Thyroxine brings about effects on target cells by

Options

A. Altering gene expression
B. Activating adenlate cyclase
C. Activating guanylate cyclase
D. Activating G-protein

Answer

**Step-by-Step Solution:**

1. **Understanding Thyroxine**: Thyroxine is a hormone produced by the thyroid gland. It plays a crucial role in regulating metabolism, growth, and development in the body.

2. **Mechanism of Action**: Thyroxine exerts its effects primarily by interacting with specific receptors within target cells. These receptors are typically located in the nucleus of the cell.

3. **Binding to Nuclear Receptors**: When thyroxine enters a target cell, it binds to intracellular receptors, specifically nuclear receptors. This binding occurs on the nuclear membrane.

4. **Formation of Hormone-Receptor Complex**: The binding of thyroxine to its nuclear receptor forms a hormone-receptor complex. This complex is essential for the subsequent steps in gene regulation.

5. **Interaction with Chromatin**: The hormone-receptor complex then binds to chromatin, which is the material that makes up chromosomes. This interaction is critical for initiating gene regulation.

6. **Gene Regulation**: Once the hormone-receptor complex is bound to chromatin, it initiates the process of gene regulation. This involves the transcription of DNA into messenger RNA (mRNA).

7. **Protein Synthesis**: The mRNA produced from transcription is then translated into proteins. These proteins are responsible for carrying out the various functions regulated by thyroxine.

8. **Conclusion**: Therefore, thyroxine brings about effects on target cells by altering gene expression, which leads to changes in protein synthesis and ultimately affects the cell's function.

**Final Answer**: Thyroxine brings about effects on target cells by altering gene expression.

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