This document summarizes the concepts of agonists and antagonists in receptor activation and inhibition. It defines agonists as ligands that enhance receptor activity and antagonists as those that oppose agonist action and block receptor activation. The document compares the properties and types of agonists, including full, partial, and inverse agonists, and antagonists, including competitive, non-competitive, and irreversible antagonists. It discusses how agonists and antagonists regulate signaling pathways through their effects on receptor activation and inhibition.

1. Concept of agonists and antagonists in
receptor activation and inhibition and
significance in regulation of signaling.
BY – RAHUL KUMAR
M.Sc. LIFE SCIENCE
3RD SEMESTER
CUG/2014/1073

2. Objective:
 Ligand & its types
 Agonist & Antagonist
 Properties & Types of Agonist
 Properties & Types of Antagonist
 Significance in regulation of signaling

3. Classification of ligands:
• Ligands are classified by effect upon binding to the receptor.
LIGANDS
Agonist
Antagonist

4. Comparison between agonist & antagonist:
Agonist
• Derived from Latin word –
contender.
• Aids in the enhancement of an
action.
Antagonist
• Derived from Latin & Greek
words – competitor or
opponent.
• Opposes the action of agonist
and block the reception.

5. Properties of agonist:
 Acute Signaling
 Desensitization
 Sequestration
 Resensitization

6.  Receptors can be activated either by endogenous or
exogenous , leads to change in the biological response.
 Types of agonist-
a) Full agonist
b) Partial agonist
c) Inverse agonist

7. Full agonist – The ligands that increase the activity of the receptors &
produce the maximal response .
Ex.- Morphine ,mimics the action of endorphins at
opioid receptors.
Partial agonist – These ligands partially increase the activity of the
receptors but do not produce the maximal
response like full agonist even when present in excess
amount.
Ex.- Buspirone , is an anxiolytic drugs , used to treat an
anxiety disorder.

8. Inverse agonist – The ligands which decrease the activity of
an active receptors to their inactive state.
Ex.- Flumazenil drugs acts as a inverse agonist for the
GABA receptor & produce anxiogenic effect.

9. Properties of Antagonist :
 Site selectivity.
 Structural conformation – mimics with the natural ligand.
 Reduces the response.
 Effect may be temporary or permanent.

10. Competitive
Types of antagonist-
Reversible
Irreversible
Non-competitive

11.  Competitive antagonists – The antagonist competes with
the agonist for the orthosteric sites for binding to
the same receptor .
- The effect of the antagonist can be overcome by
increasing the concentration of the agonist.
Ex.- IL-1RA protein competes with IL-1 for binding to
the cell surface interleukin-1 receptor.

12.  Non-competitive antagonists : The antagonist binds at a
different site other than orthosteric site on the receptor.
- The effect of the antagonist cannot be overcome by increasing
the concentration of agonist.
Ex.- Binding of cyclothiazide with mGLUR1 receptor.

13.  Irreversible antagonists:
May or may not competes with the agonist for orthosteric sites for binding to
the receptor.
- Forms covalent bond to the site.
Ex.- Aspirin.

14. Significance of regulation in signaling:

16. REFERENCES -
The cell (5th Edition) Cooper & Hausman
Lehninger principle of biochemistry (5th Edition)
Principles & Techniques of Biochemistry & Molecular biology (7th Edition) by
Kleith Wilson & John Walker
Handbook of cell signaling Vol.1 (2nd Edition)

17. THANK YOU