Membrane Transport (bio test 3)

passive transport

no energy required

active transport

energy required

what falls under passive transport?

• simple diffusion

• osmosis

• facilitated diffusion

what falls under active transport?

• molecular active transport

  • primary active transport

• bulk transport

  • exocytosis

  • endocytosis

    • receptor-mediated endocytosis

    • phagocytosis

    • pinocytosis

concentration gradient

• direction of flow (of molecules) in passive transport (high → low)

• molecules naturally travel down their gradient — from an area of higher concentration to an area of lower concentration — until they reach equilibrium, requiring no energy expenditure from the cell

simple diffusion

• Small molecules move directly through the lipid bilayer; no transport protein required

• examples: oxygen, carbon dioxide, nitrogen, water, dye (mostly small nonpolar substances)

• NO CHARGES!

• no energy required

osmosis

• Diffusion of water specifically (low solute/high) water → high solute/low water concentration

• no energy required

facilitated diffusion

• Uses channel/carrier proteins to move substances down gradient

• examples:

  • glucose: too big, needs channel to move

  • charged substances

  • water: uses aquaporins so it can move efficiently as a small polar substance

  • amino acids

  • ions

• no energy required

molecular active transport

• Uses transport proteins and ATP to move substances against their concentration gradient

• energy required

primary active transport

• Direct ATP use; protein pumps

• energy required

bulk transport

• Uses vesicles to move large amounts/or a large item in/out of the cell

• energy required

exocytosis

• Vesicles fuse with the membrane to export materials

• also used to build plasma membrane and cell wall

• energy required

endocytosis

• Membrane engulfs materials to form vesicles that bring them into the cell

• energy required

receptor-mediated endocytosis

• Specific uptake using receptors and coated vesicles

• cholesterol

• energy required

phagocytosis

• ‘Cell eating’ — engulfs large solid particles (bacterium)

• add digestive enzymes to the vesicle to destroy

• energy required

pinocytosis

• ‘Cell drinking’ — engulfs extracellular fluid; dissolves substances

• energy required