Summary of Active Transport
The combined gradient that affects an ion includes its concentration gradient and its electrical gradient. A positive ion, for example, might tend to diffuse into a new area, down its concentration gradient, but if it is diffusing into an area of net positive charge, its diffusion will be hampered by its electrical gradient. When dealing with ions in aqueous solutions, a combination of the electrochemical and concentration gradients, rather than just the concentration gradient alone, must be considered.
Living cells need certain substances that exist inside the cell in concentrations greater than they exist in the extracellular space. Moving substances up their electrochemical gradients requires energy from the cell. Active transport uses energy stored in ATP to fuel this transport.
Active transport of small molecular-sized materials uses integral proteins in the cell membrane to move the materials. These proteins are analogous to pumps. Some pumps, which carry out primary active transport, couple directly with ATP to drive their action. In co-transport (or secondary active transport), energy from primary transport can be used to move another substance into the cell and up its concentration gradient.
Glossary of Words
method of transporting material that requires energy
transporter that carries two ions or small molecules in different directions
gradient produced by the combined forces of an electrical gradient and a chemical gradient
pump that creates a charge imbalance
Primary active transport
active transport that moves ions or small molecules across a membrane and may create a difference in charge across that membrane
active transport mechanism that works against electrochemical gradients
Secondary active transport
movement of material that is due to the electrochemical gradient established by primary active transport
transporter that carries two different ions or small molecules, both in the same direction
specific carrier proteins or pumps that facilitate movement
transporter that carries one specific ion or molecule