Carbohydrate
Transcript of Carbohydrate
Carbohydrates
Outline
Introduction
Monosaccharides
Disaccharides and Oligosaccharides
Polysaccharides
Acidic polysaccharides
Introduction
NameTriose Tetrose Pentose HexoseHeptose
Formula C3H6O3
C4H8O4 C5H10O5 C6H12O6
C7H14O7
Monosacchrides
Formula CnH2nOn n=3-8
Structure and nomenclature
Aldose - aldehyde/hydroxyl
Ketose – ketone/hydroxyl
D and L Monosaccharides
Fischer Projection Formulas
In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde
D-monosaccharide:D-monosaccharide: the -OH on its penultimate (next to last) carbon is on the right
L-monosaccharide:L-monosaccharide: the -OH on its penultimate (next to last) carbon is on the left
Amino sugars
Contain an –NH2 group in place of –OH group
Only three amino sugars
Glucose is produced in plants from CO2 and
H2O via photosynthesis.
Plants convert glucose into other small sugars
and polymers (cellulose, starch).
Dietary carbohydrates provide the major
source of energy required by organisms.
Physical properties
Colorless,crystalline solid
Are very soluble in water
Sightly soluble in ethanol
Insoluble in non-polar solvent diethyl ether,
chloro-form,benzene….
The Cyclic Structure of Monosaccharide
Aldehydes and ketones react with alcohols to form hemiacetalshemiacetals Cyclic hemiacetals form readily when the hydroxyl and
carbonyl groups are part of the same molecule and their interaction can form a five- or six-membered ring
For example:
O-HH
O
CO O
H
H
O O-H
H4-Hydroxypentanal
A cyclic hemiacetal
14
14
redraw to show -OH and -CHO
close to each other
The Cyclic Structure of Monosaccharide
A. Haworth Projections The cyclic structure of monosaccharide is
the
Haworth projection D-Glucose forms these cyclic hemiacetalsCHO
OH
H
OH
H
HO
H
H OH
CH2OH
HH OH
HHO
HOH
OH
H
CH2OHO
C
H OH
HHO
HOH
H
CH2OHOH
O
H
OHH OH
HHO
HH
OH
H
CH2OHO
D-Glucose
-D-Glucopyranose (-D-Glucose)
()
()
-D-Glucopyranose (-D-Glucose)
+
anomericcarbon
5
5
1
1
redraw to show the -OH on carbon-5 close to thealdehyde on carbon-1
The Cyclic Structure of Monosaccharide
A. Haworth Projections
Cyclic hemiacetal is represented as a planar ring, lying roughly perpendicular to the plane of the paper
Groups bonded to the carbons of the ring then lie either above or below the plane of the ring
New carbon stereocenter created in forming the cyclic structure is called an anomeric carbonanomeric carbon
Stereoisomers that differ in configuration only at the anomeric carbon are called anomersanomers
Anomeric carbon of an aldose is carbon 1; that of the most common ketoses is carbon 2.
