Glucose, a vital source of energy for cells, cannot passively diffuse through the plasma membrane due to its polar nature. The plasma membrane comprises a phospholipid bilayer that is hydrophobic and serves as a barrier to most polar molecules, including glucose.
To enter the cell, glucose relies on a specific transport mechanism known as facilitated diffusion. This process involves the use of transport proteins, such as glucose transporter proteins (GLUT), embedded in the membrane. These proteins provide a pathway for glucose to move down its concentration gradient, from an area of higher concentration outside the cell to lower concentration inside, without the expenditure of energy.
For instance, GLUT1 is a well-known glucose transporter that facilitates the uptake of glucose in various tissues. When glucose binds to GLUT1, a conformational change occurs in the protein, allowing glucose to be released inside the cell. This efficient mechanism ensures cells receive the glucose they need for metabolism while respecting the selective permeability of the plasma membrane.