Q.6 Insulin-dependent glucose uptake by adipose tissue is the result of
1. cotransport of glucose with sodium against concentration gradient
2. simple diffusion of glucose down the concentration gradient
3. ATP-dependent transport of glucose against concentration gradient
4. transfer of GLUT transporters from intracellular vesicles to cell membrane
Insulin triggers glucose uptake in adipose tissue by relocating GLUT4 transporters to the cell membrane, a key process for post-meal glucose clearance. The correct answer is 4. transfer of GLUT transporters from intracellular vesicles to cell membrane.
Correct Answer
4. Transfer of GLUT transporters from intracellular vesicles to cell membrane
Insulin signaling causes GLUT4-containing vesicles to fuse with the plasma membrane, boosting facilitated diffusion of glucose into adipocytes. This rapid, reversible process accounts for 2-10 fold uptake increase within minutes.
All Options Explained
| Option | Description | Why Correct/Incorrect |
|---|---|---|
| 1. Cotransport of glucose with sodium against concentration gradient | Na+/glucose symport (SGLT proteins) moves glucose uphill using Na+ gradient. | Incorrect: Occurs in intestine/kidney, not insulin-responsive adipose tissue. |
| 2. Simple diffusion of glucose down the concentration gradient | Passive movement through lipid bilayer without transporters. | Incorrect: Glucose is polar; requires transporters like GLUT4, not simple diffusion. |
| 3. ATP-dependent transport of glucose against concentration gradient | Active transport via pumps (e.g., Na+/K+ ATPase indirectly). | Incorrect: Adipose uses facilitated diffusion; no direct ATP pump for glucose here. |
| 4. Transfer of GLUT transporters from intracellular vesicles to cell membrane | Insulin-stimulated GLUT4 exocytosis to plasma membrane. | Correct: Matches exact mechanism in adipocytes for insulin action. |
Mechanism Insight
In fasting, GLUT4 stays intracellular; insulin via PI3K-Akt pathway promotes vesicle trafficking, enabling glucose entry for lipogenesis. Dysregulation links to diabetes.
