TRANSPORTERS,
PUMPS, & CHANNELS

LEARNING OBJECTIVES

• Describe how solutes cross cell membranes
• Explain how charge, size, and solubility affect

solute movement across cell membranes.

• Contrast how transporters, pumps &
channels work
• Describe how ion channels are gated.

GENERAL CONCEPTS

1. Movement of a solute across the lipid bilayer (cell membrane)
is dependent on its size, charge, and solubility.
2. Net flux (movement) of a solute is determined by gradients.
3. A permeable solute crosses the membrane by simple
diffusion (slow), moving down its concentration gradient.
4. A non-permeable solute crosses the membrane by
facilitated diffusion (fast) using transporters. This process
requires a gradient, is saturable, and is specific.
5. Primary active transport moves a solute against its
concentration gradient. This mechanism requires energy (ATP),
exhibits specificity, and is saturable.
6. Secondary active transport couples the activity of a co-transporter
with a pump. This is used for transcellular transport of a solute.