Read the following statements and select the correct option. Statement A : Only steroid hormones are able to cross the cell membrane and act via intracellular receptors. Statement B : Steroid hormones stimulate regulatory genes present on the chromosomes and thus regulate gene expression

Options

A. Only statement A is incorrect
B. Only statement B is incorrect
C. Both statements are incorrect
D. Both statements are correct

Answer

To solve the question, we need to evaluate the two statements provided:

**Statement A:** "Only steroid hormones are able to cross the cell membrane and act via intracellular receptors."

1. **Understanding Cell Membrane Structure:** The cell membrane is primarily composed of a phospholipid bilayer, which allows certain types of molecules to pass through.

2. **Nature of Steroid Hormones:** Steroid hormones are lipophilic (fat-soluble) molecules. Because of their lipid nature, they can easily diffuse through the lipid bilayer of the cell membrane.

3. **Mechanism of Action:** Once inside the cell, steroid hormones bind to intracellular receptors, which can be located in the cytoplasm or nucleus. This binding leads to the formation of a hormone-receptor complex that can interact with DNA to regulate gene expression.

4. **Conclusion for Statement A:** Since steroid hormones can cross the cell membrane due to their lipid solubility, this statement is true. However, it is worth noting that some non-steroid hormones can also have intracellular effects, but they typically do so through secondary messengers rather than directly crossing the membrane.

**Statement B:** "Steroid hormones stimulate regulatory genes present on the chromosomes and thus regulate gene expression."

1. **Gene Regulation by Steroid Hormones:** After the steroid hormone binds to its receptor, the hormone-receptor complex translocates to the nucleus where it binds to specific DNA sequences (regulatory regions of genes).

2. **Effect on Gene Expression:** This binding can enhance or inhibit the transcription of specific genes, leading to changes in mRNA production and subsequent protein synthesis.

3. **Conclusion for Statement B:** This statement is also true as steroid hormones indeed stimulate regulatory genes and influence gene expression.

**Final Evaluation:**
Both statements A and B are correct. Therefore, the correct option is that both statements are true.

### Summary:
- **Statement A:** True
- **Statement B:** True
- **Final Answer:** Both statements are correct.