Active Transport

  • In certain instances, molecules are transported from an area of low concentration to an area of high concentration.
  • Examples of this type of transport include the epithelial linig of the small intestines that transport glucose from the lumen into the cells and the transport of calcium from the intracellular compartment to the extracellular compartment so that the extracellular concentration of calcium is from 1000 to 10,000 times the intracellular concentration.
  • This transport requires carrier molecules and energy.
  • Energy is obtained from the enzymatic hydrolysis of one phosphate bond from an adenosine triphosphate molecule (ATP).
  • In a similar fashion to facilitated diffusion, active transport shows the characteristics of Specificity, Competition and Saturation.
  • The difference is the fact that active transport is completely inhibited if the enzyme system is poisoned e.g. cyanide while facilitated diffusion is not affected by metabolic poisons.