carbohidratos-ppt
TRANSCRIPT
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Química de carbohidratos
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2.5 Química de carbohidratosa. Monosacáridos, disacáridosb. Polisacáridos de reservac. Polisacáridos estructuralesd. Mucopolisacáridos
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Carbohidratos
•Pertenecen al grupo de biomoléculas mas abundantes: Carbohidratos, Proteínas, Lípidos y Acidos Nucléicos
•Químicamente se definen como aldehidos o cetonas polihidroxiladas
•La materia orgánica mas abundante sobre la tierra
Photosynthesis converts morethan 109 metric tons of CO2 and H2O into celluloseand other plant products.
the word “saccharide” is derived from the Greek sakcharonsakcharon, meaning “sugar”, a sweet crystaline substance derived from plants
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•Función :
Almacén de energía, combustibles e intemediarios metabólicos
Ribosa y desoxiribosa, componentes esenciales de RNA y DNA
Almidón y celulosa
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Elementos estructurales en paredes celulares de bacterias y plantas.
Reconocimiento o anclaje molecular
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Diversidad estructural en carbohidratos :
Propiedad clave que determina su papel como mediadores de interacciones celulares
Construidos a partir de unidades de azúcares (monosacáridos) C3-C9
Tamaño, secuencia y estereoquímica definida
Unión (N-gly, , , ....) y composición molecular específica
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Monosacáridos: los azúcares mas simples
Aldehidos o cetonas con uno o mas grupos hidroxilo
Formula general Cn(H2O)m donde n, m pueden ser iguales o diferentes y ≥ 3
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If the carbonyl group is at an end of the carbon chain (aldehyde group) the monosaccharide is an aldose
Glyceraldehyde has a single asymmetric carbon and, thus, there are two stereoisomers of this sugar generating two series of aldoses D-aldosas y L-aldosas.
D-glyceraldehyde and L-glyceraldehyde are enantiomers, or mirror images of each other
If the carbonyl group is at any other position (ketone group) the monosaccharide is a ketose.
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C3
C4
C5
C6
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C3
C4
C5
C6
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Glyceraldehyde and dihydroxyacetone are referred to as trioses
Simple monosaccharides with four, five, six, and seven carbon atoms are called tetroses, pentoses, hexoses, and heptoses, respectively.
Because these molecules have multiple asymmetric carbons, they exist as diastereoisomers, isomers that are not mirror images of each other, as well as enantiomers.
Sedoheptulosa
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Neuraminic acid
Sialic acid
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The symbols D and L designate the absolute configuration of the asymmetric carbon farthest from the aldehyde or keto group.
Enantiomers : non-superimposable COMPLETE mirror images
Epimers: sugars that differ in configuration at ONLY 1 POSITION
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Two sugars that differ only in the configuration around one carbon atom are called epimers.
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Monosaccharides with four, five, six, and seven carbon atoms in their backbones are called, respectively, tetroses, pentoses, hexoses, and heptoses.
a) There are aldoses and ketoses of each of these chain lengths: aldotetroses and ketotetroses, aldopentoses and ketopentoses, and so on.
b) The hexoses, which include the aldohexose D-glucose and the ketohexose D-fructose, are the most common monosaccharides in nature.
c) The aldopentoses D-ribose and 2-deoxy-D-ribose are components of nucleotides and nucleic acids.
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Three ways to represent the two stereoisomers of glyceraldehyde.
The stereoisomers are mirror images of each other. Ball and-stick models show the actual configuration of molecules.
By convention, in Fischer projection formulas, horizontal bonds project out of the plane of the paper, toward the reader; vertical bonds project behind the plane of the paper, away from the reader.
Recall that in perspective formulas, solid wedge-shaped bonds point toward the reader, dashed wedges point away.
