structure, properties and function of saccharidesvyuka-data.lf3.cuni.cz/cvse1m0001/structure... ·...
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Structure, properties and function of saccharidesVladimíra Kvasnicová
SACCHARIDES(carbohydrates, glycides)
= polyhydroxyaldehydesor
polyhydroxyketonesD-glucose D-fructose
•monosaccharides
•oligosaccharides
•polysaccharides
17 kJ/g
Saccharidesmonosaccharides:
C3 - glyceraldehyde (aldotriose), dihydroxyacetone (ketotriose); smallest saccharides, both are important intermediates of a human metabolism
C5 - ribose, 2-deoxyribose (aldopentoses); components of nucleotides: found in nucleic acids (ribose in RNA, deoxyribose in DNA)
C6 - glucose, galactose, mannose (aldohexoses), fructose (ketohexose); components of oligo- and-polysaccharides, metabolic intermediates
disaccharides (= oligosaccharides composed of 2 monosaccharides):
• sucrose (= saccharose) consists of glucose and fructose
• lactose (= milk sugar) consists of galactose and glucose
• maltose (= malt sugar) consists of two glucoses
polysaccharides (= glycans):
• starch = storage polysacharide of plants, consists of linear amylose and branched amylopectin; it is a glucan = polymer of glucose
• glycogen = storage polysaccharide of animal cells („animal starch“); it is a branched polymer of glucose (resembels amylopectin)
• cellulose = structural polysaccharide of plants, linear, water insoluble glucan
heteroglycosides = complex saccharides
• proteoglycans
• glycoproteins
• glycolipids
cellextracellular fluid
The figure has been adopted from: J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005
bacteria
These molecules contain also
non-sugar part (protein or lipid)
MONOSACCHARIDES
GLUCOSE – central role
The figures have been adopted from Harper´s Biochemistry a z http://www.vuw.ac.nz/staff/paul_teesdale-spittle/organic/chiral_web/images/fig1_5d.gif (April 2007)
chiral carbon
Saccharidesstructure of monosaccharides
• they contain one aldehyde group (aldoses) or one keto group - always at the 2nd carbon (ketoses) and two or more alcohol (hydroxy) groups
• the terminal hydroxy group (the last one in a molecule) is a „primary alcohol group“, it can be oxidized in two steps to carboxylic acid group
• all other hydroxy groups in a molecule (with exception of the first one in a molecule of ketose, which is also primary) are „secondary alcohol groups“
• aldehyde group can be either oxidized to a carboxylic acid group or reduced to a primary alcohol group; keto group can be only reduced, producing a secondary alcohol group (sugar-derived acids or sugar alcohols are formed)
• all carbons of a sugar molecule containing secondary alcohol groups are „chiral carbons“ (C*) - they form two possible spatial arrangements: with the alcohol group oriented either right or left
• a number of possible isomers of a monosaccharide can be calculated as 2n, where n = number of C* in the molecule; e.g. aldohexose contains 4 C*, so 24 = 16; it means that there are 16 different aldohexoses from which 8 are D-saccharides and 8 are L-saccharides (D- and L- saccharides are mirror images of each other); only one of these 16 isomers is called D-glucose
• ketoses contain by one C* less than aldoses (they have 2 primary alcohol gr.)
The figure is found at http://astrobiology.berkeley.edu/Mars101/pix/image003.jpg (April 2007)
The figure is found at http://webphysics.davidson.edu/Alumni/bedenius/liqcry/chiral.gif (April 2007)
number of isomers for n(C*) = 2n
n = 1, 2, 3, ...
Classification of monosaccharides
fructoseglucosehexoses (C6)
ribuloseribosepentoses (C5)
erythruloseerythrosetetroses (C4)
dihydroxyacetoneglyceraldehydetrioses (C3)
ketoses (>C=O)aldoses (-CHO)
Isomers of monosaccharides
The figures have been adopted from Harper´s Biochemistry
1) D- and L- izomers
= mirror images(enantiomers)
nature important:D-monosaccharides
2) pyranoses and furanoses
• pyranoses: aldohexoses
• furanoses: fructoseribose
glucopyranosepredominates
The figures have been adopted from Harper´s Biochemistry
3) αααα and ββββ anomers
only cyclicmolecules
• during dissolving of a saccharide in water the equilibrium between anomers is established = mutarotation(optical rotation of anomers is not the same)
ββββ-D-Glc
αααα-D-Glc
The figure is found at http://www.cbs.umn.edu/bmbb/brl/carb/CarbTJSA/Haworth/TwoAnomers.jpg (October 2007)
These isomers differ in an arrangement of the -OH group
formed by a cyclization of a monosaccharide.
