Final answer:
Internal receptors are proteins located in the cell cytoplasm that bind to hydrophobic ligands, leading to gene expression by initiating transcription directly in the nucleus.
Step-by-step explanation:
Internal receptors, also known as intracellular or cytoplasmic receptors, are located within the cytoplasm of a cell and play a critical role in the process of gene expression.
These receptors bind to hydrophobic ligand molecules that easily cross the plasma membrane due to their lipophilic nature, such as steroid hormones and thyroid hormones.
Once a hydrophobic ligand enters the cell and interacts with an internal receptor, this triggers a conformational change within the receptor, exposing a DNA-binding domain.
The ligand-receptor complex then translocates to the nucleus, where it binds to specific regions on the DNA, initiating transcription.
Transcription is the process through which the information coded in DNA is transcribed into messenger RNA (mRNA), which then leaves the nucleus and guides the synthesis of proteins in the cytoplasm via ribosomes, a process called translation.
This mechanism by which internal receptors directly influence gene expression without the need for further signaling or secondary messengers is pivotal for the regulation of various physiological processes.