Carbohydrates are the sugars, starches and fibers found in fruits, grains, vegetables and milk products. Though often maligned in trendy diets, carbohydrates — one of the basic food groups — are important to a healthy life
2. Carbohydrates – polyhydroxyaldehydes or polyhydroxy-
ketones of formula (CH2O)n, or compounds that can be
hydrolyzed to them. (aka sugars or saccharides)
Monosaccharides – carbohydrates that cannot be hydrolyzed
to simpler carbohydrates; eg. Glucose or fructose.
Disaccharides – carbohydrates that can be hydrolyzed into
two monosaccharide units; eg. Sucrose, which is hydrolyzed
into glucose and fructose.
Oligosaccharides – carbohydrates that can be hydrolyzed into
a few monosaccharide units.
Polysaccharides – carbohydrates that are are polymeric
sugars; eg Starch or cellulose.
3. Aldose – polyhydroxyaldehyde, eg glucose
Ketose – polyhydroxyketone, eg fructose
Triose, tetrose, pentose, hexose, etc. – carbohydrates that
contain three, four, five, six, etc. carbons per molecule
(usually five or six); eg. Aldohexose, ketopentose, etc.
4. Reducing sugar – a carbohydrate that is oxidized by Tollen’s,
Fehling’s or Benedict’s solution.
Tollen’s: Ag+
Ag (silver mirror)
Fehling’s or Benedict’s: Cu3+
(blue) Cu2+
(red ppt)
These are reactions of aldehydes and alpha-hydroxyketones.
All monosaccharides (both aldoses and ketoses) and most*
disaccharides are reducing sugars.
*
Sucrose (table sugar), a disaccharide, is not a reducing sugar.
11. Ruff degradation – a series of reactions that removes the
reducing carbon ( C=O ) from a sugar and decreases the
number of chiral centers by one; used to relate configuration.
CHO
H OH
CH2OH
H OH
CO2H
H OH
CH2OH
H OH
Br2
H2O
CO2
H OH
CH2OH
H OH
Ca2+
H2O2
Fe3
+
CHO
CH2OH
H OH
D-(+)-glyceraldehyde
12. Kiliani-Fischer synthesis. A series of reactions that extends the
carbon chain in a carbohydrate by one carbon and one chiral
center.
CHO
H OH
CH2OH
HCN
C
H OH
CH2OH
H OH
C
HO H
CH2OH
H OH+
N N
H+,H2O
COOH
H OH
CH2OH
H OH
COOH
HO H
CH2OH
H OH
diastereomers
separable
C
H OH
H2C
H OH
O
O
lactone
Na(Hg)
CHO
H OH
CH2OH
H OH
-H2O
13. Epimers – stereoisomers that differ only in configuration about
one chiral center.
CHO
OHH
HHO
OHH
OHH
CH2OH
D-glucose
CHO
HHO
HHO
OHH
OHH
CH2OH
D-mannose
epimers
14. CHO
OHH
HHO
OHH
OHH
CH2OH
(+)-glucose
Exists only in solution. There are two
solids:
α-glucose m 146o
[α] = +112.2
β-glucose m 150o
[α] = +17.5
In water each mutarotates to an
equilibrium with [α] = +52.7
(63.6% β / 36.4% α)
16. R
C
H
O
+ R'OH R C H
OH
OR'
R C H
OR'
OR'
hemiacetal
geminal
ether/alcohol
reducing!
acetal
geminal
diether
non-reducing!
Addition of alcohols to aldehydes/ketones:
25. O
H
HO
H
HO
H
OHH
H
OH
glucose alpha C-1
to beta C1 fructose
O
HO
H
H
HO
H
H
OHH
OH
O
H
O
H
HO
H
H
OHH
OH
OH galactose beta C-1
to C-4 glucose
reducing sugar(+)-lactose
O
O
CH2OH
CH2OH
H
H
OH
HO
H
(+)-sucrose
acetal
non-reducing
26. Polysaccharides
starch
cellulose
Starch 20% amylose (water soluble)
80% amylopectin (water insoluble)
amylose + H2O (+)-maltose
(+)-maltose + H2O (+)-glucose
starch is a poly glucose (alpha-glucoside to C-4)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
28. Cellulose is a polyglucose with a beta-linkage:
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
29. Biological significance of carbohydrates in living organisms is as
follows:
Carbohydrates are energy stores of animals and plants.
Carbohydrates are immediate source of energy while lipids are long-term source
of energy.
Glucose is a free sugar which circulates in blood and is an important substance
for normal cell functioning.
Regulation of glucose metabolism is vital for survival. Carbohydrates make up
most of the plant of about 60-80% of its dry mass.
In plants they are used as energy source and for storage in the form of starch.
Cellulose which is a polysaccharide is an important structural component in the
cell wall of plants.
Sucrose, a disaccharide is a product of photosynthesis and is transported
internally.
Carbohydrates are an important component of diet in animals.
Carbohydrates are main source of energy and are essential to all animal life.
Carbohydrates act as fuel to physical body parts on daily basis.
30. Within the body carbohydrates
have six major functions:
They provide energy and regulate
blood glucose.
Help in breakdown of fatty acids
and prevents ketosis.
Aid in biological recognition
processes.
They minimize the use of proteins
for energy.
They also act as flavor and
sweeteners.