Chapter 13: Membrane Channels and Pumps

Exam 3

simple diffusion

The movement of molecules down a concentration gradien (high to low concentrations)

facilitated diffusion/passive transport

protein in membrane forms pore/channel to allow polar molecules to pass through membrane

• moves down a concentration gradien (high to low concentrations)

• has specificity to channels

• often gated (voltage or ligand-gated)

active transport

transport of ion/molecule against a concentration gradient (low to high concentrations)

• requires input of energy to transport molecule

electrochemical/membrane potential

energetic cost that is required to establish a concentration gradient of a charged species across a membrane

pumps

Membrane proteins that catalyze the active transport of ions against their electrochemical gradients

primary active transport

ATP hydrolysis is used as the energy input

P-type ATPase

A class of pumps whose reaction mechanism includes a phosphorylaspartate intermediate

carrier

A membrane protein that transports ions or molecules across the membrane without hydrolysis of ATP

secondary active transport

don’t use ATP directly as energy

• use moving one molecule/ion down its concentration gradient as the energy input to move molecule against concentration gradient

secondary transporter/cotransporter

A transporter that uses the energy of the downhill (exergonic) flow of one ion or molecule to power the uphill (endergonic) flow of another

anti porter

A secondary transporter that couples the downhill flow of one species to the uphill flow of another in the opposite direction across the membrane

symporter

A secondary transporter that couples the downhill flow of one species to the uphill flow of another in the same direction across the membrane

lactose permease

secondary active transporter in E. cli

• uses H+ gradient to facilitate uptake of lactose into the cell

uniporter

A secondary transporter that can transport a specific species in either direction governed only by concentrations of that species on either side of the membrane