Calcium ions (Ca²⁺) are present in the endoplasmic reticulum at concentrations 1,000 times higher than in the cytosol (the gel-like part of the cell outside organelles). One protein on the endoplasmic reticulum membrane is devoted to allowing Ca²⁺ to move from the endoplasmic reticulum to the cytosol, and another protein moves Ca²⁺ from the cytosol to the endoplasmic reticulum. These processes are not trivial-Ca²⁺ released into the cytosol allows, for example, muscle contraction and communication between nerve cells. In this pair of Ca²⁺ transport proteins, you would predict that the protein moving Ca²⁺ from the endoplasmic reticulum to the cytosol ________ and the protein that moves Ca²⁺ from cytosol to the endoplasmic reticulum ________.

Question

Quizplus · Accepted Answer

The protein moving calcium from the high concentration in the endoplasmic reticulum to the lower concentration in the cytosol can do so passively (without ATP), while the protein moving calcium against its concentration gradient from the cytosol back into the endoplasmic reticulum requires energy, thus ATP.

Calcium Ions (Ca2+) Are Present in the Endoplasmic Reticulum at Concentrations

Calcium Ions (Ca²⁺) Are Present in the Endoplasmic Reticulum at Concentrations