Carbohydrates linco larry

Carbohydrates

Scheffler
LincoLarry Jln High School
2008
Version 1.10


Carbohydrates
• Contain Carbon, Hydrogen and Oxygen

• Can be characterized as
– Monosaccharides
– Disaccharides
– Polysaccharides
• Includes sugars, starches, cellulose,


Carbohydrates
Produced by plants during
photosynthesis; contains C, H, O

Monosaccharides

Single (simple) sugars; quick energy
Contain C, H, and O in 1:2:1 ratio
Examples:
Glucose C6H12O6
Fructose C6H12O6
Galactose C6H12O6
glucose

fructose


Types of Carbohydrates
Carbohydrates have the following basic composition:
I
(CH2O)n or H - C - OH
I
 Monosaccharides - simple sugars with multiple OH
groups. 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 covalently
linked.
 Polysaccharides - polymers consisting of chains of
monosaccharide or disaccharide units.


Monosaccharides
• Empirical formula is CH2O
• Open chain and ring structures are possible
• Many structural isomers are possible
• The most common forms have:
– Five carbons C5H10O5 - called pentoses
– Six carbons C6H12O6 - called hexoses
• Contain at least one carbonyl group C=O.
• If the carbonyl group is at the end it is an aldose sugar.
• If it is within the chain it is a ketose sugar

• Multiple chiral carbon atoms lead to optical isomers
• Usually have between 3 and 6 carbon atoms


Monosaccharides
Aldoses (e.g., glucose)
have an aldehyde group
at one end.
H

C

Ketoses (e.g., fructose)
have a ketone group,
usually at C2.

O

CH2OH
C

O

HO

C

H

OH

H

C

OH

OH

H

C

OH

H

C

OH

HO

C

H

H

C

H

C

CH2OH

CH2OH

D-glucose

D-fructose


Optical Isomers: D and L
D or dextrorotatory &
L or levorotatory are
designations for
optical isomers that
are based on the
configuration about
the single asymmetric
C in glyceraldehyde.
The lower
representations are
Fischer Projections.

CHO

CHO

H

C

OH

HO

L-glyceraldehyde

CHO
H

C

OH

CH2OH

D-glyceraldehyde

H

CH2OH

CH2OH

D-glyceraldehyde

C

CHO
HO

C

H

CH2OH

L-glyceraldehyde


Sugar Nomenclature
For sugars with
more than one chiral
center, D or L refers
to the asymmetric C
farthest from the
aldehyde or keto
group.
Most naturally
occurring sugars are
D isomers.

O

H

C

H – C – OH
HO – C – H
H – C – OH
H – C – OH
CH2OH
D-glucose

O

H

C
HO – C – H
H – C – OH
HO – C – H
HO – C – H
CH2OH
L-glucose


Steroisomers
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.

O

H

C
H – C – OH
HO – C – H
H – C – OH
H – C – OH
CH2OH
D-glucose

O

H

C
HO – C – H
H – C – OH
HO – C – H
HO – C – H
CH2OH
L-glucose

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 Lsugars).

Ring Structures
Pentoses and
hexoses can form
ring structures as
the ketone or
aldehyde reacts
with a distal OH.
Glucose forms an
intra-molecular
hemiacetal, as the
C1 aldehyde & C5
OH react, to form
a 6-member ring
known as a
pyranose ring,

1

H
HO
H
H

2
3
4
5
6

CHO
C

OH

C

H

C

OH (linear form)

C

OH

D-glucose

CH2OH
6 CH2OH

6 CH2OH
5

H
4

OH

H
OH
3

H

O

H

H

1

2

OH

α-D-glucose

OH

5

H
4

OH

H

OH
3

H

O

OH

H

1

2

H

OH

β-D-glucose

These representations of the cyclic sugars are called Haworth projections.


Fructose Ring Structures
Fructose may form 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.


Monosaccharides
Some examples
of pyranose ring
structures for
hexose sugars.
The ring is not
actually planar
but exists in boat
and chair
conformers


Sugar Derivatives
CH2OH

CH2OH
H

O
H

OH

H

H
OH

OH
H

H

NH2

α-D-glucosamine

O
H
OH

H

H
O OH

OH
H

N

C

CH3

H

α-D-N-acetylglucosamine

An Amino sugar is a sugar in which an amino group
substitutes for a hydroxyl. An example is glucosamine.
The amino group may be converted to an amide, as in
N-acetylglucosamine.


Anomers of Glucose
6 CH2OH

6 CH2OH
5

H
4

OH

H
OH
3

H

O

H

H

1

2

OH

α-D-glucose

OH

5

H
4

OH

H
OH
3

H

O

OH

H

1

2

H

OH

β-D-glucose

Cyclization of glucose produces a new asymmetric center
at C1. The 2 stereoisomers are called anomers, α & β.
Haworth projections represent the cyclic sugars as having
essentially planar rings, with the OH at the anomeric C1:
 α (OH below the ring)
 β (OH above the ring).


