Drugs exert effects by

Drugs exert effects by

• A. Creating new responses
• B. Binding irreversibly to DNA
• C. Altering expression of genes without receptor mediation
• D. Activating, terminating, or modifying preexisting responses

Answer: (D)

Drugs work by modulating pathways that the body already uses. They interact with targets such as receptors, enzymes, ion channels, or transporters to change how normal signals are produced or terminated. This means they can activate a receptor to trigger a natural response, stop or dampen signaling to end a response, or tweak the strength or timing of an existing response through mechanisms like allosteric modulation or partial agonism. In short, the effect comes from altering preexisting physiological processes rather than creating entirely new ones. For example, an agonist turns up a natural signaling pathway, an antagonist blocks it to prevent the normal signal, and a positive allosteric modulator enhances the natural effect of a neurotransmitter. Other ideas—like producing new, unexplained responses or changing gene expression directly without mediator signals—don’t describe how most drugs exert their effects.

Drugs work by modulating pathways that the body already uses. They interact with targets such as receptors, enzymes, ion channels, or transporters to change how normal signals are produced or terminated. This means they can activate a receptor to trigger a natural response, stop or dampen signaling to end a response, or tweak the strength or timing of an existing response through mechanisms like allosteric modulation or partial agonism. In short, the effect comes from altering preexisting physiological processes rather than creating entirely new ones. For example, an agonist turns up a natural signaling pathway, an antagonist blocks it to prevent the normal signal, and a positive allosteric modulator enhances the natural effect of a neurotransmitter. Other ideas—like producing new, unexplained responses or changing gene expression directly without mediator signals—don’t describe how most drugs exert their effects.