Active Transport: The Role of Pump Proteins
- Cells often need to absorb or expel substances against their concentration gradients, moving particles from a lower to a higher concentration.
- This process, called active transport, is carried out by specialized pump proteins embedded in the cell membrane.
Definition
Active transport
Active transport is the movement of molecules or ions across a membrane against their concentration gradient (from low to high concentration), which requires energy.
Unlike facilitated diffusion, which is passive, active transport requires energy in the form of ATP.
How Do Pump Proteins Work?
- Pump proteins are highly specialized and differ from channel proteins in three key ways:
- Energy Usage
- Pump proteins require energy to function and drive active transport, whereas diffusion through channel proteins is passive and does not use energy.
- Directionality
- Pump proteins transport particles across the membrane in only one direction.
- By contrast, channel proteins allow particles to move in either direction depending on the concentration gradient.
- Against the Gradient
- Pump proteins typically move particles against their concentration gradient (from low to high concentration).
- Facilitated diffusion, in contrast, always occurs down the concentration gradient.
- Energy Usage
Active transport is essential for maintaining concentration gradients that are critical for cellular functions, such as nutrient uptake and waste removal.
Mechanism of Pump Protein Action
- Pump proteins operate by switching between two conformations, powered by ATP:
- Particle Binding:
- In one conformation, the pump protein’s binding site faces the cytoplasm or extracellular space.
- This allows the target particle (ion or molecule) to bind.
- Particle Binding:
