* Sugar molecules are polar: This means they are hydrophilic (water-loving) and cannot easily pass through the hydrophobic (water-fearing) lipid bilayer of the cell membrane.
* Facilitated diffusion: This process utilizes transport proteins embedded within the cell membrane. These proteins have specific binding sites for sugar molecules, allowing them to move across the membrane down their concentration gradient (from an area of high concentration to an area of low concentration). This process is passive, meaning it doesn't require energy.
Here's how facilitated diffusion works with sugar:
1. Binding: A sugar molecule binds to a specific transport protein on the membrane.
2. Conformational change: The binding of the sugar molecule causes a change in the shape of the protein, opening a passageway through the membrane.
3. Movement: The sugar molecule passes through the protein channel and into the cell.
4. Release: Once the sugar is inside the cell, it detaches from the protein, allowing the protein to bind to another sugar molecule.
Note: While facilitated diffusion is the primary mechanism for sugar transport, some cells may use active transport to move sugar against its concentration gradient. This requires energy and is usually coupled with other processes like the sodium-potassium pump.
