Final answer:
Hydrophobic ligands utilize intracellular receptors to transmit signals inside the cell, directly influencing gene expression by interacting with DNA within the nucleus.
Step-by-step explanation:
The correct is Option 1:
Intracellular receptors (cytoplasmic receptors). Hydrophobic ligands, such as steroids, can cross the cellular membrane due to their ability to dissolve in the lipid bilayer. Once inside the cell, these ligands bind to intracellular receptors. These intracellular receptors are located within the cytoplasm and, upon binding to the ligand, they often translocate to the nucleus where they may directly influence gene expression by interacting with DNA. These receptors interact directly with cellular DNA and initiate transcription and translation processes. On the other hand, water-soluble hydrophilic ligands bind to cell-surface receptors that span the plasma membrane and perform signal transduction to transmit the signal to the inside of the cell.
Unlike hydrophobic ligands, hydrophilic ligands cannot easily cross the cell membrane. These molecules instead rely on cell-surface receptors to transmit signals into the cell. These receptors include ion channel-linked receptors, G-protein-coupled receptors (GPCRs), and enzyme-linked receptors, which are found on the exterior of the cell and initiate a signaling cascade upon ligand binding that ultimately leads to cellular responses.