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Formation of hemiacetals and hemiketals.An aldehyde or ketone can react with an alcohol in a 1:1 ratio to yield a hemiacetal or hemiketal. A new chiral center at the carbonyl carbon is created. Substitution of a second alcohol molecule produces an acetal or ketal. When the second alcohol is part of another sugar molecule, the bond produced is aglycosidic bond
In Solution, The Common Monosaccharides Have Cyclic Structures
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The keto group in the open chain form of a ketohexose such as fructose, can form an intramolecular hemiketal by reacting with either the C-6hydroxyl group to form a six-membered cyclic hemiketal (pyranose) or the C-5 hydroxyl group of to form a five-membered cyclyc hemiketal(furanose)
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Two cyclic forms of D-glucose. Reactionbetween the aldehyde group at C-1 and the hydroxyl group at C-5 forms a hemiacetal linkage, producing either of two stereoisomers, the and anomers, which differ only in the stereochemistry around the hemiacetal carbon.
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The interconversion of and anomers is called mutarotation.
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Son aquellos azúcares que poseen al menos un carbonilo (grupo funcional) intacto, es decir no formando ni cetal o acetal.
Azúcares que en solución alcalina forman un aldehido o cetona
Reductores: Glucosa, fructosa, gliceraldehido, lactosa, arabinosa, maltosa…..
No reductores: Sacarosa, trealosa
Las cetosas no se oxidan directamente, mas bien al transformarse en aldehidos por tautomerismo ceto-enólico
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Conformational formulas of pyranoses. (a) Two chair forms of the pyranose ring. Substituents on the ring carbons may be either axial (ax), projecting parallel to the vertical axis through the ring, or equatorial (eq), projecting roughly perpendicular to this axis. Two conformers such are these are not readily interconvertible without breaking the ring. However, when the molecule is “stretched” (by atomic force microscopy), an input of about 46 kJ of energy per mole of sugar can force the interconversion of chair forms. Generally, substituents in the equatorial positions are less sterically hindered by neighboring substituents, and conformers with bulky substituents in equatorial positions are favored.
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Tautomerismo ceto-enólico
Tautomerismo ceto-enólico en fructosa bajo condiciones alcalinas
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Disacáridos
•Carbono anómericode un azucar se une a –OH de otro azúcar formando enlace O-glicosídico
•Enlace N-glicosídico C-anomérico => N de proteína, nucleótido o azúcar
•Sensibles a hidrólisis ácida y resistentes a hidrólisis básica
•Extremo reductor, presencia de carbonilo intacto, no formando ni cetal o acetal.
Maltosaα-D-Glucopyranosyl-
(1→4)-D-glucose
Sacarosaβ-D-fructofuranosyl-(2→1)-α-D-glucopyranoside
Lactosaβ-D-galactopyranosyl-(1→4)-D-glucose
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Maltosa
Configuración α de carbono anomérico, forma enlace α
The glucose residue with the free anomeric carbon is capable of existing in - and -pyranose forms
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Kojibiosa α(1→2)
Isómeros α de maltosa (Glc-Glc)
Maltosa α(1→4)
Nigerosa α(1→3)
Isomaltosa α(1→6)
Trealosa α(1→1)
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Isómeros de maltosa
celobiosa (1→4)
Soforosa (1→2)Laminaribiosa (1→3)
Gentobiosa (1→6)
,-Trealosa (1→1)
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Polisacáridos
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lineal homogéneo
ramificado homogéneo
alternado
bloques
lineal heterogéneo
ramificado heterogéneo
interumpido ramificado
Polisacáridos
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Glicógeno glucosa α-(1-4) ramificado en α-(1-6) cada 8-12 résidus
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Almidón, formado por dos homopolímeros, amilosa (no ramificada α-(1-4)) y amilo pectina (ramificado en α-(1-6) cada 24-30 résiduos)
amilosa no ramificada α-(1-4)
amilo pectina ramificada en α-(1-6) cada 24-30 résiduos
Almidón : motivo de repetición la maltosa
Celulosa : motivo de repetición la celobiosa
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Hélices abiertas mejor almacén de energía
Cadenas lineales mejor soporte estructural
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