Lipid-soluble hormones usually bind to __ receptors.
A extracellular
B intracellular
C transmembrane
D G protein coupled
The correct answer and explanation is:
The correct answer is: B intracellular
Explanation:
Lipid-soluble hormones, such as steroid hormones (e.g., cortisol, estrogen, testosterone) and thyroid hormones, are able to pass through the lipid bilayer of the cell membrane because they are nonpolar and hydrophobic. This characteristic allows them to easily diffuse across the cell membrane and enter the cytoplasm of target cells.
Once inside the cell, these hormones bind to intracellular receptors located either in the cytoplasm or directly in the nucleus. These receptors are typically proteins that function as transcription factors. When a lipid-soluble hormone binds to its intracellular receptor, the hormone-receptor complex undergoes a conformational change that enables it to move into the nucleus (if it was not already there). Inside the nucleus, the complex binds to specific DNA sequences called hormone response elements (HREs), which regulate the transcription of target genes.
The activation or repression of gene transcription ultimately leads to changes in protein synthesis that modify cellular function. Because this process involves changes in gene expression, the effects of lipid-soluble hormones tend to be slower but more sustained compared to water-soluble hormones.
Why not the other options?
- A. Extracellular receptors: These receptors are found on the outside surface of the cell membrane and are typically for water-soluble hormones (like peptide hormones) that cannot cross the lipid membrane.
- C. Transmembrane receptors: These span the membrane and bind extracellular ligands but are mostly for water-soluble hormones and initiate signaling cascades inside the cell.
- D. G protein coupled receptors (GPCRs): These are a type of transmembrane receptor that bind extracellular hormones or ligands and trigger second messenger systems inside the cell. They are not the typical receptors for lipid-soluble hormones.
Summary
Lipid-soluble hormones bind to intracellular receptors because they can cross the cell membrane and directly influence gene expression by interacting with DNA inside the cell nucleus, resulting in regulation of protein synthesis and long-lasting cellular effects.