Final answer:
The protein involved in transporting molecules against their concentration gradient in the cell membrane likely binds to ATP, as it provides the necessary energy for active transport.
Step-by-step explanation:
A protein that transports molecules against their concentration gradient in the cell membrane typically requires energy to perform this action. The energy frequently comes in the form of ATP (adenosine triphosphate), which is the primary energy currency within cells. These proteins, often referred to as pumps, function by utilizing ATP to move substances such as ions or molecules from areas of low concentration to high concentration, which is a process known as active transport. The Sodium-Potassium Pump is a prominent example of this type of transport protein that actively exchanges sodium ions (Na+) for potassium ions (K+) across the plasma membrane.