Lecture 9: Transport Across Membranes

Selective permeability

membrane allows some substances through more easily than others.

Diffusion

spontaneous movement of molecules/ions.

Concentration gradient

difference in concentration across space.

Equilibrium

no net movement because movement occurs equally in both directions.

Electrochemical gradient

combination of concentration and electrical gradients.

Osmosis

diffusion of water across a selectively permeable membrane.

Passive transport

transport that does not require an outside energy source

Facilitated diffusion

passive transport using membrane proteins.

Channel protein

membrane protein that forms a passageway through the membrane.

Carrier protein

protein that changes shape to transport a molecule.

Aquaporin

channel protein that transports water.

Active transport

transport requiring energy to move substances against an electrochemical gradient.

Pump

membrane protein involved in active transport.

Primary active transport

uses ATP directly.

Secondary active transport

uses an electrochemical gradient created by another pump.

Symporter

moves substances in the same direction.

Antiporter

moves substances in opposite directions.