Bioquímica- 1 carbohidratos

7/29/2019 Bioqumica- 1 carbohidratos

1/27

Carbohydrates

Copyright 1999-2005 by Joyce J. Diwan.

All rights reserved.

Molecular Biochemistry I


2/27

EL PRINCIPAL CICLO ENERGTICO DE LA BISFERA:Fotosntesis y Respiracin.


3/27

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


4/27

CHOs REPRESENTATIVOS: MONO-, DI- Y POLI-SACRIDO(MONMERO, OLIGMERO Y POLMERO)


5/27

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


6/27

TRIOSAS, LOS MONOSCARIDOSMS SENCILLOS

INTERCONVERSIN TAUTOMRICA ALDOSA-CETOSA

ENANTIMEROS DELGLICERALDEHIDO

* TAUTMEROS. Ismerosestructurales que difieren en la

distribucin de sus H y =

* ENANTIMEROS:ISMEROS PTICOS


7/27

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


8/27

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


9/27

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)


10/27

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


11/27


12/27

DIASTERMEROSDE TETROSAS


13/27

PRESENCIA Y FUNCIONES BIOQUMICAS DE LOS MONOSACRIDOS


14/27

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

+

+


15/27

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)


16/27

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


17/27

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


18/27

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


19/27

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


20/27

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


21/27

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


22/27

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


23/27

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.


24/27

These microfibrils arevery strong.The role of cellulose isto impart strength andrigidity to plant cellwalls, which can

withstand highhydrostatic pressuregradients. Osmoticswelling is prevented.


25/27

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.


26/27

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.


27/27

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.

Documents

Bioquímica- 1 carbohidratos