Question

When the protein gramicidin is integrated into a membrane, an H channel forms and the membrane becomes very permeable to protons (H ions). If gramicidin is added to a lipid bilayer, what effect will it have on the membrane's permeability to H ions?

1) The membrane's permeability to H ions will decrease
2) The membrane's permeability to H ions will remain the same
3) The membrane's permeability to H ions will increase
4) The effect on the membrane's permeability to H ions cannot be determined

Answer 1

The addition of gramicidin to a lipid bilayer increases the membrane's permeability to hydrogen ions, as it forms a channel that facilitates their transport across the membrane.

Step-by-step explanation:

When gramicidin is added to a lipid bilayer, its role as an ion channel specifically facilitates the transport of hydrogen ions (protons) across the membrane. Gramicidin forms a channel that increases the membrane's permeability to H ions because it provides a path that allows these ions to bypass the hydrophobic core of the phospholipid bilayer, which they cannot normally cross unassisted.

Ion channels like gramicidin are crucial because they permit the flow of ions following an electrochemical gradient, without which charged particles could not easily pass through the nonpolar regions of the membrane. Hence, when gramicidin is integrated into a lipid bilayer, the permeability of the membrane to H ions will increase, which is essential for processes such as ATP synthesis in mitochondria.