How Glucose transport into the cell?

 How Glucose transport into the cell?

Glucose cannot diffuse directly into cells, but enters by  one of two transport mechanisms:

1.   Na⁺-independent, facilitated diffusion transport sys tem

2.   Na⁺-monosaccharide cotransporter system.

 

Na⁺-independent, facilitated diffusion transport sys tem

 

This system is mediated by a family of 14 glucose  transporters in cell membranes.They are designated GLUT-1 to GLUT-14 (glucose  transporter isoforms 1–14).

These transporters exist in the membrane in two  conformational states. Extracellular glucose binds to the transporter, which  then alters its conformation, transporting glucose across  the cell membrane. In facilitated diffusion, glucose movement follows a  concentration gradient, that is, from a high glucose concentration  to a lower one.

For example, GLUT-1, GLUT-3, and GLUT-4 are primarily  involved in glucose uptake from the blood.

 

Na⁺-monosaccharide cotransporter system.

This is an energy-requiring process that transports glucose  “against” a concentration gradient—that is, from low  glucose concentrations outside the cell to higher  concentrations within the cell.

This system is a carrier-mediated process in which the  movement of glucose is coupled to the concentration  gradient of Na⁺, which is transported into the cell at the  same time.

The carrier is a sodium-dependent–glucose transporter or  SGLT.

This type of transport occurs in the epithelial cells of the  intestine and renal tubules