Final answer:
Cortisol, a steroid hormone, diffuses through cellular membranes and binds to intracellular receptors in the cytoplasm or nucleus, affecting gene expression. Its fat-soluble nature allows this direct interaction, distinguishing it from hormones that bind to surface receptors and are endocytosed, like insulin.
Step-by-step explanation:
Intracellular Receptor Binding
Cortisol is a hormone known for its role in the body's stress response and is part of a group of hormones referred to as steroid hormones. Steroid hormones are lipid-derived and can easily diffuse through the lipid bilayer of the plasma membrane of target cells due to their fat-soluble properties. Once inside the target cell, cortisol binds to an intracellular receptor that is either located in the cytoplasm or in the nucleus. This binding triggers a cascade of events where the hormone-receptor complex moves into the nucleus and interacts directly with the DNA, affecting gene expression and eliciting a specific response within the cell.
The distinct mechanism of cortisol involves its ability to pass through cell membranes and bind to these intracellular receptors, contrasting with hormones like insulin, which bind to cell-surface receptors and are then internalized through endocytosis. Over time, if there are elevated levels of a hormone like cortisol, feedback mechanisms may trigger a reduction in the number of receptors to maintain homeostasis, which is known as receptor down-regulation.
In summary, cortisol's chemical composition determines that it will bind to intracellular hormone receptors, following a different signaling pathway compared to hormones that bind to cell-surface receptors such as insulin.