Mechanism of action of Insulin occurs through?

NIA - 29 January 2023

Biochemistry & Nutrition

Easy

Appeared in: NIA - 29 January 2023

Explanation

Insulin binds to a specific receptor on the cell surface known as a receptor tyrosine kinase, which is a type of enzyme-linked receptor.
This binding activates the receptor's intrinsic tyrosine kinase enzyme activity, causing it to phosphorylate itself (autophosphorylation).
The activated receptor then phosphorylates and activates other intracellular enzymes, such as Insulin Receptor Substrates (IRS).
This initiates a downstream signaling cascade that orchestrates insulin's metabolic effects, making 'activation of intracellular enzymes' the primary mechanism.

Option A: This is a downstream effect, not the primary mechanism. The activation of intracellular enzymes leads to the translocation of GLUT4 transporters to the cell membrane, which then changes the membrane's permeability to glucose.
Option C: This is the primary mechanism for steroid hormones (e.g., cortisol, estrogen) and thyroid hormones. These hormones cross the cell membrane and bind to intracellular receptors that directly regulate gene transcription.
Option D: This mechanism is characteristic of G-protein coupled receptors (GPCRs), which use small, non-protein molecules like cAMP, IP₃, or Ca²⁺ as messengers. Glucagon and epinephrine work this way. Insulin uses an enzyme-linked receptor, which is a different class.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Insulin Signal Transduction Pathway as background academic context rather than a clinical decision trigger.
Understanding insulin's mechanism is fundamental to managing diabetes mellitus. Insulin resistance, the hallmark of Type 2 diabetes, involves defects in this signaling pathway, leading to reduced glucose uptake by cells.
Many pharmacologic agents for diabetes are designed to improve insulin sensitivity or bypass defects in this pathway.
Insulin administration in a clinical setting, particularly intravenous insulin, can cause rapid shifts in potassium into cells (along with glucose), leading to hypokalemia. This is a direct consequence of the signaling cascade stimulating the Na⁺-K⁺ ATPase pump.

How to Approach the Question

First, identify the molecule in the question: Insulin is a peptide hormone.
Recall the major classes of hormone action: 1) Enzyme-linked receptors, 2) G-protein coupled receptors with second messengers, and 3) Intracellular receptors that regulate genes.
Associate specific hormone types with their mechanisms. Peptide hormones like insulin and growth factors typically use enzyme-linked receptors.
Evaluate the options based on this classification. 'Activation of intracellular enzymes' is the defining feature of the enzyme-linked receptor pathway used by insulin.
Eliminate other options by linking them to different hormone classes: 'Activation of genes' is for steroids/thyroid hormones, and 'Via secondary messenger' is for hormones like glucagon that use GPCRs.

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