ACTIVE TRANSPORT Energy Used to Move Cellular Materials

Active transport always require ATP energy molecules

In order for ATP energy to be used by the cell, a high energy bond in the ATP molecule is broken, energy and a phosphate group is released. ADP is formed ATP ADP + P (& energy)

EXAMPLES OF ACTIVE TRANSPORT Cell Membrane Pumps (such as the Sodium-Potassium pump) Endocytosis & Exocytosis (such as pinocytosis and phagocytosis) Contractile vacuoles (such as the organelles in some protozoans)

Cell Membrane Pumps: Carrier proteins not only assist in passive transport, as in facilitated diffusion, but they can be used for active transport as cell membrane “pumps.”

During an active transport process, such as a cell membrane pump… The molecules transported by the carrier proteins are moved against the concentration gradient.

How does it work? A carrier protein binds to a specific molecule on one side of the membrane, changes shape (shielding the molecule from the phospholipids), transports the molecule to the other side, and then releases it.) 1) 2)

Example: Sodium-Potassium pump. Na+ K+ To function normally, many animal cells must have a higher concentration of Na+ ions outside the cell, & a higher concentration of K+ ions inside the cell. The complete cycle of the sodium-potassium pump transports 3 Na+ ions outside the cell, and 2 K+ ions inside the cell. (At top speed, it can transport 450 Na+ ions and 300 K+ ions per second!)

Sodium-Potassium Pump

Sodium-Potassium Pump is important for nerve cells. Carrying the 3 Na+ ions outside & 2 K+ inside produced an electrical gradient across the membrane. The outside of the membrane becomes positively charged, while the inside of the membrane becomes negative. The difference is important for the conduction of electrical impulses along nerve cells.

Endocytosis Endocytosis is a process by which cells ingest external fluid, macromolecules, and large particles including other cells.

During Endocytosis… The cell membrane forms a small pouch which pinches off in the cell to form a vesicle. Vesicles can fuse with lysosomes and their contents are digested with enzymes.

Two major types of endocytosis: pinocytosis – transport of solutes or fluids phagocytosis – movement of large particles or whole cells. unicellular organisms such as the amoebae can ingest bacteria and other protozoans, such as paramecia. Amoeba uses pseudopodia to engulf food.

phagocytes Some specialized white blood cells in animals, called phagocytes, can engulf bacteria & viruses. Lysosomes fuse with vesicles containing these invaders so they can be destroyed.

Exocytosis (the reverse of endocytosis) Vesicles fuse with the cell membrane, releasing their contents to the outside environment.

Cell may use exocytosis to release large molecules, such as proteins. (Vesicles from the Golgi apparatus fuse with the cell membrane to deliver their proteins to the outside of the cell.)

Unicellular organisms may get rid of wastes through exocytosis.

Also nerve cells (release neurotransmitters) and exocrine cells (release hormones to blood) release molecules to control the activities of other cells.

Contractile Vacuoles Many freshwater unicellular organisms must constantly rid themselves of excess water. The can do this by special structures called contractile vacuoles, which collect and pump water out of the cell.