The Cyclic Structure of Monosaccharide
A. Haworth Projections form: -OH on the anomeric carbon is
on the same side of the ring as the terminal –CH2OH (up)
form: -OH on the anomeric carbon is on the side of the ring opposite from the terminal –CH2OH (down)
Pyranose:Pyranose: 6-member ring sugar containing O
Furanose:Furanose: 5-member ring sugar containing O
PyranFuranOO
The Cyclic Structure of Monosaccharide
A. Haworth ProjectionsD-fructose also forms a five-membered cyclic
hemiacetal
HO
HOCH2 OH
HHO
CH2OH
OHH
H
C=O
CH2OH
HOH
CH2OH
OHH
HO HOH
HOHOCH2
HO HCH2OH
OH
D-Fructose
1
2
5
5
5
1
2
2
()
-D-Fructofuranose(-D-Fructose)
-D-Fructofuranose(-D-Fructose)
()
1
The Cyclic Structure of Monosaccharide
B. Conformation Representations
For pyranoses, the six-membered ring is more accurately represented as a chair conformationchair conformation
OCH2OH
HOHO
OHOH()
CHOH
HO
CH2OHOHHO
OHO
OH()HO
HO
CH2OHO
(-D-Glucose)
(-D-Glucose)
-D-Glucopyranose
-D-Glucopyranose
D-Glucose
anomericcarbon
The Cyclic Structure of Monosaccharide
B. Conformation RepresentationsThe Haworth projection and the chair
conformation, the orientations of groups on carbons 1- 5 of -D-glucopyranose are up, down, up, down, and up
OCH2OH
HOHO
OHOH()H
H OH
HHO
HOH()
OH
H
CH2OHO
-D-Glucopyranose(chair conformation)
-D-Glucopyranose(Haworth projection)
123
4
5
6
1
23
4
5
6
The Cyclic Structure of Monosaccharide
C. Mutarotation
Mutarotation:Mutarotation: a- and b-anomers can have the ring open and then form the other anomer.A change in specific optical rotation accompanies the equilibration of in aqueous solution Example: when either a-D-glucose or b-D-glucose is dissolved in water, the specific rotation of the solution gradually changes to an equilibrium value of +52.7°, which corresponds to 64% beta and 36% alpha forms
The Cyclic Structure of Monosaccharide
C. Mutarotation
[]D25 = + 18.7°
-D-Glucopyranose-D-Glucopyranose[]D
25 = +112°
OHOH
HOHO
CH2OHO HO OH
OC
CH2OH
HO
HOH
OCH2OH
HO
HOOH
HO
Open-chain form
The Cyclic Structure of Monosaccharide
C. Mutarotation
Rings can open to form open chain compound. New ring can be either - or -anomer Equilibrium among - and - forms (and open chain) will be established. Change in specific optical rotation accompanies this equilibration
If either -D-glucose or -D-glucose is dissolved in water, specific rotation changes to an equilibrium value of +52.7° 64% beta and 36% alpha forms at equilibrium Very little will exist in open chain form
The Cyclic Structure of Monosaccharide
C. Mutarotation
Another representation of ring opening and closure
The Cyclic Structure of Monosaccharide
C. Mutarotation
D-Glucose- a cyclic monosaccharideOHOCH2
OHOH
OHOH
OHOCH2
OHOH
OH
OH
OHHOCH2
OHOH
OHO
H
-D-glucopyranone Open Chain -D-glucopyranone
[] +18.70 +1120
Equilibrium 64% 36%
Mutorotation: Change in specific rotation that accompanies the interconversion of and - anomers in water.
Reaction Of Monosaccharides
A. Fromation of Glycosides (Acetals) The cyclic hemiacetal form of a sugar can react
with an alcohol in the presence of acid to form an acetal
Glycoside: a cyclic acetal derived from a monosaccharideGlycosidic bond: the bond from the anomeric carbon to
the –OR group
Glycosides: are named by the name of the carbonhydrates in which the ending –e is replaceed by –ide.
Example:
acetals of glucose glucosides
acetals of maltose maltosides
ketals of fructonse fructonsides
Just as the anomeric carbon of a cyclic hemiacetal undergoes reaction with the -OH group of an alcohol to form a glycoside, it also undergoes reaction with the N-H group of an amine to form an N-glycoside.
N-Glycosides of these pyrimidine and purine bases are structural units of nucleic acids
Hemi-acetal
O
H
HH
H
OH
OH
H OH
OH
OH
NH
NH
O
O O
H
HH
H
OH
OH
H OH
OH
N
NH
O
O
N-glycoside
B. Reduction of Monosaccharides
Aldoses( and ketoses) can be reduced with sodium borohydride to compounds called alditols
Sorbitolis used in the manufacture of candies and as a sugar substitute for diabetics. D-Sorbitol is an important food additive, usually added to prevent dehydration of foods and other materials on exposure to air
C. Oxidation to Aldonic Acids
Oxidizing agents such as oxygen (O2), Tollens' reagent (Ag+, NH3), Fehling's reagent (Cu2+, sodium tartrate), Benedict`s reagent (Cu2+ sodium citrate) will oxidize aldehydes to give carboxylic acids
Ketones cannot be oxidized like aldehydesKetoses are reducing sugars if they can isomerize
to aldoses
D. Oxidation to Uronic acid
We learned that primary alcohols can be oxidized to carboxylic acids. Hexoses contain a primary alcohol at C6 which can be oxidized to a carboxylic acid by various enzymes in plants and animals
CHO
OH
OH
H
OHH
HO
H
H
CH2OH
CHO
OH
OH
H
OHH
HO
H
H
COOH
O
CHOOH
OH
OHHO
HO
Enzyme-catalyzedoxidation
CHO
OH
OH
H
OHH
HO
H
H
CH2OH
E. Oxidation by periodic acid
In this reaction, iodine (VII) of periodic acid is
reduced to iodine (V) of iodic acid.
