Chapter 7.4, Problem 2CC

Summary Introduction

To explain: The reason why the sodium-potassium pump is not considered a cotransporter.

Introduction:

The Sodium-potassium pump is an active transport system that requires energy expenditure from adenosine triphosphate (ATP) to maintain an ion concentration gradient across the plasma membrane. This pump works by transporting three Na+ ions out of the cell for every two K+ ions entering the cell. In contrast, channel proteins allow molecules to diffuse down their concentration gradient, without energy expenditure. A cotransporter is a protein that couples a substance against its concentration gradient when a substance diffuses down its concentration gradient.