ACTIVE TRANSPORTCell Membrane PumpsEndocytosisExocytosis
ACTIVETRANSPORT In many cases, cells must move molecules UP against their concentration gradient. Moving materials from areas of LOW concentration to areas of HIGH concentration requires ENERGY. Cells must expend energy (ATP) to transport the materials UP their concentration gradient.
CELL MEMBRANE PUMPS Carrier proteins not only assist in passive transport (helping move specific molecules DOWN their concentration gradients through facilitated diffusion)but also help with some types of active transport. Carrier proteins that serve in active transport are called cell membrane pumps because they move substances UP their concentration gradients.
HOW CELL MEMBRANE PUMPS WORK 1. Carrier Protein (pump) binds to a specific kind of molecules on one side of the cell membrane (where the concentration is LOW). 2. Protein (pump) changes shape, shielding molecules for the hydrophobic interior of the lipid bilayer. 3. Protein (pump) then transports (moves) the molecule across the membrane and releases it on the other side (where the concentration is HIGH). 4. Energy (ATP) is required to operate the pump.
ACTIVE TRANSPORT Macromolecules and food particles are too large to pass through the cell membrane by the transport processes we have studied so far. Any ideas on how to get those into the cell? How did you get the candy into your bag without breaking any of the rules?
ENDOCYTOSIS (IT TAKES ENERGY!!!!) Process by which cells ingest external fluid, macromolecules, and large particles (including other cells!). The external materials are enclosed by a portion of the cell, which folds into itself and forms a pouch. The pouch pinches off from the cell membrane and becomes a membrane-bound organelle called a vesicle that will later fuse with lysosomes or other membrane-bound organelles.
TWO TYPES OF ENDOCYTOSIS Biologists distinguish two types of endocytosis, based on the kind of material that is taken into the cell. Pinocytosis involves the transport of solutes or fluids. (cell drinking) Phagocytosis is the ingestion of large particles or whole cells. (cell eating) How would this be useful? Unicellular organisms feed by phagocytosis. Certain animal cells use phagocytosis to ingest bacteria and viruses that invade the cell (we call cells that do this phagocytes). Lysosome fuse with the vesicle formed to destroy the bacteria or virus before it can harm the animal.
EXOCYTOSIS (IT TAKES ENERGY!!!!) Exocytosis is endocytosis in reverse. Vesicles in the cytoplasm fuse with the cell membrane then release their contents into the cell’s external environment. Cells may use exocytosis to release large molecules like proteins. Which organelle would have made the protein? Which organelle would have packaged it in a vesicle to get it ready to ship?