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, for 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 Ca²⁺ from the endoplasmic reticulum to the cytosol works without ATP because it moves down the concentration gradient. The protein moving Ca²⁺ from the cytosol to the endoplasmic reticulum requires ATP because it moves against the concentration gradient.

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

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