226 Steroid Hormones Regulate Gene Transcription
Let’s look at the direct action of steroid hormones. Here we have a steroid hormone. Because it’s a lipid, it gets inside the cell. Let’s look at what happens again. Here it goes: it gets in the cell, it binds to a protein, a receptor, and we know that that receptor dissociates from another protein component. So it’s a it’s actually a protein with two parts. One part, when it comes off, frees up the other parts, now still attached to the steroid hormone, to cross the nuclear envelope, get into the cell and bind to double helical DNA at DNA sequences specifically recognized by the hormone-receptor complex. So the steroid hormone receptor sits there. Let’s look at it one more time. It sits there just in waiting, either in the cytoplasm or sometimes they’re actually in the nucleus. This one is in the cytoplasm, gets into the nucleus, bound to the hormone. It can be transported into the nucleus and bind to DNA. And if you’re going to turn genes on, you better be able to bind to the DNA somewhere near the gene. And so we’re assuming that this is what’s happened here. That induces in this case, the transcription of a message which of course, gets out into the cytoplasm, associates with ribosomes which then translate the message into a protein that was not being made before. Steroid hormone receptors are in fact transcription factors.