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Chemical basis of life
CHPTER ONE
Chemical structure of Organism's bodies
(Carbohydrates and lipids)
Body
Organelle
System
Cell
Organ
Tissue
Cells of the living organism consist of organic molecules and
inorganic molecules, and each of them consists of atoms.
Organic molecules:
They are large sized molecules so they are called biological
macromolecules as Carbohydrates, fat (lipids), proteins and nucleic
acids. Mainly they are containing carbon and hydrogen.
The Biological macromolecules are essential for life, also they are
called polymers.
It is formed by the union of small molecules (Monomers) through the
polymerization process.
The biological macromolecules are classified according to their
molecular structure and their function into four groups:
 They are includes sugars, Starch and fibers.
 Its general formula is (CH2O)n.
 It consists of carbon , hydrogen and oxygen in ratio 1 : 2 : 1
Importance of Carbohydrates:
1-Carbohydrates are considered the fast and basic resources for
obtaining the energy.
2- Carbohydrates are used for storing energy in living organisms’
bodies until they require it.
3- Carbohydrates are a basic component for some parts of the cell
such as cellulose in the root of plant cells.
Classification of carbohydrates:
 Carbohydrates are classified according to their molecular
structure into:
1)Simple sugars:
Its chemical structure may be monosaccharide (one sugar molecule)
as glucose or disaccharide as sucrose (two sugar molecules).
a) Monosaccharaides
* The most simple sugars, it consists of a series of carbon atoms
(3 – 6) .each of them is joined with oxygen and hydrogen atoms.
As glucose, fructose, galactose and ribose.
* They are easily soluble in water and it has low molecular weight
and sweet taste.
Role of monosaccharide in the processes of transferring energy inside
the cells of living organisms:
In the bodies of the living organisms, these monosaccharides as
glucose are oxidized inside the mitochondria of the cell, so energy is
released from the bonds of the food to store in the form of ATP.
b) Disaccharides
They are formed as a result of combination between two molecules of
monosaccharide
Examples : 1- Sucrose = Glucose + Fructose
2- Maltose = 2 Glucose
3- Lactose = Glucose + Galactose.
2- Complex sugars:
They are polysaccharides as starch, Cellulose and glycogen. It
consists of many glucose molecules joined together
 It has high molecular weight and low ability to dissolve in water
and tasteless.
Biological macromolecules consist of carbon, hydrogen and oxygen.
They are formed of a large group of heterogeneous compounds. They
include simple lipids as fats, oils and waxes and complex lipids as
phospholipids and steroids.
All lipids insoluble in water but they can dissolve in non polar solvents as
benzene and tetra carbon chloride (CCl4) .
Lipids are formed from the union of three fatty acids and one
glycerol molecule. Glycerol is an alcohol contains three hydroxyl
groups.
Importance of lipids:
1-Lipids as energy source:
Energy produced from lipids is greater than energy produced from
the same amount of carbohydrates.
The body starts to extract energy from lipids in case of absence of
carbohydrates.
2-Lipids and cell building:
Lipids forms about 5% of organic substance inside the cell, it has an
important role in the structure of cell membranes.
Lipids act as heat insulator under skin in man and animal, so animals
can keep their body temperature in very cold places.
Lipids act as protective cover for surfaces of many plants and
animals, and some of them act as hormones as in case of steroids.
Lipids are classified according to their chemical structure into two
major groups; they are simple and complex lipids.
A) Simple lipids:
They are formed as a result of reaction between fatty acids and
alcohols. they are subdivided according to the degree of saturation of
fatty acids and the kind of alcohol into: Oils, Fats and waxes.
1- Oils
They are liquid fats formed by the reaction of unsaturated fatty acids
with glycerol and called triglycerides. for example the liquid fats that
cover the feathers of water birds to prevent water penetration into
their bodies.
2- Fats
They are differing from oils as they are solid substances, they are
formed by the reaction of the saturated fatty acids with glycerol and
also they are called triglycerides.
3- Waxes
They are made by the reaction of fatty acids of high molecular weight
with monohydric alcohols, for example the waxes that cover the
desert plant leaves to reduce water loss during transpiration.
B) Complex lipids:
They contain Hydrogen, carbon and oxygen in their structure in
addition to phosphorus and sulphur as phospholipids that present in
the cell membrane of animal and plants.
Phospholipids are similar to fat molecules in the structure except for
the phosphate group (P O4) which replaced the third fatty acid as
follow :
c) Derivative lipids:
They are lipids derived from both simple and complex lipids by
hydrolysis such as cholesterol and some hormones.