Principles of Biology (POB) Exam 2 Practice

The main idea is how different membrane proteins move substances across the membrane. The sodium-potassium pump is a transporter that uses energy from ATP to change shape and move ions against their gradients—three Na+ out and two K+ in. This fits the definition of a carrier protein, a transporter that cycles between conformations to shuttle solutes across the membrane. It isn’t a channel, which would form a hollow pore permitting ions to flow passively down their gradients, and while the pump has ATPase activity (an enzymatic function), its role in actively moving ions across the membrane is defined by being a transporter.