Question

Calcium ions (CA2+) are stored in the smooth ER. Some signaling pathways in the cell cause the ER to release the calcium ions into the cytoplasm, which causes the calcium ion concentration in the cytoplasm to increase and at the same time the calcium ions concentration in the ER to decrease. Once the signaling pathways is turned off, the calcium is returned to the ER so that the concentration of calcium in the ER is very high and the concentration in cytoplasm is almost zero. What membrane transport mechanism would you propose is used to return the calcium ions to the ER and why?

Your answer must include: what type of membrane protein would be used, the location of the membrane protein, and the description of how the membrane protein works.

Answer 1

Calcium ATPase/ SERCA pump would be used to transport calcium ions back from the cytosol to the ER. The location of the pump would be the membrane of the endoplasmic reticulum.

Mechanism of action- two molecules of calcium ions from the cytosol and one molecule of ATP binds to the transporter. One phosphate group from ATP is transported to an aspartate residue of the transporter. This phosphorylation causes the conformation change that decreases the affinity of transporter for bound calcium ions. calcium ions are released in the lumen of ER. Dephosphorylation of aspartte occurs to regenrate the original conformation that faces the calcium binding sites in the cytosol and has higjh affinity for calcium ions