Active Transport

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Active Transport

Sometimes substances must move from regions of lower concentrations to a region of higher concentration-against the passive movement from higher to lower concentration. This movement of substances across the plasma membrane against a concentration gradient requires energy; therefore, it is called active transport. 
Active transport occurs with the aid of carrier proteins, commonly called pumps. Some pumps move one type of substance in only one direction, while others move two substances either across the membrane in the same direction or in opposite directions. Because of active transport, the cell maintains the proper balance of substances it needs. Active transport helps maintain homeostasis. 

Sodium-Potassium ATPase Pump

One common active transport pump is called the sodium-potassium ATPase pump. This pump is an example of a transport protein and is found in the plasma membrane of animal cells. The pump is an enzyme that catalyzes the breakdown of an energy-storing molecule. The sodium-potassium ATPase pump maintains the level of sodium ions (Na+) and potassium ions (K+) inside and outside the cell. It uses energy to transport 3 Na+ out of the cell while moving 2 K+ into the cell. The high level of sodium outside of the cell creates a concentration gradient. Thus, transporting 3 Na+ out of the cell and into a higher concentration requires energy in the form of ATP. 

The sodium-potassium ATPase pump binds 3 intracellular __________ to the active binding sites on the pump. 

__________ attaches to the pump while the __________ are still bound to their active site. 

The breakdown of __________ to __________ causes the protein to change shape. The 3 __________ are released outside the cell. 

2 extracellular __________ bind to their active site on the pump.

Binding of the __________ causes the attached phosphate to be released from the pump. 

The release of the phosphate causes the pump to change back to its original shape. The 2 __________ are released into the cell. 

The Sodium-Potassium ATPase pump is an example of active transport, which requires energy to move substances from a higher concentration to a lower concentration.

Transport of Large Particles

Some substances are too large to move through the plasma membrane by diffusion or transport proteins; these substances must enter the cell by a different process. 

Endocytosis is the process by which a cell surrounds a substance in the outside environment, enclosing the substance in a portion of the plasma membrane. 

Exocytosis is the secretion of materials at the plasma membrane. Exocytosis is the reverse of endocytosis. Cells use exocytosis to expel wastes and to secrete substances, such as hormones, produced by the cell. 
Both endocytosis & exocytosis require the input of energy. 

Vacuoles are used
Cell surrounds a substance and brings it inside
Process maintains homeostasis
Too large to move through plasma membrane
Vesicles are used
Requires active transport
Cell expels wastes at the plasma membrane

Endocytosis
Exocytosis
Both