Question

Insulin receptor is

• A. 'Thr' specific protein kinase
• B. 'Ser' specific protein kinase
• C. 'Tyr' specific protein kinase
• D. 'His' specific protein kinase

Hint:

The insulin receptor is a classic example of a Receptor Tyrosine Kinase (RTK). Its activation involves autophosphorylation of tyrosine residues, which differentiates it from serine/threonine kinases.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Cell-surface receptors transmit extracellular signals inside the cell. Receptor Tyrosine Kinases (RTKs) are a major class of receptors with intrinsic enzymatic activity.

Step 2: Detailed Explanation:
1. The insulin receptor is a transmembrane homodimer composed of two \(\alpha\) and two \(\beta\) subunits.
2. The intracellular domain of the \(\beta\) subunit contains intrinsic tyrosine kinase enzymatic activity.
3. Upon insulin binding to the extracellular \(\alpha\) subunits, the receptor undergoes conformational changes that trigger autophosphorylation of specific tyrosine residues on the intracellular \(\beta\) subunits.
4. This autophosphorylation recruits and activates downstream signaling proteins, such as Insulin Receptor Substrate-1 (IRS-1).

Step 3: Final Answer:
The insulin receptor functions as a tyrosine (Tyr) specific protein kinase.