Topic 6: Transport across biological membranes

passive diffusion

no energy - small, uncharged molecules diffuse across bilayer membrane down concentration gradient; occurs until molecules are randomly distributed on both sides of membrane

facilitated diffusion

no energy - specific integral membrane proteins transport solutes down concentration gradient, allowing polar and charged molecules to pass through membrane without contacting hydrophobic bilayer

active transport

requires energy - pumping of ions or other charged or polar molecules against gradient, must be coupled to an exergonic rxn

osmosis

form of passive diffusion involving water

aquaporin

integral membrane protein that facilitates the transport of water across the cell membrane

hypotonic

solution with lower solute concentration than another solution, causing water to enter cells

isotonic

solution with equal solute concentration as another solution, resulting in no net movement of water across cell membranes

hypertonic

solution with higher solute concentration than another solution, causing water to leave cells

ion channel

facilitated diffusion - integral membrane protein that forms a “pore” to transport ions down the concentration gradient, opens/closes in response to signals

carrier protein

facilitated diffusion - integral membrane protein that binds specific solute on one side of membrane to carry solute down concentration gradient

glucose uniport

protein that facilitates the passive transport of glucose across the cell membrane, allowing it to move down its concentration gradient without energy input

ATP hydrolysis (pump)

active transport - breaks ATP into phosphate group and uses that energy to transport ions or other charged molecules against the gradient

co-transporter

active transport - latches onto something already going down its concentration gradient, and uses that energy to transport another molecule against its gradient

sodium-potassium ATPase

pump that transports sodium out of and potassium into the cell

exocytosis

cell secreting biological molecules by the fusion of vesicles with the plasma membrane

endocytosis

cell takes in molecules and particulate matter by forming new vesicles from the plasma membrane; reverse of exocytosis

phagocytosis

process by which a cell engulfs solid particles or other cells (eating)

pinocytosis

process by which a cell takes up external fluid with dissolved solutes (drinking)

receptor-mediated endocytosis

type of pinocytosis that enables the cell to acquire bulk quantities of specific substances by using surface receptors to bind molecules