The iodine derivative of amino acid tyrosine brings about effects on target cells by

Options

A. Altering gene expression
B. Activating secondary messengers
C. Activating membrane - bound receptors
D. More than one option is correct

Answer

To solve the question regarding how the iodine derivative of the amino acid tyrosine affects target cells, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Iodine Derivative of Tyrosine**:
- The iodine derivatives of the amino acid tyrosine are the thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3).

2. **Understand the Mechanism of Action of Thyroid Hormones**:
- Thyroid hormones, despite being lipid-soluble, act via intracellular receptors. This is an important distinction because it sets them apart from many other hormones.

3. **Determine How Thyroid Hormones Affect Target Cells**:
- Thyroid hormones can enter target cells and bind to intracellular receptors. Once bound, they can directly influence gene expression by altering the transcription of specific genes.

4. **Evaluate the Options Provided**:
- **Altering Gene Expression**: This is correct, as thyroid hormones can change the expression of genes in target cells.
- **Activating Secondary Messengers**: This is incorrect for thyroid hormones, as they do not primarily act through secondary messengers.
- **Activating Membrane Bound Receptors**: This is also incorrect for thyroid hormones, as they do not primarily use membrane-bound receptors.
- **More than One Option is Correct**: This is incorrect since only one option (altering gene expression) is valid.

5. **Conclude the Answer**:
- The correct answer is that the iodine derivative of the amino acid tyrosine (thyroid hormones) brings about effects on target cells by **altering gene expression**.

### Final Answer:
The iodine derivative of amino acid tyrosine brings about effects on target cells by **altering gene expression**.

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