Disaccharides and Oligosaccharides
Disaccharide: A carbohydrate containing two
monosaccharide units joined by a glycosidic bond.
Oligosaccharide: A carbohydrate containing four to
ten monosaccharide units, each joined to the next by a
glycosidic bond.
Maltose
Lactose is a sugar that is found most notably in milk. Lactose makes up around 2~8% of milk (by weight), although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from lac, the latin word for milk, plus the -ose ending used to name sugars. It has a formula of C12H22O11.
Structure:
When 1 mol of maltose is subjected to acid-catalyzed
hydrolysis, it yield 2 mol of D-(+)-glucose.
Maltose is a reducing sugar.
Maltose exists in two anomeric forms: α-(+)-maltose, and
β-(+)-maltose
Maltose reacts with bromine water to form a
monocarboxylic acid, maltose acid.
Methylation of maltose acid followed by hydrolysis gives
2,3,4,6-tetra-O-methyl-D-glucose and 2,3,5,6-tetra-O-
methyl-D-gluconic acid.
Methylation of maltose itself, followed by hydrolysis,
gives 2,3,4,6-tetra-O-methyl-D-glucose and 2,3,4,6-tri-O-
methyl-D-glucose.
Sucrose
Sucrose: the most widely occurring disaccharide of ordinary table sugar
Structure:
Sucrose has the molecular formula C12H22O11 Acid-catalyzed hydrolysis of 1 mol of sucrose
yields 1 mol of D-glucose and 1 mol of D-fructose. Sucrose is a nonreducing sugar. Neither the
glucose not the fructose portion of sucrose has a hemiacetal or hemiketal group, thus the two hexoses must have a glycoside linkage that involves C-1of glucose and C-2 of fructose.
The hydrolysis of sucrose indicates an α configuration at the glucoside portion and an enzyme known to hydrolyze a β-fructofuranosides.
Methylation of sucrose gives an octamethyl derivative that, on hydrolysis, gives 2,3,4,6-tetra-O-methyl-D-glucose and 1,3,4,6-tetra-O-methyl-D-fructose
Lactose
Lactose is a reducing sugar that hydrolyzes to yield D-glucose and D-galactose; the glycosidic linkage is β.
Structure:
Polysaccharides
Have a general formula of Cx(H2O)y (x:200-2500) or (C6H10O5)n (40n3000).
Are polymeric carbohydrate structure.
Consist of large numbers of monosaccharide units bonded together by glycosidic bonds ( it is formed between the hemiacetal group of a saccharide and the hydroxyl group of some organic compound such as an alcohol).
These structure are often linear, but may contain various degrees of branching.
Are often quite heterogeneous.
Three important polysaccharide are starch, glycogen and cellulose.
Starch
Is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds.
Is used for energy storage in plants.
Consists of two types of molecules: the linear and helical amylose and the branched amylopectin.
Contain 20-25% amylose and 75-80% amylopectin.
Pure starch is white, tasteless and odorless powder, insoluble in cold water or alcohol, but soluble in heated water
Amylose
Is composed of unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds.
Figure . Amylopectin
Amylopectin
Contains chains up to 10000 D-glucose units joined by -1,4-glycosidic bonds.
At branch points, new chains of 24 to 30 units are started by -1,6-glycosidic bonds.
