STUDENT PRESENTATION

1. MOLECULES
S.ANGEL
M.Sc NEURO

2. WHAT IS A MOLCULE
• Two or more atoms unite together to form
a molecule. It maybe formed by the union
of similar or dissimilar atoms.
• E.g.: oxygen molecule o2 is formed by the
union of two oxygen atoms.

3. MOLECULAR INTERACTION
• The interaction between molecule to form
complex biological molecules are called
molecular interaction.
• They are the weak forces between ions or
atoms in the molecules.
• Important for the stability of
supermolecular structure.

4. MOLECULAR INTERACTION
• They are also known as secondary
chemical bonds.
• There is no transfer and sharing of
electrons between atoms during molecular
interaction.

5. IMPORTANT MOLECULAR
INTERACTION
• HYDROGEN BONDS
• VAN DER WAAL’S INTERACTION
• COLLOIDAL INTERACTION
• DIPOLE INTERACTION
• HYDROPHOBIC INTERACTION
• ANHYDRO INTERACTION

6. HYDROGEN BONDS
• The weak bond formed between an
electronegative atom of one molecule and
the electropositive hydrogen atom of
another molecule , due to an electrostatic
force is called hydrogen bond.
• It is also known as proton bond.

7. HYDROGEN BOND
• The length of the hydrogen bond is less
than 3A0 .
• The bond energy varies from 2 to 6
Kcal/mole for O-O covalent bond.
• Influence the structure and shape of the
macromolecule.
• Predominant in the living system.

8. HYDROGEN BONDS

9. HYDROGEN BOND
• In water- It is held together by the
hydrogen bonding. It has one oxygen and
two hydrogen atoms . The oxygen atom
forms hydrogen bonding with two
hydrogen atoms of different water
molecule.
• The hydrogen atoms forms hydrogen
bonding with oxygen atom of two different
water molecule. So one water molecule is
surrounded by 4 water molecule.

11. HYDROGEN BOND
In ice crystal, the H2O
molecule exist in
tetrahedrons. They are
interconnected by H-
bonds.

12. COLLOIDAL INTERACTION
• ELECTROSTATIC INTERACTION
1. They carry electric charges(+
ve and – ve). They attract or repel each
other.
• VAN DER WAAL’S FORCES
1. Interaction between two
dipoles.

13. DIPOLE INTERACTION
• The molecule having positive charge at
one end and negative charge at the other
end is called dipole.
• Dipoles are capable of moving in the
solution depending on the ionic strength
and the movement is called dipole
movement.

14. DIPOLE MOVEMENT OF
WATER MOLCULE

15. HYDROPHOBIC
INTERACTION
• Non polar molecules in an aqueous
solution tend to cluster together into a
complex molecule is known as
hydrophobic interaction.
• Important for enzyme- substrate binding,
antigen- antibody reaction etc.
• They repel water molecule and hence
does not dissolve in water.

16. HYDROPHOBIC INTEERACTON
IN PLASMA MEMBRANE

17. ANHYDRO BONDS
• They are the covalent bond formed between
two molecules by removal of water , by
getting an –OH from one molecule and a –H
from the other molecule.
• E.g. the sugar molecule connected by the
anhydro bonds. The anhydro bond connecting
a sugar molecule are called glycosidic bond.

18. • When two amino acids are connected by an
anhydro bond are called peptide bonds.
• They formed by the removal of –OH group
from the carboxyl group of one amino acid
and the –H atom from the amino group of
the other amino acid molecule.

19. VAN DER WAAL’S
INTERACTION
• The non-specific attraction between any
two atoms which keeps them at a distance
of 3-4A0 is called Van Der Waal’s
interaction.
• The distance between the Van Der Waals
interaction is called VAN DER WAAL’S
RADII.

20. VAN DER WAAL’S
INTERACTION
• Eg: The contact distance between
hydrogen and oxygen is 2.6A because the
Van Der Waal’s radius of hydrogen is 1.2A
and that of oxygen is 1.4A.
• The Van Der Waal’s energy between any
two atoms is 1kcal/mole.