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Carbohydrates (CHO): are aldehyde or ketone group with multiple
hydroxyl groups having an empirical formula of (CH2O)n .
General biological role:
CHO make up most of plants tissues at a less extent, the animal tissues.
As energy stores: starch in plants and glycogen in animals are major
polysaccharides that are mobilized to give glucose which is the prime fuel
for generation of energy.
ATP is a phosphorylated sugar derivatives and universal for free energy.
Ribose and de oxy ribose sugars form part of the structural framework of
DNA and RNA, these sugars rings have conformation flexibility which is
important in the storage and expression of the genetic information.
Polysaccharides are structural element in the cell wall of bacteria and plants.
cellulose is the main component of plants cell wall.
1- Monosaccharide: a single sugar unit having a carbonyl group (either
aldehyde at C1 or keton at C2) .
D- glyceraldehyde
Di hydroxyl acetone (DHA)
4C sugar = tetrose
(either aldose or ketose)
5C sugar= pentose
6C sugar= hexose
7C sugar= heptose
Properties of monosaccharide:
1- White, solids, soluble in water, insoluble in non polar solvents.
2- All monosaccharide (having free aldehyde or keton group) .
3- All monosaccharide (except DHA) have one or more a symmetric carbon
atom (atom bound to 4 different groups) ( carbon atom having double or
triple bonds excluded from this category).
To determine whether the isomer is D or L we must look for the orientation
of (OH) group of the carbon atom farther from the carbonyl group and near
the CH2OH group, if to the right the isomer is D, if to the left the isomer is
Since all monosaccharide (except DHA) have one or more a symmetric
carbon. They are optically active and tend to rotate the plane of polarized
light either to the right (d or +) called dextrorotatory or to the left ( l or —)
called levorotatory.
Note: it is important note that there is no relation between D and d or L and
l. a sugar may have D form but rotates the plane of polarized light to the
right or left.
D (+) glucose
D (—) glucose
Sugar derivatives and biological importance:
Glycosides: compounds formed by the condensation of a monosaccharide
with the (OH) group of another monosaccharide (forming disaccharides) or
with the (OH) group of a non monosaccharide unit and this is called a glycan
1-Vanillin D- glucoside (glucovanillin or vallinoside): sourse of vanilla
2- Digoxin and Digitoxin
Stimulator for cardiac muscle contraction
Onset 15-30 min
longer acting
Half life 32-40 hr.
half life 4-6 days (preferred to use).
Deoxy and amino sugars
Deoxy sugars are sugar in which (OH) group has been replaced by hydrogen
- Amino sugars: have —NH2 group replacing (OH) group (usually at C2).
D-glucosamine (chitosamine)
A constituent of mucopolysaccharides and mucoproteins such as hyaluronic
acid, heparin and blood group substances , (heparin): is antithrombic agent.
galactos amine (chondrosamine)
A constituent of chondroitin (found in cornea, cartilage, skin, adult bones,
tendons, and heart valve).
Several antibiotics (erythromycin and carbomycin) contain amino sugars.
Erythromycin contain a di methyl amino sugar.
Carbomycin contain 3- amino D- ribose.
Streptomycin is another amino sugar antibiotic.
Ascorbic acid (Vit. C) is a sugar acid, a very stable compound and undergoes
oxidation to dehydroascorbic acid. Prolonged lack of Vit. C causes scurvy
and decreased resistance to disease.
Sugar phosphate: key intermediate in the process of glycolysis (break
down of glucose to give CO2, H2O, and energy ATP).