Expert: Florence M Rollwagen - 4/22/2008

Question
For the facilitated transport of glucose, is an enzyme required?

Answer
For the facilitated transport of glucose, is an enzyme required?

Hello and thanks for your question.

The plasma membrane is impervious to most molecules, so special channels are required to allow materials to pass in and out of the cell.  There are three ways a cell obtains essential materials from the outside:  Diffusion, facilitated transport and active transport all move molecules across the plasma membrane.  Diffusion and facilitated transport do not require energy input, and move material along a concentration gradient, from high concentration to low concentration.  Active transport requires energy and moves material against the concentration gradient, from an area of low concentration to an area of high concentration.

Facilitated transport requires a special receptor that captures its target molecule (glucose) and allows it to pass through a special channel in the plasma membrane.  Transport is always from an area of high concentration to an area of low concentration and does not require energy input (ATP) from the cell.  So if glucose is in high concentration outside the cell the facilitated transport will move it into the cell at a faster rate than diffusion alone.  

Enzymes are usually required to break down or build up molecules.  So if glucose is broken down (as in glycolysis) enzymes are required for those steps.  Similarly, if glucose is built up into long chain polymers (starch), enzymes are required for those processes as well.

I hope this answers your question.  Please write back if you need more information.

FM Rollwagen, PhD