Final answer:
Active transport involves transport proteins known as pumps, which use energy from ATP to move substances across cell membranes against their concentration gradient, altering the protein's shape during the process.
Step-by-step explanation:
When active transport utilizes transport proteins to move substances across a membrane against the concentration gradient, ATP (energy) is required. These transport proteins, often referred to as pumps, undergo a change in shape to transport the substance across the cell membrane. An example is the sodium-potassium pump, where ATP transfers a phosphate group to the pump, triggering a change in its shape and allowing it to move ions against their concentration gradient. This is essential for functions such as neurons transmitting signals to the brain, where protein pumps actively transport molecules.
The process of active transport is crucial for maintaining correct concentrations of ions and other substances inside the cell. Active transport proteins can be uniporters, symporters, or antiporters, each facilitating the movement of specific ions or molecules across the cell membrane. Once the transport is complete and the ATP is hydrolyzed, the protein pump reverts to its original state, ready to perform another cycle of transport.