H2CO
HOOH
O
6
41
O
OHOH2C
OHO
OOH
41
O
OH
HOH2C
OHO
O
HO
HOH2C
OOH
4
1
4
-glycosidic bond
-1,4-glycosidic bonds
Applications of starch
Glycogen
Is the energy-reserve carbohydrate for animals.
Is a branched polysaccharide of approximately
106 glucose units joined by -1,4- and -1,6-
glycosidic bonds.
Divided almost equally between liver and
muscle.
Cellulose
Figure . Cellulose.
O
CH2OH
OHO
OH
O OHO
OH
HOH2C
OOHO
HOH2C
OH
O O
HO
CH2OH
HO1
4
1 4
1 4
-1,4-glycosidic bonds
Has the formula (C6H10O5)n.
Is a linear polysaccharide of D-glucose units joined by -1,4-glycosidic bonds.
Has an average molecular weight of 400000g/mol.
Is the structural component of the primary cell wall of green plants, many forms of algae,...
Has no taste, is odourless, is hydrophilic, is insoluble in water and most organic solvents.
Humans and other animals have only -glucosidases in digestion system no use cellulose as food
Textile fibers from cellulose
Cotton is almost pure cellulose.
Both rayon and acetate rayon are made from chemically modified cellulose and were the first commercially important synthetic textile fibers.
In the production of rayon:
Cellulose-OHNaOH
Cellulose- O NaS=C=S
Cellulose-O-S-S Na
San -OH group in a cellulose fiber
Sodium salt of a xanthate ester (a viscous colloidal suspension)
Cellulose (insoluble in water)
:
In the industrial synthesis of acetate rayon, cellulose is treated with acetic anhydride.
OOHO
H2C
OH
O
OH
+3CH3COCCH3
O O
OO
H2C
O
O
CCH3
O
OCCH3
CH3CO
O
O
+ CH3COOH
A glucose unit in a cellulose fiber
Acetic anhydride
A fully acetylated glucose unit
Acidic Polysaccharide
A group of polysaccharides contain carboxyl
groups and/or sulfuric ester groups.
Play important roles in the structure and
function of connective tissue.
There is no single general type of connective
tissue.
Hyaluronic Acid
Is the simplest acidic polysaccharide present in connective tissue.
Has a molecular weight of between 105 and 107g/mol.
Contains from 3000-100000 repeating units.
Is most abundant in embryonic tissues and in specialized connective tissue such as the vitreous humor of eye, the lubricant of joints in the body,...
OHO
-OOC
OH
O OHO
HOH2C
NH
O*
H3C O
3 1 3
4
1
4*
D-glucuronic acid N-acetyl-D-glucosamine
The repeating unit of hyaluronic acid
The repeating disaccharide unit in hyaluronic acid is D-glucuronic acid linked by a -1,3-glucosidic bond to N-acetyl-D-glucosamine.
Heparin
Is a heterogeneous mixture of variably sulfonated polysaccharide chains.
Molecular weight from 6000-30000g/mol.
Is synthesized and stored in mast cell of various tissues: liver, lungs and gut.
Is widely as an injectable anticoagulant.
Binds strongly to antithrombin III.
OHO
O
H2C
OSO3-
ONH
C
CH3
O
OHO
-OOC
OH
OO
O
-O3S
H2C
OH
NH
SO3-
O
O
HO OSO3-
O
COO-
OH2C
OSO3-
ONH
SO3-
HO
The repeating monosaccharide units of heparin are N-acetyl-D-glucosamine, D-glucuronic acid, D-glucosamine, and L-ioduronic acid bonded by a combination of -1,4- and -1,4-glycosidic bonds.
A pentasaccharide unit of heparin.
http://en.wikipedia.org/wiki/Heparin
http://en.wikipedia.org/wiki/Hyaluronan
http://en.wikipedia.org/wiki/Glycogen
http://vi.wikipedia.org/wiki/Cellulose
http://en.wikipedia.org/wiki/Glycosidic_bond
http://www.daviddarling.info/encyclopedia/P/polysaccharide.html
http://vi.wikipedia.org/wiki/Tinh_b%E1%BB%99t
References