Which membrane proteins form tunnels that allow import and export across the membrane?

Which membrane proteins form tunnels that allow import and export across the membrane?

• A. Channel proteins
• B. Peripheral proteins
• C. Integral proteins
• D. Glycoproteins

Answer: (A)

Channel proteins form hydrophilic tunnels through the lipid bilayer, creating a direct passage for ions and small molecules to cross the membrane. This pore allows substances to move quickly in or out, typically down their electrochemical gradient in facilitated diffusion, though some channels are gated to open or close in response to stimuli. Peripheral proteins sit on the membrane surface and don’t form pores, so they don’t create a tunnel for transport. Integral proteins cover a range of roles, but not all are pore-forming channels; many function as transporters that change shape to shuttle substances, rather than providing a continuous tunnel. Glycoproteins are mainly involved in cell recognition and adhesion, not transport.

Channel proteins form hydrophilic tunnels through the lipid bilayer, creating a direct passage for ions and small molecules to cross the membrane. This pore allows substances to move quickly in or out, typically down their electrochemical gradient in facilitated diffusion, though some channels are gated to open or close in response to stimuli. Peripheral proteins sit on the membrane surface and don’t form pores, so they don’t create a tunnel for transport. Integral proteins cover a range of roles, but not all are pore-forming channels; many function as transporters that change shape to shuttle substances, rather than providing a continuous tunnel. Glycoproteins are mainly involved in cell recognition and adhesion, not transport.