Final answer:
Chemicals that bind to receptors but do not activate them are called antagonists. These chemicals can block the biological effects that would occur if the receptor were activated. In the scenario provided, the molecule added to the cells may be acting as an antagonist to turn off gene transcription.
Step-by-step explanation:
Chemicals that bind to but do not activate receptors are known as antagonists. Antagonists bind to receptors and prevent them from being activated by other ligands. This action can block the effect that would normally occur if the receptor were activated by an agonist, which is a type of ligand that binds to receptors and induces a biological response. In the given scenario, the small, water-soluble molecule being added to the dish of cells may be acting as an antagonist, thereby turning off transcription of a gene by blocking receptor activation.
Two common types of receptors that ligands can bind to are internal receptors and cell-surface receptors. Internal receptors typically interact with hydrophobic (water-insoluble) ligands that can permeate the cell membrane, while cell surface receptors bind to hydrophilic (water-soluble) ligands that cannot cross the cell membrane directly. Depending on the receptor type and the ligand, the resulting action can vary, leading to different cellular responses.