Which statement describes the carrier protein mechanism of transport, moving a specific molecule across the membrane by binding and releasing it?

Which statement describes the carrier protein mechanism of transport, moving a specific molecule across the membrane by binding and releasing it?

• A. Receptor Protein
• B. Enzymatic Proteins
• C. Channel Protein
• D. Carrier Protein

Answer: (D)

Carrier proteins move specific molecules across membranes by binding the molecule on one side, changing shape to shuttle it through, and releasing it on the other side. This binding-and-release with a conformational change makes the transport selective and saturable, since only a finite number of carrier proteins are available to carry the cargo. This mechanism is different from channel proteins, which form a pore that provides a direct path for diffusion without a shape change, and from receptor proteins or enzymes, which bind or act on substrates but do not transport the molecule across the membrane. Carrier-mediated transport can occur passively down a gradient (facilitated diffusion) or be energy-dependent (active transport) if moving against the gradient.

Carrier proteins move specific molecules across membranes by binding the molecule on one side, changing shape to shuttle it through, and releasing it on the other side. This binding-and-release with a conformational change makes the transport selective and saturable, since only a finite number of carrier proteins are available to carry the cargo. This mechanism is different from channel proteins, which form a pore that provides a direct path for diffusion without a shape change, and from receptor proteins or enzymes, which bind or act on substrates but do not transport the molecule across the membrane. Carrier-mediated transport can occur passively down a gradient (facilitated diffusion) or be energy-dependent (active transport) if moving against the gradient.