimizes osmotic effects.
Amylose is a glucose polymer with (14) linkages. Itadopts a helical conformation.
The end of the polysaccharide with an anomeric C1 not
involved in a glycosidic bond is called the reducing end.
H O
OH
H
OHH
OH
CH2OH
HO H
H
OHH
OH
CH2OH
H
O
HH H O
O
H
OHH
OH
CH2OH
HH H O
H
OHH
OH
CH2OH
H
OH
HH O
O
H
OHH
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose
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Glycogen, the glucose storage polymer in animals, is
similar in structure to amylopectin. But glycogen has
more (16) branches.
The highly branched structure permits rapid release of
glucose from glycogen stores, e.g., in muscle during
exercise. The ability to rapidly mobilize glucose is more
essential to animals than to plants.
H O
OH
H
OHH
OH
CH2OH
H
O H
H
OHH
OH
CH2OH
H
O
HH H O
OH
OHH
OH
CH2
HH H O
H
OHH
OH
CH2OH
H
OH
HH O
OH
OHH
OH
CH2OH
H
O
H
O
1 4
6
H O
H
OHH
OH
CH2OH
HH H O
H
OHH
OH
CH2OH
H
H
O
1
OH
3
4
5
2
glycogen
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Cellulose, a major constituent ofplant cell walls, consists
of long linear chains of glucose with (14) linkages.Every other glucose is flipped over, due to the linkages.This promotes intra-chain and inter-chain H-bonds and
van der Waals interactions,
that cause cellulose chains
to be straight & rigid, andpack with a crystalline
arrangement in thick
bundles called microfibrils.
cellulose
H O
OH
H
OHH
OH
CH2OH
H
O
H
OHH
OH
CH2OH
HO
H H O
O H
OHH
OH
CH2OH
H
H O
H
OHH
OH
CH2OH
H
H
OHH O
O H
OHH
OH
CH2OH
HO
H H H H
1
6
5
4
3
1
2
Schematic of arrangement of
cellulose chains in a microfibril.
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These microfibrils arevery strong.The role of cellulose isto impart strength andrigidity to plant cellwalls, which can
withstand highhydrostatic pressuregradients. Osmoticswelling is prevented.
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FUNCIONES NO ESTRUCTURALES DE LOS GLUCOSAMINOGLUCANOS.El cido Hialurnico es un polmero muy soluble en agua; est presente en el lquido sinovial de lasarticulaciones y en el humor vtreo del ojo. Parece actuar incrementando la viscosidad o como agentelubricante en ambos.La Heparina es un anticoagulante natural localizada en muchos tejidos corporales. Une en la sangrea la protena antiprotrombina III y, el complejo resultante, inhibe las enzimas de la cascada de lacoagulacin.
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ANTGENOS DEL GRUPO ABO. Los grupos sanguneosestn determinados por un conjunto de oligosacridosantignicos unidos a la superficie de los eritrocitos.El Tipo O no es antignico pero la persona generaanticuerpos contra los antgenos A y B. Los Tipos A y B se
forman por adicin de GalNac y Gal, respectivamente;ambos pueden generar anticuerpos especficos contra elTipo opuesto (A o B). Los portadores del Tipo AB nogeneran anticuerpos contra ninguno de estos polisacridos.
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Lectins are glycoproteins that recognize and bind tospecific oligosaccharides. A few examples:
Concanavalin A and wheat germ agglutinin are
plant lectins that have been useful research tools.
Mannan-binding lectin (MBL) is a glycoproteinfound in blood plasma.
It associates with cell surface carbohydrates of
disease-causing microorganisms, promoting
phagocytosis of these organisms as part of the
immune response.