Types of Carbohydrates Classification of Monosaccharides D and L Notations from Fischer Projections Structures of Some Important Monosaccharides.
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Types of Carbohydrates Classification of Monosaccharides D and L Notations from Fischer Projections Structures of Some Important Monosaccharides
Carbohydrates
CarbohydratesCarbohydrates are: A major source of energy from our diet. Composed of the elements C, H and O. Also called saccharides, which means
“sugars”. Produced by photosynthesis in plants.
Photosynthesis in plants requires CO2, H2O, and energy from the sun and produces carbohydrates, such as glucose
[C6H12O6 = C(H2O)6].
In respiration, glucose is oxidized in living cells to produce CO2, H2O, and energy.
Photosynthesis and Respiration
Types of Carbohydrates
Monosaccharides are the simplest carbohydrates.
Disaccharides consist of two monosaccharides.
Polysaccharides contain many monosaccharides.
Most of the names of carbohydrates end in -ose
Glucose-What plants make Maltose- used in making beer (disaccharide) Fructose – found in fruit (monosaccharide) Sucrose- Table sugar (disaccharide) Lactose – In milk (disaccharide)
Classification of Monosaccharides
Aldoses are monosaccharides with an aldehyde group and many hydroxyl (-OH) groups.
Ketoses are monosaccharides with a ketone group and many hydroxyl (-OH) groups.
CHO
HO H
CH2OH
CHO
HO H
OHH
CH2OH
CH2OH
O
HHO
OHH
OH H
OH
AldoseAldose Ketose
Monosaccharides Monosaccharides are also classified according to the number of carbon atoms.
A triose has three carbons; a tetrose has four carbons; a pentose has five carbons; and a hexose has six carbons.
CHO
HO H
CH2OH
CHO
HO H
OHH
CH2OH
CH2OH
O
HHO
OHH
OH H
OH
Triose Tetrose Hexose
Th
e t
wo s
imp
lest
sug
ars 2
|1—C—3 | 4
2 |3—C—1 | 4
Note Numerous Chiral Carbons
Fischer Projection a two-dimensional representation of the three-
dimensional structure of organic molecules. usually used to represent the molecular structures of
monosaccharides and amino acids. devised by Hermann Emil Fischer in 1891.
Haworth Projection a common way of representing the
cyclic structure of monosaccharides with a simple three-dimensional perspective.
was named after the English chemist Sir Walter N. Haworth.
Fischer Projections Is used to represent carbohydrates. Places the most oxidized group at the top. Uses horizontal lines for bonds that come forward. Uses vertical lines for bonds that go back.
D and L Notations
By convention, the letter L is assigned to the structure with the —OH on the left.
The letter D is assigned to the structure with —OH on the right.
D and L Monosaccharides The —OH on the chiral atom farthest from the
carbonyl group is used to assign the D or L configuration.
The D form is usually the isomer found in nature.
L-Galactose
C
HO H
OHH
OHH
HHO
CH2OH
O
OHC
H OH
HHO
OHH
OHH
CH2OH
O
D-Glucose
HCHO
H OH
OHH
OHH
CH2OH
D-Ribose
D-Glucose Found in fruits, corn syrup, and honey.
An aldohexose with the formula C6H12O6
Known as blood sugar in the body.
Blood Glucose Level
In the body, glucose has a normal concentration of 80-110 mg/dL.
In a glucose tolerance test, blood glucose is measured for several hours after ingesting glucose.
D-Fructose
D-Fructose
CH2OH
C
C
O
C
H
OHH
HO
C
CH2OH
OHH
Is a ketohexose with formula of C6H12O6.
Is the sweetest carbohydrate. Is found in fruit, juices and
honey. Converts to glucose in the
body.
D-Galactose
Is not found free in nature.
Is obtained from lactose, a disaccharide.
Is important in cellular membranes.
CHO
C
C
OH
C
H
HHO
HO
C
CH2OH
OHH
H
D-Galactose
Cyclic Structures
Monosaccharides with 5-6 carbon atoms form cyclic structures
The hydroxyl group on C-5 reacts with the aldehyde group or ketone group
o O
Sugars Prefer To Be Cyclic
Haworth Structure for D-Isomers
The cyclic structure of a D-isomer has the final CH2OH group located above the ring.
oCH2OH
Numbered carbons
C
CC
C
CC
1'
2'3'
4'
5'
6'
O
Haworth Structure for D-Glucose
The new –OH on C1 has two possibilites: down for anomer, up for anomer
• Isomers that differ only in their configuration about the new asymmetric carbon are called anomers, the carbonyl carbon is called anomeric carbon.
• α-anomer • β-anomer
Cyclic Haworth Structures
Stable cyclic hemiacetals form when the C=O group and the
-OH are part of the same molecule.
For hexoses, the hydroxyl group on C-5 reacts with the aldehyde group or ketone group.
The cyclic structure of a D-isomer has the last CH2OH group located above the ring.
oCH2OH
Formation of Cyclic Glucose The Haworth structure can be written from the
Fischer Projection.
The –OH group on the left (C3) is drawn up.
The –OH groups on the right (C2, C4) are drawn down.
Haworth Structure for D-Glucose
oCH2OH
OHOH
OH
OH
oCH2OH
OHOH
OH
OH
-D-Glucose -D-Glucose
Glucose Anomers
OH
OH
OH
CH2OH
CHO
OHO
CH2OH
HH
OHH
OH
OH
HH
OH
D-(+)-glucose
UP
DOWN
on right = D
CONVERTING TO HAWORTH PROJECTIONS
-CH2OH up = D cis
= b
FISCHERPROJECTION
trans
= a
HAWORTHPROJECTIONS
O
CH2OH
HH
OHH
OH
OH
HOH
H
BOTH ANOMERS OFA D-SUGAR(D-glucose)
1
6
2
3
4
5
1
23
4
6
5
Mutarotation
• A small amount of open chain is in equilibrium with the cyclic forms.
• The most stable form of glucose is β-D-glucose.
-D-glucose D-glucose (open) β-D-glucose (36%) (trace) (64%)
-D-Glucose
and are “anomers” and differ in configuration at the new chiral center formed in the cycle
In nature, open chain forms are rare. All 5 forms coexist with the pyranose forms
occurring 99% of the time, furanose about 0.5% each and a trace of open chain
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