Glycosidic Bonds
The anomeric hydroxyl groups of two sugars
can join together, splitting out water to form a
glycosidic bond.
Two gluocose molecules combine to form a
disaccharide known as maltose.

Disaccharides

•Double sugars
•Good source of energy
•Break down into simple sugars Sucrose (glucose + fructose)
Other disaccharides include: Lactose (glucose + galactose)
-- Sucrose, common table sugar, has a glycosidic bond
linking the anomeric hydroxyls of glucose & fructose.
-- Because the configuration at the anomeric C of glucose is
α (O points down from ring), the linkage is α(1→2).
The full name of sucrose is α-D-glucopyranosyl-(1→2)-β−
D-fructopyranose.)
-- Lactose, milk sugar, is composed of galactose
& glucose,
H H
with β(1→4) linkage from the anomeric OH of galactose.
Its
full name is β-D-galactopyranosyl-(1→ 4)-α-Dglucopyranose


Disaccharides
•Compare the structures of these three common
disaccharides

H H

•Sucrose is an A (1-4) link between D-Glucose and DFructose
•Lactose is

Polysaccharides
•3 or more sugars linked together
•Storage energy
•Complex sugars
Examples:
Starch- (plants) found in leaves, tubers…
Glycogen- (animals) found in the liver and muscles
Cellulose- (plants) make up cell walls

Starch


Cellulose
• Major building component of plant cell walls
• Long chain of glucose molecules; should be great source of
energy, but…
• Humans cannot digest cellulose since they lack the
necessary enzyme
• Endosymbiotic protist in cow guts DOES have the enzyme


Polysaccharides _Starches
CH2OH
O

H

H

OH

H

OH
H

OH

H

H

1

O

6CH OH
2
5
O

H

4 OH

H

3

H 1

H

H
O

CH2OH

CH2OH

CH2OH
O
H
OH

H

H

OH

H

H
O

O
H
OH

H

2

OH

H

OH

H

H
O

O
H
OH

H

H
OH

H

OH

amylose

• Plants store glucose as amylose or amylopectin. Both are
glucose polymers collectively called starch.
• Glucose storage in polymer form minimizes osmotic
effects.
 Amylose is a glucose polymer with α (1→4) linkages.
 The end of the polysaccharide with an anomeric C1 not
involved in a glycosidic bond is called the reducing end.


Polysaccharides _Starches
CH2OH
H

O
H
OH

H

OH
H

OH

H

H

1

O

6CH OH
2
5
O

H

4 OH

H

3

H 1

H

H
O

CH2OH

CH2OH

CH2OH
O
H

OH

H

H

OH

H

H
O

O
H
OH

H

2

OH

H

OH

H

H

O

O
H
OH

H

H
OH

H

amylose

• The Real difference between amylose starch and
cellulose is in the glycosidic link between successive
saccharide units

OH


Amylopectin
CH2OH

CH2OH
O

H

H
OH

H

H

OH

H
O

OH
CH2OH
H

H

OH
H

O
H
OH

H

H

OH

CH2OH
O

H
OH

H

OH

H

H
O

O
H
OH
H

H
OH

H

H
O

4

amylopectin

H
1
O
6 CH2
5
H
OH
3
H

CH2OH
O
H
2
OH

H

H
1
O

CH2OH
O

H
4 OH

H

H
OH

H

H
O

O
H
OH

H

H
OH

H

OH

 Amylopectin is a glucose polymer with mainly α(1→4)
linkages, but it also has branches formed by α (1→6) linkages.
Branches are generally longer than shown above.
• The branches produce a compact structure & provide multiple
chain ends at which enzymatic cleavage can occur.

Glycogen
CH2OH

CH2OH
O

H

H
OH

H

H

OH

H
O

OH
CH2OH
H

H

OH
H

O

H
OH

H

H

OH

CH2OH
O

H
OH

H

OH

H

H
O

O
H
OH
H

H

OH

H

H
O

4

glycogen

H
1
O
6 CH2
5
H
OH
3
H

CH2OH
O
H
2
OH

H

H

1
O

CH2OH
O

H
4 OH
H

H
OH

H

H
O

O
H
OH

H

H
OH

H

OH

• Glycogen, the glucose storage polymer in animals, is similar
in structure to amylopectin found in plants
• Glycogern has more α (1→6) branches.
• The highly branched structure permits rapid glucose release
from glycogen stores, e.g., in muscle during exercise.
•T he ability to rapidly mobilize glucose is more essential to
animals than to plants.


The End
.