Carrier proteins are specialized proteins found in cell membranes that help transport substances across the membrane. They bind to specific molecules, such as glucose or amino acids, and change shape to move these molecules into or out of the cell. This process is essential for maintaining the cell's internal environment and ensuring it has the necessary nutrients. These proteins work in various ways, including facilitated diffusion and active transport. In facilitated diffusion, carrier proteins help move substances along their concentration gradient without using energy. In contrast, active transport requires energy, often from ATP, to move substances against their concentration gradient, ensuring that cells can uptake vital nutrients even when they are in low supply.