Membrane transport proteins can function as channels or carriers.

Membrane transport proteins can function as channels or carriers.

• A. Enzymes that synthesize lipids
• B. Receptors only
• C. Carriers that change shape to move substances
• D. Structural anchors only

Answer: (C)

Membrane transport proteins come in two main forms: channels and carriers. The statement that best fits is about carriers that change shape to move substances. Carrier proteins bind specific molecules on one side of the membrane and then undergo a conformational change, which reorients the binding site to release the molecule on the other side. This mechanism lets the protein shuttle substances across the bilayer, either down or up a gradient depending on energy input. Channels, by contrast, form pores that allow ions or water to pass through the membrane when open, typically down their electrochemical gradient, without a substantial shape change tied to transporting each molecule. The other options describe proteins that don’t transport substances across membranes: lipid-synthesizing enzymes are metabolic catalysts, receptors mainly bind and relay signals rather than move substances, and structural anchors provide attachment points rather than translocation.

Membrane transport proteins come in two main forms: channels and carriers. The statement that best fits is about carriers that change shape to move substances. Carrier proteins bind specific molecules on one side of the membrane and then undergo a conformational change, which reorients the binding site to release the molecule on the other side. This mechanism lets the protein shuttle substances across the bilayer, either down or up a gradient depending on energy input.

Channels, by contrast, form pores that allow ions or water to pass through the membrane when open, typically down their electrochemical gradient, without a substantial shape change tied to transporting each molecule. The other options describe proteins that don’t transport substances across membranes: lipid-synthesizing enzymes are metabolic catalysts, receptors mainly bind and relay signals rather than move substances, and structural anchors provide attachment points rather than translocation.