Question

The bacterial Na⁺- H⁺ antiporter is a secondary active transport protein that excretes excess Na⁺ from the cell. Is the extracellular pH higher or lower than the intracellular pH?

Short answer

Excess Na⁺ is excreted out when the pH of the bacterial extracellular environment is high.

Step-by-step solution

Introduction

Secondary active transport is the movement of molecules across the cell membraneusing an electrochemical gradient created by the pumping of ions out of the cell. The co-transport of Na⁺ is enabled by the creation of aconcentration gradient.

Extracellular pH is higher or lower than intracellular pH

The bacterial Na⁺- H⁺ antiporter is a secondary active transport proteinthat transports the cell's surplus Nat ion. When a protein works as an antiporter, it continues to go down the electrochemical gradientinto the cell. This process generates free energy in the cell, which is used to drive N⁺ export.

The bacterium Escherichia colipossesses two Na⁺/H⁺ antiporter genes, nhaA, and nhaB. In this case, the nhaA gene is necessary for high salinity and basic pH growth in the presence of Na⁺.

The nhaB gene improves toleranceto low Na⁺ concentrations. As a result, the nhaA gene is sensitive to high pH. Excess Na⁺ is excreted if the pH of the bacterial extracellular environment is high.