This document summarizes the main types of biological bonding and interactions. It discusses that biological interactions fall into two categories: covalent and non-covalent interactions. Covalent interactions are strong bonds, while non-covalent interactions are weaker and include hydrogen bonds, ionic bonds, van der Waals forces, and hydrophobic interactions. Non-covalent interactions are further divided into ionic interactions, which are strong in dry conditions but dissolve in water, and hydrogen bonds, van der Waals forces, and hydrophobic interactions, which depend on factors like the polarity of the medium and presence of water molecules.

1. By Dr Naved Akbar
Biological Bonding/Interactions

2. Biological Bonding/Interactions
 Biological interactions (or bonds) in living systems fall under two categories
– covalent and non-covalent interactions.
 Covalent interactions are strong whereas non-covalent interactions are weak
interactions.
 The main types of weak interactions are hydrogen bonds, ionic bonds, van
der waals forces and hydrophobic interactions.
Covalent Interactions:
 Covalent interactions are very stable and the large energy charges are
associated with making and breaking of these interactions. E-g.- C – C,
C –O, C – N. (Peptide bond is amide type of covalent bond b/w CO-NH)
 Covalent bond is independent of the nature of the medium (Polar or Non-
Polar). It remains the same in both types of solutions either polar or non-
polar.
C – C
Polar
C – C
Non- Same bond strength

3.  Non-covalent interactions are weak interactions.
 These are two types: ionic interactions and non-ionic interactions.
Ionic Interactions (Salt bridge)
 These are very strong in anhydrous conditions. E.g.- Na+Cl-
 In aqueous condition it dissolve or dissociates.
 In anhydrous condition, these are stronger or equivalent than covalent
interactions.
 Water has a highest dielectric constant (80).
(Dielectric constant – A quantity measuring the ability of a substance to store
electric energy).
Non-covalent Interactions

4.  These are three types
I. Hydrogen bonds
 It is attractive bonding.
 It is dependent on the medium (polar or non-polar). High in polar medium.
 H-bonds are highly directional in that strength depends on the proper
alignment of the interacting atoms.
 For example : H – F, H – O, H – N.
Non-ionic Interactions

5.  It is the weakest type.
 Can be attractive or repulsive.
 Always intermolecular interaction (b/w two molecules).
 It is independent of the medium.
 Dipole – Dipole Dipole – Induced dipole
 Induce dipole – Induce dipole
Van Der Waals Forces/Interactions
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+
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+
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Attractive
Repulsiv
e
Lizard’s web

6.  It is always arise in the presence of H2O (water).
 It depends on the free water molecule number.
 If the free H2O molecules increases, hydrophobic interaction increases.
 The non-polar molecules gets aggregated in the presence of free water
molecules having interior of hydrophobic forces.
 They are responsible for the structure of membrane and the stability of
proteins.
Hydrophobic Interactions
Add
H20

7. THANK YOU