Internal receptors are soluble proteins that bind signaling molecules inside cells, either in the cytoplasm or nucleus, to trigger responses, such as changes 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. For example, the hormone testosterone or its enzymatically processed form dihydrotestosterone, or DHT, binds to an androgen receptor in the cytoplasm. The receptor-ligand complexes move into the nucleus and dimerize. The DNA-binding site of the receptor recognizes and binds to specific nucleotide sequences called hormone or androgen-response elements. The binding modulates the activity of specific genes, either promoting or blocking the synthesis of mRNAs that mediate androgen-specific effects in cells.