Answer
Primary active transport is powered by the chemical energy released by the hydroylsis of ATP utilizing the catalytic action of ATPase In secondary active transport the energy comes from the conversion of the potential energy of the high Na+ gradient in the extracellular fluid. When leaks develop in the plasma membrane, the potential energy of the high sodium concentration is transformed into kinetic energy as the sodium ions move (leak) into the cytosol. Leaking Na+ ions bind to a carrier proteins which also bind to other substances ; this changes the shape of the substance and that of the carrier protein and both Na+ion and changed substance are carried into the cell together. This is an example of secondary active transport by a symporter transport protein--both substances are carried in the same direction at the same time. Digested amino acids and glucose in the digestive tract are also carried into cells by Na-amino acids and Na-glucose symporters respectively .
Work Step by Step
Active secondary transport also utilizes the mechasnism of antiporters. In this case chemical moities are moved in a direction opposite to the movement of the N+ ions. Thus H+ ions and Ca++ ions are expelled from cells by secondary active transport through the agency of antiporter proteins.
