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→Agonists
An agonist can be defined as '''a drug that binds to a target molecule and results in activation of the receptor and thus a tissue response'''.
An agonist can be defined as '''a drug that binds to a target molecule and results in activation of the receptor and thus a tissue response'''.
* An agonist forms a complex with the receptor. This complex is '''dynamic''' as the agonist will continously dissociate and associate with the receptor. The agonist will continue to do this and thus producing a response, until the concentration of the agonist is reduced to a level at which no tissue response occurs.
* An agonist forms a complex with the receptor. This complex is '''dynamic''' as the agonist will continously associate and dissociate with the receptor. The agonist will continue to do this and thus produce a response, until the concentration of the agonist is reduced to a level at which binding no longer occurs.
* The rate of complex fromation is dependent on two factors: '''agonist concentration''' and the '''number of free receptors'''.
* The rate of complex formation is dependent on two factors: '''agonist concentration''' and the '''number of free receptors'''.
* The '''affinty''' of a drug to a receptor varies and can be compared using the '''equilinbrum constant or K<sub>A</sub>'''.
* The '''affinity''' of a drug to a receptor varies and can be compared using the '''equilibrium constant or K<sub>A</sub>'''.
This can be defined as the concentration of a drug which results in 50% of receptors being bound in equilibrium or when '''K<sub>1</sub>=K<sub>-1</sub>'''.
This can be defined as the concentration of a drug which results in 50% of receptors being bound in equilibrium or when '''K<sub>1</sub>=K<sub>-1</sub>'''.
<big>'''Drug + Number of Free Receptors = Drug-Receptor Complexes'''</big>
<big>'''Drug + Number of Free Receptors = Drug-Receptor Complexes'''</big>
Where '''K<sub>1</sub>''' is the rate constant in a forward direction
Where '''K<sub>1</sub>''' is the rate constant in a forward direction (association rate constant)
and '''K<sub>-1</sub>''' is the rate constant in a backward direction
and '''K<sub>-1</sub>''' is the rate constant in a backward direction (dissociation rate constant)
Therefore a drug that has a higher affinity to a receptor has a lower '''K<sub>A</sub>''' value.
Therefore a drug that has a higher affinity to a receptor has a lower '''K<sub>A</sub>''' value.
* By an intracellular second messenger system
* By an intracellular second messenger system
* By DNA transcription
* By DNA transcription
==Antagonists==
==Antagonists==