4 - Biological Molecules.docx

1. Biological Molecules
All Biological Molecules are Organic!
A biological or organic molecule is:
 Carbon (C) based
 Made from living matter.
All organisms are made up of organic molecules that contain
Carbon (C), Hydrogen (H) and Oxygen (O).
Organisms need organic molecules to:
 Provide energy for life processes (energy is obtained
from carbohydrates and lipids in food).
 Provide raw materials for tissue growth and repair
(proteins in food molecules contain these raw
materials).
This means that Carbohydrates, Fats and Proteins are all
Organic.
Understanding Hydrolysis and Condensation!
Carbon atoms bond strongly with each other, forming chains
or rings which are complex molecules.
What all are present in Organic Molecules?
Your Notes
The word organism is
said to have come from
the word “organic”.
The study of organic
and inorganic
molecules that make
living organisms is
called Biochemistry.
Key Definitions:
 Hydrolysis is the breakdown of large complex
molecules into small simple molecules by the
addition of water.
 Condensation is the process when small simple
molecules condense to build up large complex
molecules by the removal of water.

2. Carbohydrate Molecules
Carbohydrates are either:
 Complex (polysaccharides): insoluble in water,
stores of energy, formed from many
monosaccharides (examples include starch,
cellulose and glycogen).
 or Simple (monosaccharides): soluble in water
(dissolve in the cytoplasm of cells), main source of
energy in cells, can easily be transported by blood
(examples include glucose).
Monosaccharides
are formed by the
hydrolysis of
polysaccharides,
and polysaccharides
are formed by the
condensation of
monosaccharides.
Lipid/Fat Molecules
Lipids are broken down into:
 Fatty acids
 and Glycerol
Lipids are formed by the condensation
of 3 molecules of fatty acids and 1
molecule of glycerol.
The diagram of C, H
and O is shown on the
right-hand side.
Notice that water
(H2O) breaks down the fats.
Protein Molecules
Amino acids are the subunits that are put together in
different combinations to form chains called proteins.
 They are soluble which allows easy transport
because they are used in several reactions.
 Sequences of amino acids determine the shape of
a protein (examples are: keratin (present in skin
and hair) is long and thin and haemoglobin
(present in RBCs and can carry oxygen) is
biconcave shaped).
Amino acids build up proteins by condensation, and are
formed by the breakdown of proteins hydrolysis.
Your Notes
There is a semi-
complex form of
carbphydrates known
as disaccharides which
are not touched upon
in this unit.

3. Nucleic Acid Molecules
Nucleic Acids are present in
deoxyribonucleic acid (DNA) and
ribonucleic acid (RNA). The
subunits of these acids are known
as nucleotides. This means that
nucleic acids are chains of
nucleotides.
Each nucleotide is made up of a
sugar, phosphate and a
nitrogenous base. Each
nucleotide differs based on its
base.
There are 4 nucleotides, suggesting that there are 4 bases
(In all nucleic substances other than RNA):
 A – Adenine
 T – Thymine
 G – Guanine
 C – Cytosine
 U – Uracil (Replaces Thymine in RNA).
A-T are complimentary and G-C
are complementary (in RNA A-U
is complementary).
These combinations form
ladders in different
combinations of A-T, T-A, G-C
and C-G:
 The wall of these ladders are
made up of the sugar and
phosphates in each nucleotide.
 The rungs or the steps of the
ladder are made up of the
nitrogenous bases
The combinations of bases
repeat to form a DNA molecule.
The genome (all genes
that make up an
organism) pattern in
each organism is what
makes each organism
(plant, animal even
bacterium) different and
unique.
This ladder forms a
twisted shape called a
double helix when
nucleic chains are coiled
around one another.
Your Notes
DNA structure can be described
as:
 two strands coiled together
to form a double helix
 each strand contains
chemicals called bases
 cross-links between the
strands are formed by pairs
of bases
 the bases always pair up in
the same way: A with T, and
C with G

4. Water, An Important Solvent!
Water is important for all living organisms as many substances are able to dissolve in it (it is a
solvent). This makes it incredibly useful and essential for all life on Earth.
Water is important as a solvent in the following situations within organisms:
 Dissolved substances can be easily transported around organisms
 Digested food molecules are in the alimentary canal but need to be moved to cells all
over the body
 Toxic substances such as urea and substances in excess of requirements such as salts
can dissolve in water which makes them easy to remove from the body in urine
 Water is also an important part of the cytoplasm and plays a role in ensuring metabolic
reactions can happen as necessary in cells
Protein Shape! – Continued
There are thousands of different proteins in the human body and other organisms. Many of
these proteins are different shapes and the shape often has an important effect on the
function of the protein.
For example:
 Enzymes have an area in them known as the active site – this is important as this is the
place where another molecule fits into the enzyme in order for a reaction to take
place.
 If the shape of the active site does not match the shape of the molecule that fits into
it, the reaction will not take place.
 Antibodies are proteins produced by certain types of white blood cell to attach to
antigens on the surface of pathogens.
 The shape of the antibody must match the shape of the antigen so that it can attach to
it and signal it for destruction.
The different sequences of amino acids cause the polypeptide chains to fold in different
ways and this gives rise to the different shapes of proteins. In this way every protein has a
unique 3D shape that enables it to carry out its function.