Which of the hormone has 4 subunits and 2 units for tyrosine kinase receptor binding?
**Core Concept**
The question is testing the student's knowledge of hormone receptors, specifically the insulin receptor, which belongs to the family of receptor tyrosine kinases (RTKs). This family of receptors plays a crucial role in signal transduction, regulating various cellular processes such as growth, differentiation, and metabolism.
**Why the Correct Answer is Right**
The insulin receptor is a heterotetrameric complex consisting of two alpha subunits and two beta subunits. The beta subunits have intrinsic tyrosine kinase activity, which is essential for the receptor's signaling function. When insulin binds to the alpha subunits, it induces a conformational change that activates the tyrosine kinase activity of the beta subunits. This activation leads to the phosphorylation of various downstream substrates, initiating a cascade of signaling events that regulate glucose metabolism and other cellular processes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the hormone receptor with 4 subunits and 2 units for tyrosine kinase receptor binding. While some receptors may have 4 subunits, they are not all associated with tyrosine kinase activity.
**Option B:** This option is incorrect because the epidermal growth factor receptor (EGFR) is a single polypeptide chain with intrinsic tyrosine kinase activity, but it does not have 4 subunits.
**Option C:** This option is incorrect because the platelet-derived growth factor receptor (PDGFR) is a single polypeptide chain with intrinsic tyrosine kinase activity, but it does not have 4 subunits.
**Clinical Pearl / High-Yield Fact**
The insulin receptor is a key regulator of glucose metabolism, and dysregulation of the insulin signaling pathway is associated with various metabolic disorders, including type 2 diabetes and insulin resistance.
**Correct Answer: C. Insulin receptor.**