The anomeric -OH group is the most reactive one in a molecule.
1) αααα-D-glucopyranose 2) ββββ-D-glucopyranose5) D-glucose
3) αααα-D-glucofuranose 4) ββββ-D-glucofuranose
All possible structures of glucose,
(2) predominates in aqueous solutions
4) aldo-/keto- isomers
aldose / ketose
glyceraldehyde / dihydroxyacetone
ribose / ribulose
glucose /fructose
The figures have been adopted from Harper´s Biochemistry
5) epimers
= isomers of saccharides differing in orientation of only one –OHgroup in space
Man = 2-epimer of Glc
Gal = 4-epimer of Glc
The figures have been adopted from Harper´s Biochemistry
The figures have been adopted from Harper´s Biochemistry
Gal is found in lactose (milk sugar)
Gal and Man and their derivatives
are found inheteroglycosides
Physiologically important monosaccharides
ALDOSES
The figures have been adopted from Harper´s Biochemistry
KETOSES
The figures have been adopted from Harper´s Biochemistry
Physiologically important monosaccharides
Derivates of monosaccharides
1) sugar alcohols are formed by reduction of the carbonyl group
glucose → glucitol (= sorbitol)
fructose
mannose → mannitol
galactose → galactitol
D-Glucitol
2) oxidation of saccharides produces acids:
• aldaric acids (glucaric)both C1 and C6 is oxidized = dicarboxylic a.
• aldonic acids (gluconic)oxidation of C1
• alduronic (glucuronic)oxidation of C6
3) deoxysaccharides are formed by reduction of secondary –OH group
2-deoxy-D-ribose
4) amino saccharides contain one amino group instead of one –OH group
D-glucose amine
The figures have been adopted from Harper´s Biochemistry
The figure has been adopted from J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005
amino saccharides are often acetylated
(found in heteroglycosides)
5) esters are formed by esterification
• with H3PO4
(intermediatesof metabolism)
• with H2SO4 (foundin proteoglycans)
The figure has been adopted from J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005
(ester is formed by a reaction of an alcohol group with an acid)
6) glycosides are formedby reaction with alcoholsor amines
• O-glycosidic bond(oligo and polysaccharides,
connection to proteins)
• N-glycosidic bond(in nucleic acids,connection to proteins)
The figure has been adopted from J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005
The figure is found at http://www.nmc.edu/~koverbaugh/bio115/Image14.gif (October 2007)
O-glycosidic bond
The figure is found at http://www.thebestlinks.com/images/f/f5/ATP.png (October 2007)
N-glycosidic bond
Adenosine triphosphate (ATP)
ribose
DISACCHARIDES
SALAME
• SAcharose (= sucrose)
• LActose
• MaltosE
saccharose has not reducing properties
The figure has been adopted from J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005
α-Glc(1→4)Glc β-Gal(1→4)Glc α-Glc(1→2)β- Fru
free anomeric (= hemiacetal) hydroxyl ⇒ reducing properties
Numbers in parenthesis denote which carbon of each sugar is involved in the bond
POLYSACCHARIDES
• homopolysaccharidesstarch, glycogen, cellulose, inuline
• heteropolysaccharidesglycoproteins, proteoglycans
• branched
• unbranched
• storagestarch, glycogen,inuline
• structuralcellulose, proteoglycans
amylose (maltose)n amylopectine
STARCH (Glc)n
The figures have been adopted from Harper´s Biochemistry
α(1→4) glycosidic bonds α(1→4) glycosidic bonds
α(1→6) glycosidic bonds
GLYCOGEN (Glc)n
The figure is found at http://students.ou.edu/R/Ben.A.Rodriguez-1/glycogen.gif (October 2007)
nonreducing end reducing end
OH
(anomeric -OH group is blocked by the bond) (anomeric -OH group is free: the aldehyde group can reconstitute after opening the cycle of the sugar)
CELLULOSE
ββββ-Glc(1→4)Glc
The figures are found at http://web.chemistry.gatech.edu/~williams/bCourse_Information/6521/carbo/glu/cellulose_int_2.jpghttp://www.kjemi.uio.no/14_skole/modul/Evina_organisk/Org_K3fig14_cellulose.JPG (October 2007)
The figure is found at http://www.grandmeadows.com/archives/truth1.gif (October 2007)
PROTEOGLYCANS
core protein
+glycosaminoglycans
(GAG)
(aminosugar-uronic acid)nGAG is a polymer of these sugar derivatives
http://departments.oxy.edu/biology/Stillman/bi322/030101/F9_23.gif (October 2008)
The figure has been adopted from J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005
GLYCOPROTEINS