Question

In most cells, there are electrochemical gradients of many ions across the plasma membrane even though there are usually only one or two electrogenic pumps present in the membrane. The gradients of the other ions are most likely accounted for by

A) cotransport proteins.
B) ion channels.
C) carrier proteins.
D) passive diffusion across the plasma membrane.
E) cellular metabolic reactions that create or destroy ions.

Answer 1

Ion gradients other than those directly moved by pumps are typically maintained through cotransport proteins, which utilize the energy from the electrogenic pumps' activity to transport other ions or molecules against their gradients, a process that plays a critical role in cellular function.

Step-by-step explanation:

The gradients of ions across the plasma membrane in cells are primarily maintained by active transport mechanisms which involve the expenditure of energy, typically in the form of ATP. These gradients are essential for various physiological processes, such as nerve impulse transmission and muscle contractions. While only a few electrogenic pumps like the sodium-potassium pump directly use ATP to create these gradients, other ion gradients are managed indirectly through mechanisms such as cotransport proteins, which include symporters and antiporters, as well as ion channels that facilitate the passive movement of ions.

Cotransport proteins are responsible for:

1. The gradients of ions other than those directly moved by pumps are likely maintained by cotransport proteins.
2. Cotransport involves the active transport of one substance coupled with the passive transport of another.

Cells expend a significant portion of their metabolic energy to maintain ion concentrations across plasma membranes, crucial for their survival and function. Active transport proteins, such as uniporters, symporters, and antiporters, are integral in these processes. For instance, the symporter might use the downhill movement of one ion that was actively pumped out of the cell to drive the uphill transport of another ion or molecule into the cell. This is known as secondary active transport or co-transport. These transport mechanisms are essential for accumulating substances the cells require in higher concentrations than those outside the cellular environment. They also maintain the electrochemical gradients necessary for various cellular functions. All of this underscores the intricacy of membrane transport and the vital role of proteins in navigating the delicate balance of intracellular and extracellular ion concentrations.