ion gradients, ion transporters, ion channels

ion gradients

Concentration difference in ion concentration across membrane, resulting in membrane potential ranging from -40mV to -80mV

Energy source in transport processes

excitable membranes

essential for neuronal activity (action potential)

ion gradients across membranes

Plasma membrane: low Na+, high K+ inside cell

Intracellular organelles (vacuoles, lysosomes, endosomes, etc): proton gradient

Ca2+ gradients

sodium pump

Maintains sodium/potassium gradient across the plasma membrane

Inside: 10mM Na+, 100mM K+

Outside: 140mM Na+, 10mM K+

Per ATP molecule hydrolysed…

3 Na+ out 2 K+ in

ion channels

Facilitate ion flow across the membrane - form an aqueous pore across the membrane

Ions passing through a channel down the ion gradient - form higher to lower concentration

structural feature of ion membranes

amphipathic helices (hydrophobic side towards lipid environment, hydrophilic side towards pore)

Form aqueous pore

Transmembrane helices tightly packed

ion channels are gated

they open only in response to a cellular event