Which acts on nuclear receptors
**Core Concept**
The question is testing the understanding of **steroid hormones** and their mechanism of action, specifically how they interact with **nuclear receptors** to influence gene expression. This is a fundamental concept in **endocrinology** and **molecular biology**.
**Why the Correct Answer is Right**
Steroid hormones, such as **estrogen** and **cortisol**, can diffuse through the cell membrane and act on **nuclear receptors**. These receptors are ligand-activated transcription factors that, upon binding with their respective steroid hormones, translocate to the nucleus and regulate the transcription of target genes. This process involves the binding of the hormone-receptor complex to specific **DNA sequences**, known as hormone response elements, which are located in the promoter regions of target genes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the primary mechanism of action for steroid hormones.
**Option B:** Similarly, this option is incorrect as it does not correctly identify the site of action for steroid hormones.
**Option C:** This option is also incorrect because it misrepresents how steroid hormones function at the molecular level.
**Clinical Pearl / High-Yield Fact**
It's crucial to remember that **steroid hormones** have a broad range of effects on the body, from regulating metabolism and immune response to influencing growth and development. Understanding their mechanism of action is key to appreciating their role in both health and disease.
**Correct Answer:** D. Steroid Hormones.