Which membrane protein forms a hydrophilic channel to pass specific molecules?

• A. Enzymes
• B. Channel proteins
• C. Peripheral proteins
• D. Carrier proteins

Answer: (B)

Membrane transport proteins that span the lipid bilayer can create a continuous, hydrophilic pore. This pore forms a channel that allows specific ions or polar molecules to pass through the hydrophobic core of the membrane, moving down their concentration or electrochemical gradient without the solute having to flip across the membrane themselves. These channel proteins are designed to be selective and can be gated, opening or closing in response to signals.

In contrast, carrier proteins do not form a pore. They bind the solute on one side and undergo a conformational change to shuttle it to the other side, which is a different mechanism from forming a through-and-through channel. Enzymes are catalytic proteins, not transporters, and peripheral proteins typically sit on the membrane surface rather than spanning it to create a channel. So the protein that forms a hydrophilic channel for passing specific molecules is the channel protein.