Intracellular Receptors Regulate Gene Expression by Activating Target Genes
- Some signaling molecules, such as steroid hormones, are hydrophobic and can pass through the plasma membrane of a cell.
- These molecules bind to intracellular receptors, which are typically located in the cytoplasm or nucleus.
- Upon binding, these receptors become activated and directly influence gene expression by interacting with specific DNA sequences, leading to the transcription of certain genes.
- Consider a conductor leading an orchestra.
- The conductor doesn’t play an instrument but guides the musicians to create a symphony.
- Similarly, intracellular receptors guide cells by activating specific genes, ensuring the right proteins are produced at the right time.
Intracellular receptors are like conductors, directing cellular activities by activating specific genes.
How Do Intracellular Receptors Work?
NoteIntracellular Receptors Activate Gene Expression by Forming Hormone-Receptor Complexes
Hormone Entry
- Steroid hormones, such as oestradiol, progesterone, and testosterone, are hydrophobic.
- This allows them to diffuse through the plasma membrane and enter the cell.
Binding to Receptor
- Once inside, the hormone binds to a specific intracellular receptor in the cytoplasm or nucleus.
- This binding activates the receptor, changing its shape to expose a DNA-binding domain.
Formation of Hormone-Receptor Complex
- The activated receptor and hormone form a hormone-receptor complex.
- This complex acts as a transcription factor, a molecule that can bind to DNA and influence gene expression.
DNA Binding and Gene Activation
- The hormone-receptor complex moves into the nucleus (if it isn’t already there) and binds to specific DNA sequences called hormone response elements (HREs).
- Binding to HREs initiates or enhances the transcription of target genes, leading to the production of specific proteins that carry out the hormone’s effects.
Steroid hormones can directly influence gene expression because they can cross the cell membrane and interact with intracellular receptors.
Examples of Steroid Hormones and Their Effects
1. Oestradiol
Oestradiol is a key hormone in the regulation of the menstrual cycle and reproductive processes.
- Target Cells: Oestradiol acts on cells in the ovary, uterus, and brain.
- Mechanism: In the hypothalamus, oestradiol binds to its receptor, forming a complex that enters the nucleus and enhances the transcription of the gonadotropin-releasing hormone (GnRH) gene.
