Question

Ca²⁺-pumps in the plasma membrane and endoplasmic reticulum are important for _________.

a. Maintaining osmotic balance.
b. Preventing Ca²⁺ from altering the activity of molecules in the cytosol.
c. Providing enzymes in the ER with Ca²⁺ ions that are necessary for their catalytic activity.
d. Maintaining a negative membrane potential.

Answer 1

Calcium pumps in the plasma membrane and endoplasmic reticulum prevent excess Ca²⁺ in the cytosol, which could disrupt molecular activity. These pumps achieve this by actively transporting Ca²⁺ out of the cytosol using ATP, crucial for cell signaling and regulation.

Step-by-step explanation:

The correct answer is preventing Ca²⁺ from altering the activity of molecules in the cytosol. Ca²⁺-pumps in the plasma membrane and endoplasmic reticulum are crucial for maintaining the low concentration of calcium ions within cells, which is necessary to prevent interference with molecular activities in the cytosol. The pumps use ATP to actively transport Ca²⁺ out of the cytosol, either by moving it to the extracellular space or into storage within the endoplasmic reticulum.

Calcium ions serve as a second messenger in numerous signaling pathways, but a high concentration of Ca²⁺ in the cytosol can be harmful. Thus, the pumps help to regulate cytosolic Ca²⁺ levels. When a signaling event occurs, Ca²⁺ channels in the cellular membranes open, allowing a controlled increase of Ca²⁺ into the cytosol to activate cellular responses such as muscle contraction or hormone secretion.