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Internal receptors are soluble proteins that bind signaling molecules inside cells, either in the cytoplasm or nucleus, to trigger a response, such as a change in gene expression.

Typically, the ligands that bind to internal receptors are hydrophobic, non-polar molecules that diffuse through the plasma membrane of the targeted cells, or are compounds that may be synthesized intracellularly.

Once a ligand binds, a conformational change is induced in the receptor, which allows it to bind with other molecules in the cell.

For example, when the hormone testosterone, or its enzymatically converted form dihydrotestosterone, DHT, binds to an androgen receptor in the cytoplasm, the ligand-bound complex then undergoes structural changes, allowing it to move into the nucleus, dimerize, and expose a DNA-binding site, a region on the receptor that recognizes specific nucleotide sequences of DNA.

In this case, the areas of binding are called hormone, or androgen-response elements, which modulate the activity of certain genes, either promoting or blocking the synthesis of mRNAs to mediate androgen-specific effects in cells.