Active Transport Review

ATP (adenosine triphosphate): compound used as a source of chemical energy in cells

· Living organisms require a continuous supply of energy to power energy requiring processes of life including reproduction, protein synthesis and certain forms of transport across cell membranes. The breakdown of ATP is what provides this energy.

Structure of ATP

Active transport: the movement of substances through the molecule against a concentration gradient using membrane-bound carrier protein and energy from ATP. The membrane requiring transport attaches to the open binding site on one side of the carrier protein. On the other side of the protein ATP is converted to ADP and releases energy. This causes a change in shape of the carrier protein and the solute is carried to the other side of the membrane.

There are varying active transport pumps found in the membranes of different cells which require ATP for energy. Nerve and muscle cells function properly through the movement of potassium and sodium through the sodium-potassium pump.

Bulk transportation: the movement of large quanities of materials into and or out of a cell. Simillar to active transport bulk transport requires the utilization of ATP for energy. Endocytosis and Exocytosis are the two forms of bulk transport.

Endocytosis: brings large quantity of material into the cell from the extracellular fluid. Phagocytosis and Pinocytosis are the two forms of endocytosis.

a) Phagocytosis (“cell eating”): the bulk transport of solids into the cell

E.g. macrophages- white blood cells that remove harmful invading bacteria by phagocytosis

b) Pinocytosis (“cell drinking”): the bulk transport of liquids into the cell

Exocytosis: the movement of larger materials out of the cell by means of secretory vesicles (membrane sacs). In some cases proteins produced by the ER are packaged into secretory vesicles by the Golgi apparatus and transported via exocytosis.