## Core Concept
The question tests knowledge of hormone receptors, specifically their structure and mechanism of action. Hormone receptors can be classified based on their location and signaling mechanism, including tyrosine kinase receptors. These receptors typically have a specific subunit structure that facilitates their function.

## Why the Correct Answer is Right
The correct answer, **Insulin receptor**, is a type of receptor tyrosine kinase. It has a structure consisting of four subunits: two alpha subunits and two beta subunits. The alpha subunits are located outside the cell and bind insulin, while the beta subunits span the cell membrane and have tyrosine kinase activity. When insulin binds to the alpha subunits, it triggers a conformational change that activates the tyrosine kinase activity of the beta subunits, leading to the phosphorylation of tyrosine residues on target proteins.

## Why Each Wrong Option is Incorrect
- **Option A:** The growth hormone receptor is a single transmembrane domain receptor that activates associated tyrosine kinases upon ligand binding but does not have 4 subunits.
- **Option B:** The glucagon receptor is a G protein-coupled receptor (GPCR) and does not have a structure with 4 subunits or directly activate tyrosine kinase for its primary signaling mechanism.
- **Option D:** The TSH (Thyroid-Stimulating Hormone) receptor is also a GPCR and activates adenylate cyclase via G proteins, not through a tyrosine kinase receptor mechanism with 4 subunits.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the **insulin receptor** and **IGF-1 receptor** are similar in structure and function, both being receptor tyrosine kinases. This similarity is crucial for understanding the mechanism of action of insulin and insulin-like growth factors and their roles in glucose metabolism and cell growth.

## Correct Answer: . Insulin receptor