IB Biology Topic B2.1.7: Pump Proteins for Active Transport Notes

Active Transport: Pumps Move Substances Against the Gradient

1. Cells often need to move substances against their concentration gradient, from low to high concentration.
2. This process, called active transport, is done by pump proteins in the cell membrane.

Pumps Differ From Channels in Three Key Ways

1. Energy use
   1. Pumps need energy to work, while diffusion through channels is passive and uses none.
2. Direction
   1. Pumps move particles in only one direction.
   2. Channels let particles move either way, depending on the gradient.
3. Against the gradient
   1. Pumps move particles against their concentration gradient, from low to high.
   2. Facilitated diffusion always runs down the gradient.

Pumps Work by a Bind, Change Shape, Release Cycle

1. A pump protein switches between two shapes (conformations), powered by ATP.
2. Particle binding
   1. In the first shape, the binding site faces one side of the membrane.
   2. The target ion or molecule binds to that site.
3. Energy use and shape change
   1. ATP is hydrolyzed, releasing energy.
   2. This energy changes the pump's shape and shifts the particle across the protein.
4. Release
   1. The new shape exposes the particle to the other side, where it is released.
5. Resetting
   1. The pump returns to its original shape, ready to start again.

Example

• The sodium-potassium pump (Na⁺/K⁺ pump) pumps sodium ions out of the cell and potassium ions in.
• This keeps the ion gradients that cells rely on.

ATP Supplies the Energy for Pumping

1. Most pumps use ATP (adenosine triphosphate) as their energy source.
   1. ATP hydrolysis releases the energy the pump uses to change shape and move particles.
   2. Cellular respiration keeps making ATP so active transport has a steady supply.

Active Transport Keeps Cells Alive and Working

1. Active transport lets cells hold the concentration gradients that life depends on.
2. Without it, cells could not do several essential jobs.
   1. Absorb vital nutrients against a concentration gradient.
   2. Remove toxic waste products.
   3. Sustain processes like nerve signaling and muscle contraction.